Version Control with Subversion

Version Control with Subversion
Draft Revision 8942
Ben Collins-Sussman
Brian W. Fitzpatrick
C. Michael Pilato
Version Control with Subversion: Draft Revision 8942
by Ben Collins-Sussman, Brian W. Fitzpatrick, and C. Michael Pilato
Published (TBA)
Table of Contents
Preface .........................................................................................................................11
Audience ..............................................................................................................11
How to Read this Book ........................................................................................... 11
Conventions Used in This Book ................................................................................ 12
This Book is Free ................................................................................................... 12
Acknowledgments ..................................................................................................12
1. Introduction ...............................................................................................................1
What is Subversion? ...............................................................................................1
Subversion's History ...............................................................................................1
Subversion's Features ..............................................................................................2
Installing Subversion ..............................................................................................3
Subversion's Components ........................................................................................3
Client Components (for the User) ...................................................................... 3
Server Components (for the Administrator) ......................................................... 3
2. Basic Concepts ...........................................................................................................4
The Repository ......................................................................................................4
Versioning Models .................................................................................................5
The Problem of File-Sharing ............................................................................ 5
The Lock-Modify-Unlock Solution ....................................................................5
The Copy-Modify-Merge Solution ....................................................................7
Subversion in Action ..............................................................................................8
Working Copies .............................................................................................8
How Working Copies Track the Repository ........................................................ 14
The Limitations of Mixed Revisions .................................................................. 15
Summary ..............................................................................................................15
3. Guided Tour ..............................................................................................................16
Help! ...................................................................................................................16
Import ..................................................................................................................16
Revisions: Numbers, Keywords, and Dates, Oh My! ..................................................... 16
Revision Numbers ..........................................................................................16
Revision Keywords ........................................................................................17
Revision Dates ..............................................................................................17
Initial Checkout .....................................................................................................19
Basic Work Cycle ..................................................................................................20
Update Your Working Copy ............................................................................. 21
Make Changes to Your Working Copy ............................................................... 22
Examine Your Changes ...................................................................................23
Resolve Conflicts (Merging Others' Changes) ...................................................... 28
Commit Your Changes ....................................................................................31
Examining History .................................................................................................32
svn log .........................................................................................................33
svn diff ........................................................................................................34
svn cat .........................................................................................................36
svn list .........................................................................................................36
A Final Word on History ................................................................................. 37
Other Useful Commands .........................................................................................37
svn cleanup ...................................................................................................37
svn import ....................................................................................................37
Summary ..............................................................................................................38
4. Branching and Merging ............................................................................................... 39
What's a Branch? ...................................................................................................39
Using Branches .....................................................................................................40
Version Control with Subversion
Creating a Branch ..........................................................................................41
Working with Your Branch .............................................................................. 43
The Moral of the Story .................................................................................... 45
Copying Changes Between Branches ......................................................................... 46
Copying Specific Changes ...............................................................................46
Best Practices for Merging ............................................................................... 48
Common Use-Cases for Merging .............................................................................. 50
Merging a Whole Branch to Another .................................................................. 50
Undoing Changes ...........................................................................................51
Resurrecting Deleted Items ..............................................................................52
Switching a Working Copy ...................................................................................... 53
Tags ....................................................................................................................55
Creating a Simple Tag ..................................................................................... 55
Creating a Complex Tag .................................................................................. 56
Branch Maintenance ...............................................................................................56
Repository Layout ..........................................................................................56
Data Lifetimes ...............................................................................................57
Summary ..............................................................................................................58
5. Repository Administration ............................................................................................59
Repository Basics ...................................................................................................59
Understanding Transactions and Revisions .......................................................... 59
Unversioned Properties ...................................................................................59
Berkeley DB .................................................................................................60
Repository Creation and Configuration ....................................................................... 61
Hook Scripts .................................................................................................62
Berkeley DB Configuration ..............................................................................64
Repository Maintenance ..........................................................................................64
An Administrator's Toolkit ...............................................................................64
Repository Cleanup ........................................................................................73
Managing Disk Space .....................................................................................75
Repository Recovery ......................................................................................76
Migrating a Repository ....................................................................................77
Repository Backup .........................................................................................80
Adding Projects .....................................................................................................81
Choosing a Repository Layout .......................................................................... 81
Creating the Layout, and Importing Initial Data ................................................... 83
Summary ..............................................................................................................84
6. Server Configuration ...................................................................................................85
Network Model .....................................................................................................86
Requests and Responses ..................................................................................86
Client Credentials Caching ...............................................................................86
svnserve, a custom server ........................................................................................ 88
Invoking the Server ........................................................................................88
Built-in authentication and authorization ............................................................. 89
SSH authentication and authorization ................................................................. 91
httpd, the Apache HTTP server ................................................................................. 92
Prerequisites .................................................................................................93
Basic Apache Configuration .............................................................................94
Authentication Options ...................................................................................95
Authorization Options .....................................................................................98
Extra Goodies ................................................................................................103
Supporting Multiple Repository Access Methods ......................................................... 104
7. Advanced Topics ........................................................................................................106
Runtime Configuration Area ....................................................................................106
Configuration Area Layout ..............................................................................106
Configuration and the Windows Registry ............................................................ 107
Configuration Options .....................................................................................108
Version Control with Subversion
Properties .............................................................................................................112
Why Properties? ............................................................................................112
Manipulating Properties ..................................................................................113
Special properties ...........................................................................................116
Externals Definitions ..............................................................................................122
Vendor branches ....................................................................................................123
General Vendor Branch Management Procedure .................................................. 124
8. Developer Information .................................................................................................128
Layered Library Design ...........................................................................................128
Repository Layer ...........................................................................................129
Repository Access Layer .................................................................................134
Client Layer ..................................................................................................137
Using the APIs ......................................................................................................137
The Apache Portable Runtime Library ............................................................... 138
URL and Path Requirements ............................................................................ 138
Using Languages Other than C and C++ ............................................................. 138
Inside the Working Copy Administration Area ............................................................. 140
The Entries File .............................................................................................141
Pristine Copies and Property Files ..................................................................... 142
WebDAV .............................................................................................................142
Programming with Memory Pools ............................................................................. 143
Contributing to Subversion ......................................................................................145
Join the Community .......................................................................................145
Get the Source Code ....................................................................................... 146
Become Familiar with Community Policies ......................................................... 146
Make and Test Your Changes ........................................................................... 146
Donate Your Changes .....................................................................................147
9. Subversion Complete Reference .................................................................................... 148
The Subversion Command Line Client: svn ................................................................. 148
svn Switches .................................................................................................148
svn Subcommands ..........................................................................................151
svnadmin ..............................................................................................................208
svnadmin Switches .........................................................................................208
svnadmin Subcommands .................................................................................209
svnlook ................................................................................................................218
svnlook Switches ...........................................................................................218
svnlook Subcommands ....................................................................................219
A. Subversion for CVS Users ........................................................................................... 233
Revision Numbers Are Different Now ........................................................................ 233
Directory Versions .................................................................................................233
More Disconnected Operations .................................................................................234
Distinction Between Status and Update ...................................................................... 234
Branches and Tags .................................................................................................235
Meta-data Properties ...............................................................................................236
Conflict Resolution ................................................................................................236
Binary Files and Translation ..................................................................................... 236
Versioned Modules ................................................................................................237
Authentication .......................................................................................................237
Converting a Repository from CVS to Subversion ........................................................ 237
B. Troubleshooting .........................................................................................................238
Common Problems .................................................................................................238
Problems Using Subversion .............................................................................238
Problems Building Subversion ..........................................................................241
C. WebDAV and Autoversioning ...................................................................................... 242
Basic WebDAV Concepts ........................................................................................242
Just Plain WebDAV .......................................................................................242
DeltaV Extensions ..........................................................................................243
Version Control with Subversion
Subversion and DeltaV ............................................................................................244
Mapping Subversion to DeltaV ......................................................................... 244
Autoversioning Support ...................................................................................244
The mod_dav_lock Alternative .........................................................................245
Autoversioning Interoperability ................................................................................246
Win32 WebFolders ........................................................................................246
Mac OS X ....................................................................................................246
Unix: Nautilus 2 ............................................................................................247
Linux davfs2 .................................................................................................247
D. Other Subversion Clients ............................................................................................. 248
Out of One, Many .................................................................................................. 248
E. Third Party Tools ....................................................................................................... 249
Repository Converters .............................................................................................249
ViewCVS .............................................................................................................249
SubWiki ...............................................................................................................250
Glossary .......................................................................................................................251
List of Figures
2.1. A Typical Client/Server System .................................................................................. 4
2.2. The Problem to Avoid ............................................................................................... 5
2.3. The Lock-Modify-Unlock Solution .............................................................................. 6
2.4. The Copy-Modify-Merge Solution ............................................................................... 7
2.5. …Copy-Modify-Merge Continued ...............................................................................8
2.6. The Repository's Filesystem ....................................................................................... 9
2.7. The Repository ........................................................................................................12
4.1. Branches of Development .......................................................................................... 39
4.2. Starting Repository Layout ......................................................................................... 40
4.3. Repository With New Copy ........................................................................................ 42
4.4. The Branching of One File's History ............................................................................ 43
8.1. Subversion's "Big Picture" ......................................................................................... 129
8.2. Files and Directories in Two Dimensions ...................................................................... 131
8.3. Revisioning Time—the Third Dimension! ..................................................................... 132
List of Tables
2.1. Repository Access URLs ........................................................................................... 11
6.1. Network Server Comparison ....................................................................................... 85
8.1. A Brief Inventory of the Subversion Libraries ................................................................ 128
List of Examples
5.1. Using svnshell to Navigate the Repository .................................................................... 72
5.2. (Reporting Outstanding Transactions) ........................................................... 74
6.1. A sample configuration for anonymous access. .............................................................. 100
6.2. A sample configuration for authenticated access. ............................................................ 100
6.3. A sample configuration for mixed authenticated/anonymous access. .................................. 101
7.1. Sample Registration Entries (.reg) File. ........................................................................ 108
8.1. Using the Repository Layer ........................................................................................ 133
8.2. Using the Repository Layer with Python ....................................................................... 139
8.3. A Simple Script to Check Out a Working Copy. ............................................................. 140
8.4. Contents of a Typical .svn/entries File .......................................................................... 141
8.5. Effective Pool Usage ................................................................................................. 144
“If C gives you enough rope to hang yourself, think of Subversion as a sort of rope
storage facility.” —Brian Fitzpatrick
In the world of open-source software, the Concurrent Versions System (CVS) has long been the tool of
choice for version control. And rightly so. CVS itself is free software, and its wonderful “non-locking”
system—which allows dozens of far-flung programmers to share their work—fits the collaborative nature of the open-source world very well. CVS and its semi-chaotic development model have become
cornerstones of open-source culture.
But like many tools, CVS is starting to show its age. Subversion is a relatively new version control system designed to be the successor to CVS. The designers set out to win the hearts of CVS users in two
ways: by creating an open-source system with a design (and "look and feel") similar to CVS, and by attempting to fix most of CVS's noticeable flaws. While the result isn't necessarily the next great evolution
in version control design, Subversion is very powerful, very usable, and very flexible.
This book is written to document version 1.0 of the Subversion version control system. There are already a number of features and improvements planned for follow on versions of Subversion that may
change some of the commands and specific notes in this book.
This book is written for computer literate folk who want to use Subversion to manage their data. While
Subversion runs on a number of different operating systems, its primary user interface is command-line
based. For that reason, the examples in this book assume the reader is using a Unix-like operating system, and is relatively comfortable with Unix and command-line interfaces.
Not to fear, Microsoft Windows users can download a pre-compiled Windows native Subversion command-line client that works in the Command Prompt application. Many examples of the client will work
in the Command Prompt, but you may have more success if you run the examples inside the Cygwin
Unix emulation environment.
Most readers are probably programmers or sysadmins who need to track changes to source code; this is
the most common use for Subversion, and therefore it is the scenario underlying all of the book's examples. But keep in mind that Subversion can be used to manage changes to any sort of information: images, music, databases, documentation, and so on. To Subversion, all data is just data.
While this book is written with the assumption that the reader has never used version control, we've also
tried to make it easy for former CVS users to get up to speed quickly. Special sidebars may discuss CVS
from time to time, and a special appendix summarizes most of the differences between CVS and Subversion.
How to Read this Book
This book aims to be useful to people of widely different backgrounds: from people with no experience
in version control, all the way up to experienced sysadmins. Depending on your own background, certain chapters may be more or less important to you.
What kind of reader are you?
The experienced sysadmin or computer geek. The assumption here is that you've probably used CVS
before, and are dying to get a Subversion server up and running ASAP. Chapters 5 and 6 will show
you how to create your first repository and make it available over the network. After that's done,
chapter 3 and appendix A are the fastest routes to learning the Subversion client while drawing on
your CVS experience.
The new user. Your administrator has probably set up Subversion already, and you need to learn how
to use the client. If you've never used CVS (or have never used a version control system), then chapters 2 and 3 are a vital introduction. If you're already an old hand at CVS, chapter 3 and appendix A
are the best place to start.
The advanced user. Whether you're a user or administrator, eventually your project will grow larger.
You're going to want to learn how to do more advanced things with Subversion, such as branching
and merging (chapter 4), set metadata properties and configure runtime options (chapter 7), and
other things. Chapters 4 and 7 aren't vital at first, but be sure to read them once you're comfortable
with the basics.
The developer. Presumably, you're already familiar with Subversion, and now want to either extend
it, or build new software on top of its many APIs. Chapter 8 is just for you.
The book ends with reference material: chapter 9 is a reference guide for all Subversion commands, and
the appendices cover a number of useful topics. These are the chapters you're mostly likely to come
back to after you've finished the book.
Conventions Used in This Book
### O'Reilly almost certainly needs to fill this in, depending on how they typeset the book.
Note that the source code examples are just that—examples. While they will compile with the proper
compiler incantations, they are intended to illustrate the problem at hand, not necessarily serve as examples of good programming style.
This Book is Free
This book started out as bits of documentation written by Subversion project developers, which were
then coalesced into a single work and rewritten. As such, it has always had the same free, open-source
license as Subversion itself. In fact, the book was written in the public eye, as a part of Subversion. This
means two things:
You will always find the latest version of this book in Subversion's own source tree.
You can distribute and make changes to this book however you wish — it's under a free license. Of
course, rather than distribute your own private version of this book, we'd much rather you send feedback and patches to the Subversion developer community. See the section called “Contributing to
Subversion” to learn about joining this community.
You can send publishing comments and questions to O'Reilly here: ###insert boilerplate.
A relatively recent online version of this book can be found at
### Huge list of thanks to the many svn developers who sent patches/feedback on this book.
### Also, individual-author acknowledgments to specific friends and family.
Chapter 1. Introduction
Version control is the art of managing changes to information. It has long been a critical tool for programmers, who typically spend their time making small changes to software and then undoing those
changes the next day. Imagine a team of these programmers working concurrently, and you can see why
a good system is needed to manage the potential chaos.
What is Subversion?
Subversion is a free/open-source version control system. That is, Subversion manages files and directories over time. A tree of files is placed into a central repository. The repository is much like an ordinary
file server, except that it remembers every change ever made to your files and directories. This allows
you to recover older versions of your data, or examine the history of how your data changed. In this regard, many people think of a version control system as a sort of “time machine”.
Some version control systems are also software configuration management (SCM) systems. These systems are specifically tailored to manage trees of source code, and have many features that are specific to
software development—such as natively understanding programming languages, or supplying tools for
building software. Subversion, however, is not one of these systems; it is a general system that can be
used to manage any collection of files, including source code.
Subversion's History
In early 2000, CollabNet, Inc ( began seeking developers to write a replacement for CVS. CollabNet offers a collaboration software suite called SourceCast, of which one
component is version control. Although SourceCast used CVS as its initial version control system,
CVS's limitations were obvious from the beginning, and CollabNet knew it would eventually have to
find something better. Unfortunately, CVS had become the de facto standard in the open source world
largely because there wasn't anything better, at least not under a free license. So CollabNet determined
to write a new version control system from scratch, retaining the basic ideas of CVS, but without the
bugs and misfeatures.
In February 2000, they contacted Karl Fogel, the author of Open Source Development with CVS
(Coriolis, 1999), and asked if he'd like to work on this new project. Coincidentally, at the time Karl was
already discussing a design for a new version control system with his friend Jim Blandy. In 1995 the two
had started Cyclic Software, a company providing CVS support contracts, and although they later sold
the business, they still used CVS every day at their jobs. Their frustration with CVS had led Jim to think
carefully about better ways to manage versioned data, and he'd already come up with not only the name
"Subversion", but also with the basic design of the Subversion repository. When CollabNet called, Karl
immediately agreed to work on the project, and Jim got his employer, RedHat Software, to essentially
donate him to the project for an indefinite period of time. CollabNet hired Karl and Ben Collins-Sussman, and detailed design work began in May. With the help of some well-placed prods from Brian
Behlendorf and Jason Robbins of CollabNet, and Greg Stein (at the time an independent developer active in the WebDAV/DeltaV specification process), Subversion quickly attracted a community of active
developers. Many people had had frustrating experiences with CVS, and welcomed the chance to finally
do something about it.
The original design team settled on some simple goals. They didn't want to break new ground in version
control methodology, they just wanted to fix CVS. They decided that Subversion would match CVS's
features, and preserve the same development model, but not duplicate CVS's most obvious flaws. And
although it did not need to be a drop-in replacement for CVS, it should be similar enough that any CVS
user could make the switch with little effort.
After fourteen months of coding, Subversion became “self-hosting” on August 31, 2001. That is, Sub1
version developers stopped using CVS to manage Subversion's own source code, and started using Subversion instead.
While CollabNet started the project, and still funds a large chunk of the work (it pays the salaries of a
few full-time Subversion developers), Subversion is run like most open-source projects, governed by a
loose, transparent set of rules that encourage meritocracy. CollabNet's copyright license is fully compliant with the Debian Free Software Guidelines. In other words, anyone is free to download, modify, and
redistribute Subversion as he pleases; no permission from CollabNet or anyone else is required.
Subversion's Features
How does Subversion improve upon CVS's design? Here's a short list to whet your appetite. If you're not
familiar with CVS, you may not understand all of these features. Fear not: Chapter 2 will provide you
with a gentle introduction to version control.
Directory versioning
CVS only tracks the history of individual files, but Subversion
implements a “virtual” versioned filesystem that tracks changes to
whole directory trees over time. Files and directories are versioned. As a result, there are real client-side move and copy commands that operate on files and directories.
Atomic commits
A commit either goes into the repository completely, or not at all.
This allows developers to construct and commit changes as logical chunks.
Versioned metadata
Each file and directory has an invisible set of “properties” attached. You can invent and store any arbitrary key/value pairs you
wish. Properties are versioned over time, just like file contents.
Choice of network layers
Subversion has an abstracted notion of repository access, making
it easy for people to implement new network mechanisms. Subversion's “advanced” network server is a module for the Apache
web server, which speaks a variant of HTTP called WebDAV/
DeltaV. This gives Subversion a big advantage in stability and interoperability, and provides various key features for free: authentication, authorization, wire compression, and repository browsing, for example. A smaller, standalone Subversion server process
is also available. This server speaks a custom protocol which can
be easily tunneled over ssh.
Consistent data handling
Subversion expresses file differences using a binary differencing
algorithm, which works identically on both text (human-readable)
and binary (human-unreadable) files. Both types of files are
stored equally compressed in the repository, and differences are
transmitted in both directions across the network.
Efficient branching and tagging
The cost of branching and tagging need not be proportional to the
project size. Subversion creates branches and tags by simply
copying the project, using a mechanism similar to a hard-link.
Thus these operations take only a very small, constant amount of
Subversion has no historical baggage; it is implemented as a collection of shared C libraries with well-defined APIs. This makes
Subversion extremely maintainable and usable by other applications and languages.
Installing Subversion
Subversion is built on a portability layer called APR (the Apache Portable Runtime library). This means
Subversion should work on any operating system that the Apache httpd server runs on: Windows, Linux,
all flavors of BSD, Mac OS X, Netware, and others.
The easiest way to get Subversion is to download a binary package built for your operating system. Subversion's website ( often has binaries available for download,
posted by volunteers. The site usually contains graphical installer packages for users of Microsoft operating systems. If you run a Unix-like operating system, you can use your system's native packagedistribution system (rpm, deb, ports tree) to get Subversion.
Alternately, you can build Subversion directly from source code. From the website, you can download
the latest source-code release. After unpacking it, follow the instructions in the INSTALL file to build it.
Note that a released source package contains everything you need to build a command-line client capable of talking to a remote repository (in particular, the apr, apr-util, and neon libraries). But Subversion
has many other dependencies, such as Berkeley DB and possibly Apache httpd. If you want to do a
“full” build, make sure you have all of the packages documented in the INSTALL file. If you plan to
work on Subversion itself, you can use your client program to grab the latest, bleeding-edge source
code. This is documented in the section called “Get the Source Code”.
Subversion's Components
Subversion, once installed, has a number of different pieces. Here's a quick overview of what you get.
Client Components (for the User)
The command-line client program. This is the main tool used to manage data, and its
use is covered in Chapters 2, 3, 4, and 6.
A program for reporting the mixed-revision state of a working copy. (See Chapter 2,
Basic Concepts to understand mixed-revision working copies.)
Server Components (for the Administrator)
These are all discussed in Chapter 5, Repository Administration.
A tool for inspecting a Subversion repository.
A tool for creating, tweaking or repairing a Subversion repository.
A plug-in module for the Apache-2.X web server; used to make your repository
available to others over a network.
A standalone server program, runnable as a daemon process or invokable by SSH;
another way to make your repository available to others over a network.
Assuming you have Subversion installed correctly, you should be ready to start. The next two chapters
will walk you through the use of svn, Subversion's command-line client program.
Chapter 2. Basic Concepts
This chapter is a short, casual introduction to Subversion. If you're new to version control, this chapter is
definitely for you. We begin with a discussion of general version control concepts, work our way into
the specific ideas behind Subversion, and show some simple examples of Subversion in use.
Even though the examples in this chapter show people sharing collections of program source code, keep
in mind that Subversion can manage any sort of file collection—it's not limited to helping computer programmers.
The Repository
Subversion is a centralized system for sharing information. At its core is a repository, which is a central
store of data. The repository stores information in the form of a filesystem tree—a typical hierarchy of
files and directories. Any number of clients connect to the repository, and then read or write to these
files. By writing data, a client makes the information available to others; by reading data, the client receives information from others.
Figure 2.1. A Typical Client/Server System
So why is this interesting? So far, this sounds like the definition of a typical file server. And indeed, the
repository is a kind of file server, but it's not your usual breed. What makes the Subversion repository
special is that it remembers every change ever written to it: every change to every file, and even changes
to the directory tree itself, such as the addition, deletion, and rearrangement of files and directories.
When a client reads data from the repository, it normally sees only the latest version of the filesystem
tree. But the client also has the ability to view previous states of the filesystem. For example, a client can
Basic Concepts
ask historical questions like, "what did this directory contain last Wednesday?", or "who was the last
person to change this file, and what changes did they make?" These are the sorts of questions that are at
the heart of any version control system: systems that are designed to record and track changes to data
over time.
Versioning Models
The Problem of File-Sharing
All version control systems have to solve the same fundamental problem: how will the system allow
users to share information, but prevent them from accidentally stepping on each other's feet? It's all too
easy for users to accidentally overwrite each other's changes in the repository.
Consider this scenario: suppose we have two co-workers, Harry and Sally. They each decide to edit the
same repository file at the same time. If Harry saves his changes to the repository first, then it's possible
that (a few moments later) Sally could accidentally overwrite them with her own new version of the file.
While Harry's version of the file won't be lost forever (because the system remembers every change),
any changes Harry made won't be present in Sally's newer version of the file, because she never saw
Harry's changes to begin with. Harry's work is still effectively lost—or at least missing from the latest
version of the file—and probably by accident. This is definitely a situation we want to avoid!
Figure 2.2. The Problem to Avoid
The Lock-Modify-Unlock Solution
Basic Concepts
Many version control systems use a lock-modify-unlock model to address this problem, which is a very
simple solution. In such a system, the repository allows only one person to change a file at a time. First
Harry must "lock" the file before he can begin making changes to it. Locking a file is a lot like borrowing a book from the library; if Harry has locked a file, then Sally cannot make any changes to it. If she
tries to lock the file, the repository will deny the request. All she can do is read the file, and wait for
Harry to finish his changes and release his lock. After Harry unlocks the file, his turn is over, and now
Sally can take her turn by locking and editing.
Figure 2.3. The Lock-Modify-Unlock Solution
The problem with the lock-modify-unlock model is that it's a bit restrictive, and often becomes a roadblock for users:
Locking may cause administrative problems. Sometimes Harry will lock a file and then forget about
it. Meanwhile, because Sally is still waiting to edit the file, her hands are tied. And then Harry goes
on vacation. Now Sally has to get an administrator to release Harry's lock. The situation ends up
causing a lot of unnecessary delay and wasted time.
Locking may cause unnecessary serialization. What if Harry is editing the beginning of a text file,
and Sally simply wants to edit the end of the same file? These changes don't overlap at all. They
could easily edit the file simultaneously, and no great harm would come, assuming the changes were
properly merged together. There's no need for them to take turns in this situation.
Locking may create a false sense of security. Pretend that Harry locks and edits file A, while Sally
simultaneously locks and edits file B. But suppose that A and B depend on one another, and the
Basic Concepts
changes made to each are semantically incompatible. Suddenly A and B don't work together anymore. The locking system was powerless to prevent the problem—yet it somehow provided a false
sense of security. It's easy for Harry and Sally to imagine that by locking files, each is beginning a
safe, insulated task, and thus inhibits them from discussing their incompatible changes early on.
The Copy-Modify-Merge Solution
Subversion, CVS, and other version control systems use a copy-modify-merge model as an alternative to
locking. In this model, each user's client reads the repository and creates a personal working copy of the
file or project. Users then work in parallel, modifying their private copies. Finally, the private copies are
merged together into a new, final version. The version control system often assists with the merging, but
ultimately a human being is responsible for making it happen correctly.
Here's an example. Say that Harry and Sally each create working copies of the same project, copied
from the repository. They work concurrently, and make changes to the same file "A" within their copies.
Sally saves her changes to the repository first. When Harry attempts to save his changes later, the repository informs him that his file A is out-of-date. In other words, that file A in the repository has somehow
changed since he last copied it. So Harry asks his client to merge any new changes from the repository
into his working copy of file A. Chances are that Sally's changes don't overlap with his own; so once he
has both sets of changes integrated, he saves his working copy back to the repository.
Figure 2.4. The Copy-Modify-Merge Solution
Basic Concepts
Figure 2.5. …Copy-Modify-Merge Continued
But what if Sally's changes do overlap with Harry's changes? What then? This situation is called a conflict, and it's usually not much of a problem. When Harry asks his client to merge the latest repository
changes into his working copy, his copy of file A is somehow flagged as being in a state of conflict: he'll
be able to see both sets of conflicting changes, and manually choose between them. Note that software
can't automatically resolve conflicts; only humans are capable of understanding and making the necessary intelligent choices. Once Harry has manually resolved the overlapping changes (perhaps by discussing the conflict with Sally!), he can safely save the merged file back to the repository.
The copy-modify-merge model may sound a bit chaotic, but in practice, it runs extremely smoothly.
Users can work in parallel, never waiting for one another. When they work on the same files, it turns out
that most of their concurrent changes don't overlap at all; conflicts are infrequent. And the amount of
time it takes to resolve conflicts is far less than the time lost by a locking system.
In the end, it all comes down to one critical factor: user communication. When users communicate
poorly, both syntactic and semantic conflicts increase. No system can force users to communicate perfectly, and no system can detect semantic conflicts. So there's no point in being lulled into a false
promise that a locking system will somehow prevent conflicts; in practice, locking seems to inhibit productivity more than anything else.
Subversion in Action
Working Copies
Basic Concepts
You've already read about working copies; now we'll demonstrate how the Subversion client creates and
uses them.
A Subversion working copy is an ordinary directory tree on your local system, containing a collection of
files. You can edit these files however you wish, and if they're source code files, you can compile your
program from them in the usual way. Your working copy is your own private work area: Subversion will
never incorporate other people's changes, nor make your own changes available to others, until you explicitly tell it to do so.
After you've made some changes to the files in your working copy and verified that they work properly,
Subversion provides you with commands to "publish" your changes to the other people working with
you on your project (by writing to the repository). If other people publish their own changes, Subversion
provides you with commands to merge those changes into your working directory (by reading from the
A working copy also contains some extra files, created and maintained by Subversion, to help it carry
out these commands. In particular, each directory in your working copy contains a subdirectory named
.svn, also known as the working copy administrative directory. The files in each administrative directory help Subversion recognize which files contain unpublished changes, and which files are out-of-date
with respect to others' work.
A typical Subversion repository often holds the files (or source code) for several projects; usually, each
project is a subdirectory in the repository's filesystem tree. In this arrangement, a user's working copy
will usually correspond to a particular subtree of the repository.
For example, suppose you have a repository that contains two software projects.
Figure 2.6. The Repository's Filesystem
Basic Concepts
In other words, the repository's root directory has two subdirectories: paint and calc.
To get a working copy, you must check out some subtree of the repository. (The term "check out" may
sound like it has something to do with locking or reserving resources, but it doesn't; it simply creates a
private copy of the project for you.) For example, if you check out /calc, you will get a working copy
like this:
$ svn checkout
A calc
A calc/Makefile
A calc/integer.c
A calc/button.c
$ ls -a calc
Makefile integer.c
The list of letter A's indicates that Subversion is adding a number of items to your working copy. You
now have a personal copy of the repository's /calc directory, with one additional
entry—.svn—which holds the extra information needed by Subversion, as mentioned earlier.
Basic Concepts
Repository URLs
Subversion repositories can be accessed through many different methods—on local disk, or through various network protocols. A repository location, however, is always a URL. The URL schema indicates
the access method:
Table 2.1. Repository Access URLs
Access Method
direct repository access (on local disk)
access via WebDAV protocol to Subversion-aware
Apache server
same as http://, but with SSL encryption.
access via custom protocol to an svnserve
same as svn://, but through an SSH tunnel.
For the most part, Subversion's URLs use the standard syntax, allowing for server names and port numbers to be specified as part of the URL. Remember that the file: access method is valid only for locations on the same server as the client—in fact, in accordance with convention, the server name portion
of the URL is required to be either absent or localhost:
$ svn checkout file:///path/to/repos
$ svn checkout file://localhost/path/to/repos
Also, users of the file: scheme on Windows platforms will need to use an unofficially “standard”
syntax for accessing repositories that are on the same machine, but on a different drive than the client's
current working drive. Either of the two following URL path syntaxes will work where X is the drive on
which the repository resides:
C:\> svn checkout file:///X:/path/to/repos
C:\> svn checkout "file:///X|/path/to/repos"
In the second syntax, you need to quote the URL so that the vertical bar character is not interpreted as a
Note that a URL uses ordinary slashes even though the native (non-URL) form of a path on Windows
uses backslashes.
Suppose you make changes to button.c. Since the .svn directory remembers the file's modification
date and original contents, Subversion can tell that you've changed the file. However, Subversion does
not make your changes public until you explicitly tell it to. The act of publishing your changes is more
commonly known as committing (or checking in) changes to the repository.
To publish your changes to others, you can use Subversion's commit command:
Basic Concepts
$ svn commit button.c
Sending button.c
Transmitting file data..
Committed revision 57.
Now your changes to button.c have been committed to the repository; if another user checks out a
working copy of /calc, they will see your changes in the latest version of the file.
Suppose you have a collaborator, Sally, who checked out a working copy of /calc at the same time
you did. When you commit your change to button.c, Sally's working copy is left unchanged; Subversion only modifies working copies at the user's request.
To bring her project up to date, Sally can ask Subversion to update her working copy, by using the Subversion update command. This will incorporate your changes into her working copy, as well as any others that have been committed since she checked it out.
$ pwd
$ ls -a
.svn/ Makefile integer.c button.c
$ svn update
U button.c
The output from the svn update command indicates that Subversion updated the contents of button.c. Note that Sally didn't need to specify which files to update; Subversion uses the information in
the .svn directory, and further information in the repository, to decide which files need to be brought
up to date.
An svn commit operation can publish changes to any number of files and directories as a single atomic
transaction. In your working copy, you can change files' contents, create, delete, rename and copy files
and directories, and then commit the complete set of changes as a unit.
In the repository, each commit is treated as an atomic transaction: either all the commit's changes take
place, or none of them take place. Subversion tries to retain this atomicity in the face of program
crashes, system crashes, network problems, and other users' actions.
Each time the repository accepts a commit, this creates a new state of the filesystem tree, called a revision. Each revision is assigned a unique natural number, one greater than the number of the previous revision. The initial revision of a freshly created repository is numbered zero, and consists of nothing but
an empty root directory.
A nice way to visualize the repository is as a series of trees. Imagine an array of revision numbers, starting at 0, stretching from left to right. Each revision number has a filesystem tree hanging below it, and
each tree is a “snapshot” of the way the repository looked after each commit.
Figure 2.7. The Repository
Basic Concepts
Global Revision Numbers
Unlike those of many other version control systems, Subversion's revision numbers apply to entire trees,
not individual files. Each revision number selects an entire tree, a particular state of the repository after
some committed change. Another way to think about it is that revision N represents the state of the
repository filesystem after the Nth commit. When a Subversion user talks about ``revision 5 of foo.c'',
they really mean ``foo.c as it appears in revision 5.'' Notice that in general, revisions N and M of a file
do not necessarily differ! Because CVS uses per-file revisions numbers, CVS users might want to look
at Appendix A, "SVN for CVS Users", for more details.
It's important to note that working copies do not always correspond to any single revision in the repository; they may contain files from several different revisions. For example, suppose you check out a
working copy from a repository whose most recent revision is 4:
At the moment, this working directory corresponds exactly to revision 4 in the repository. However,
suppose you make a change to button.c, and commit that change. Assuming no other commits have
taken place, your commit will create revision 5 of the repository, and your working copy will now look
like this:
Basic Concepts
Suppose that, at this point, Sally commits a change to integer.c, creating revision 6. If you use svn
update to bring your working copy up to date, then it will look like this:
Sally's changes to integer.c will appear in your working copy, and your change will still be present
in button.c. In this example, the text of Makefile is identical in revisions 4, 5, and 6, but Subversion will mark your working copy of Makefile with revision 6 to indicate that it is still current. So, after you do a clean update at the top of your working copy, it will generally correspond to exactly one revision in the repository.
How Working Copies Track the Repository
For each file in a working directory, Subversion records two essential pieces of information in the
.svn/ administrative area:
what revision your working file is based on (this is called the file's working revision), and
a timestamp recording when the local copy was last updated by the repository.
Given this information, by talking to the repository, Subversion can tell which of the following four
states a working file is in:
Unchanged, and current
The file is unchanged in the working directory, and no changes to
that file have been committed to the repository since its working
revision. A svn commit of the file will do nothing, and an svn
update of the file will do nothing.
Locally changed, and current
The file has been changed in the working directory, and no
changes to that file have been committed to the repository since
its base revision. There are local changes that have not been committed to the repository, thus an svn commit of the file will succeed in publishing your changes, and an svn update of the file
will do nothing.
Unchanged, and out-of-date
The file has not been changed in the working directory, but it has
been changed in the repository. The file should eventually be updated, to make it current with the public revision. An svn commit
of the file will do nothing, and an svn update of the file will fold
the latest changes into your working copy.
Locally changed, and out-of-date
The file has been changed both in the working directory, and in
the repository. An svn commit of the file will fail with an "outof-date" error. The file should be updated first; an svn update
command will attempt to merge the public changes with the local
changes. If Subversion can't complete the merge in a plausible
way automatically, it leaves it to the user to resolve the conflict.
Basic Concepts
This may sound like a lot to keep track of, but the svn status command will show you the state of any
item in your working copy. For more information on that command, see the section called “svn status”.
The Limitations of Mixed Revisions
As a general principle, Subversion tries to be as flexible as possible. One special kind of flexibility is the
ability to have a working copy containing mixed revision numbers.
At first, it may not be entirely clear why this sort of flexibility is considered a feature, and not a liability.
After completing a commit to the repository, the freshly committed files and directories are at more recent working revision than the rest of the working copy. It looks like a bit of a mess. As demonstrated
earlier, the working copy can always be brought to a single working revision by running svn update.
Why would someone deliberately want a mixture of working revisions?
Assuming your project is sufficiently complex, you'll discover that it's sometimes nice to forcibly back“date” portions of your working copy to an earlier revision; you'll learn how to do that in Chapter 3. Perhaps you'd like to test an earlier version of a sub-module, contained in a subdirectory, or perhaps you'd
like to examine a number of previous versions of a file in the context of the latest tree.
However you make use of mixed-revisions in your working copy, there are limitations to this flexibility.
First, you cannot commit the deletion of a file or directory which isn't fully up-to-date. If a newer version of the item exists in the repository, your attempt to delete will be rejected, to prevent you from accidentally destroying changes you've not yet seen.
Second, you cannot commit a metadata change to a directory unless it's fully up-to-date. You'll learn
about attaching “properties” to items in Chapter 6. A directory's working revision defines a specific set
of entries and properties, and thus committing a property change to an out-of-date directory may destroy
properties you've not yet seen.
We've covered a number of fundamental Subversion concepts in this chapter:
We've introduced the notions of the central repository, the client working copy, and the array of
repository revision trees.
We've seen some simple examples of how two collaborators can use Subversion to publish and receive changes from one another, using the 'copy-modify-merge' model.
We've talked a bit about the way Subversion tracks and manages information in a working copy.
At this point, you should have a good idea of how Subversion works in the most general sense. Armed
with this knowledge, you should now be ready to jump into the next chapter, which is a detailed tour of
Subversion's commands and features.
Chapter 3. Guided Tour
Now we will go into the details of using Subversion. By the time you reach the end of this chapter, you
will be able to perform almost all the tasks you need to use Subversion in a normal day's work. You'll
start with an initial checkout of your code, and walk through making changes and examining those
changes. You'll also see how to bring changes made by others into your working copy, examine them,
and work through any conflicts that might arise.
Note that this chapter is not meant to be an exhaustive list of all Subversion's commands—rather, it's a
conversational introduction to the most common Subversion tasks you'll encounter. This chapter assumes that you've read and understood Chapter 2, Basic Concepts and are familiar with the general
model of Subversion. For a complete reference of all commands, see Chapter 9, Subversion Complete
Before reading on, here is the most important command you'll ever need when using Subversion: svn
help. The Subversion command-line client is self-documenting—at any time, a quick svn help sub<command> will describe the syntax, switches, and behavior of the subcommand.
You use svn import to import a new project into a Subversion repository. While this is most likely the
very first thing you will do when you set up your Subversion server, it's not something that happens very
often. For a detailed description of import, see the section called “svn import” later in this chapter.
Revisions: Numbers, Keywords, and Dates, Oh
Before we go on, you should know a bit about how to identify a particular revision in your repository.
As you learned in the section called “Revisions”, a revision is a “snapshot” of the repository at a particular moment in time. As you continue to commit and grow your repository, you need a mechanism for
identifying these snapshots.
You specify these revisions by using the --revision (-r) switch plus the revision you want (svn -revision REV) or you can specify a range by separating two revisions with a colon (svn --revision
REV1:REV2). And Subversion lets you refer to these revisions by number, keyword, or date.
Revision Numbers
When you create a new Subversion repository, it begins its life at revision zero and each successive
commit increases the revision number by one. After your commit completes, the Subversion client informs you of the new revision number:
$ svn commit --message "Corrected number of cheese slices."
Transmitting file data .
Committed revision 3.
If at any point in the future you want to refer to that revision (we'll see how and why we might want to
Guided Tour
do that later in this chapter), you can refer to it as “3”.
Revision Keywords
The Subversion client understands a number of revision keywords. These keywords can be used instead
of integer arguments to the --revision switch, and are resolved into specific revision numbers by
Each directory in your working copy contains an .svn administrative area. For every file in a
directory, Subversion keeps a copy of each file in the administrative area. This copy is an unmodified (no keyword expansion, no end-of-line translation, no nothing) copy of the file as it
existed in the last revision (called the “BASE” revision) that you updated it to in your working
copy. We refer to this file as a “pristine” copy.
The latest revision in the repository.
The “pristine” revision of an item in a working copy.
COMMITTED The last revision in which an item changed before (or at) BASE.
The revision just before the last revision in which an item changed. (Technically, COMMITTED - 1.)
Here are some examples of revision keywords in action (don't worry if the commands don't make sense
yet; we'll be explaining these commands as we go through the chapter):
$ svn diff --revision PREV:COMMITTED foo.c
# shows the last change committed to foo.c
$ svn log --revision HEAD
# shows log message for the latest repository commit
$ svn diff --revision HEAD
# compares your working file (with local mods) to the latest version
# in the repository.
$ svn diff --revision BASE:HEAD foo.c
# compares your “pristine” foo.c (no local mods) with the
# latest version in the repository
$ svn log --revision BASE:HEAD
# shows all commit logs since you last updated
$ svn update --revision PREV foo.c
# rewinds the last change on foo.c.
# (foo.c's working revision is decreased.)
These keywords allow you to perform many common (and helpful) operations without having to look up
specific revision numbers or remember the exact revision of your working copy.
Revision Dates
Anywhere that you specify a revision number or revision keyword, you can also specify a date by speci17
Guided Tour
fying the date inside curly braces “{}”. You can even access a range of changes in the repository using
both dates and revisions together!
Here are examples of the date formats that Subversion accepts. Remember to use quotes around any date
that contains spaces.
{"2002-02-17 15:30"}
{"2002-02-17 15:30 +0230"}
When you specify a date as a revision, Subversion finds the most recent revision of the repository as of
that date:
$ svn log --revision {2002-11-28}
-----------------------------------------------------------------------r12 | ira | 2002-11-27 12:31:51 -0600 (Wed, 27 Nov 2002) | 6 lines
Is Subversion a Day Early?
If you specify a single date as a revision without specifying a time of day (for example 2002-11-27),
you may think that Subversion should give you the last revision that took place on the 27th of November. Instead, you'll get back a revision from the 26th, or even earlier. Remember that Subversion will
find the most recent revision of the repository as of the date you give. If you give a date without a timestamp, like 2002-11-27, Subversion assumes a time of 00:00:00, so looking for the most recent revision won't return anything on the day of the 27th.
If you want to include the 27th in your search, you can either specify the 27th with the time ( 23:59"),
or just specify the next day (2002-11-28).
You can also use a range of dates. Subversion will find all revisions between both dates, inclusive:
$ svn log --revision {2002-11-20}:{2002-11-29}
As we pointed out, you can also mix dates and revisions:
$ svn log --revision {2002-11-20}:4040
Guided Tour
Initial Checkout
Most of the time, you will start using a Subversion repository by doing a checkout of your project.
“Checking out” a repository creates a copy of it on your local machine. This copy contains the HEAD
(latest revision) of the Subversion repository that you specify on the command line:
$ svn checkout
A trunk/subversion.dsw
A trunk/svn_check.dsp
A trunk/
A trunk/IDEAS
Checked out revision 2499.
Repository Layout
If you're wondering what trunk is all about in the above URL, it's part of the way we recommend you
lay out your Subversion repository which we'll talk a lot more about in Chapter 4, Branching and Merging.
Although the above example checks out the trunk directory, you can just as easily check out any deep
subdirectory of a repository by specifying the subdirectory in the checkout URL:
$ svn checkout
A tools/readme-dblite.html
A tools/fo-stylesheet.xsl
A tools/svnbook.el
A tools/dtd
A tools/dtd/dblite.dtd
Checked out revision 3678.
Since Subversion uses a “copy-modify-merge” model instead of “lock-modify-unlock” (see Chapter 2,
Basic Concepts), you're now ready to start making changes to the files and directories that you've
checked out (known collectively as your working copy).
In other words, your “working copy” is now just like any other collection of files and/or directories on
your system1. You can edit and change them, move them around, you can even delete the entire working
copy and forget about it.
While your working copy is “just like any other collection of files and directories on your system”, you need to let Subversion know if you're going to be rearranging anything inside of your
working copy. If you want to copy or move an item in a working copy, you should use svn
copy or svn move instead of the copy and move commands provided by your operating system.
We'll talk more about them later in this chapter.
Unless you're ready to commit a new file or directory, or changes to existing ones, there's no need to fur1
Well, except for the fact that every directory within your “working copy” also contains a .svn subdirectory. But that's getting a
little ahead of ourselves.
Guided Tour
ther notify the Subversion server that you've done anything.
What's with the .svn directory?
Every directory in a working copy contains an administrative area, a subdirectory named .svn. Usually, directory listing commands won't show this subdirectory, but it is nevertheless an important directory. Whatever you do, don't delete or change anything in the administrative area! Subversion depends
on it to manage your working copy.
While you can certainly check out a working copy with the URL of the repository as the only argument,
you can also specify a directory after your repository URL. This places your working copy into the new
directory that you name. For example:
$ svn checkout subv
A subv/subversion.dsw
A subv/svn_check.dsp
A subv/
A subv/IDEAS
Checked out revision 2499.
That will place your working copy in a directory named subv instead of a directory named trunk as
we did previously.
Basic Work Cycle
Subversion has numerous features, options, bells and whistles, but on a day-to-day basis, odds are that
you will only use a few of them. In this section we'll run through the most common things that you
might find yourself doing with Subversion in the course of a day's work.
The typical work cycle looks like this:
Update your working copy
svn update
Make changes
svn add
svn delete
svn copy
svn move
Examine your changes
Guided Tour
svn status
svn diff
svn revert
Merge others' changes
svn merge
svn resolved
Commit your changes
svn commit
Update Your Working Copy
When working on a project with a team, you'll want to update your working copy: that is, receive any
changes from other developers on the project. You'll use svn update to bring your working copy into
sync with the latest revision in the repository.
$ svn update
U ./foo.c
U ./bar.c
Updated to revision 2.
In this case, someone else checked in modifications to both foo.c and bar.c since the last time you
updated, and Subversion has updated your working copy to include those changes.
Let's examine the output of svn update a bit more. When the server sends changes to your working
copy, a letter code is displayed next to each item to let you know what actions Subversion performed to
bring your working copy up-to-date:
U foo
File foo was Updated (received changes from the server).
A foo
File or directory foo was Added to your working copy.
D foo
File or directory foo was Deleted from your working copy.
R foo
File or directory foo was Replaced in your working copy; that is, foo was deleted,
and a new item with the same name was added. While they may have the same name,
the repository considers them to be distinct objects with distinct histories.
G foo
File foo received new changes from the repository, but your local copy of the file had
your modifications. The changes did not intersect, however, so Subversion has merGed
the repository's changes into the file without a problem.
C foo
File foo received Conflicting changes from the server. The changes from the server
Guided Tour
directly overlap your own changes to the file. No need to panic, though. This overlap
needs to be resolved by a human (you); we discuss this situation later in this chapter.
Make Changes to Your Working Copy
Now you can get to work and make changes in your working copy. It's usually most convenient to decide on a particular change (or set of changes) to make, such as writing a new feature, fixing a bug, etc.
The Subversion commands that you will use here are svn add, svn delete, svn copy, and svn move.
However, if you are merely editing a file (or files) that is already in Subversion, you may not need to use
any of these commands until you commit. Changes you can make to your working copy:
File changes
This is the simplest sort of change. You don't need to tell Subversion that you intend
to change a file; just make your changes. Subversion will be able to automatically
detect which files have been changed.
Tree changes
You can ask Subversion to “mark” files and directories for scheduled removal, addition, copying, or moving. While these changes may take place immediately in your
working copy, no additions or removals will happen in the repository until you
commit them.
To make file changes, use your text editor, word processor, graphics program, or whatever tool you
would normally use. Subversion handles binary files just as easily as it handles text files—and just as efficiently too.
Here is an overview of the four Subversion subcommands that you'll use most often to make tree
changes (we'll cover svn import and svn mkdir later).
svn add foo
Schedule foo to be added to the repository. When you next commit, foo
will become a child of its parent directory. Note that if foo is a directory, everything underneath foo will be scheduled for addition. If you only want to
schedule foo itself, pass the --non-recursive (-N) switch.
svn delete foo
Schedule foo to be deleted from the repository. If foo is a file, it is immediately deleted from your working copy. If foo is a directory, it is not deleted,
but Subversion schedules it for deletion. When you commit your changes,
foo will be removed from your working copy and the repository. 2
svn copy foo bar
Create a new item bar as a duplicate of foo. bar is automatically scheduled
for addition. When bar is added to the repository on the next commit, its
copy-history is recorded (as having originally come from foo).
svn move foo bar
This command is exactly the same as running svn copy foo bar; svn delete
foo. That is, bar is scheduled for addition as a copy of foo, and foo is
scheduled for removal.
Changing the Repository Without a Working Copy
Earlier in this chapter, we said that you have to commit any changes that you make in order for the
repository to reflect these changes. That's not entirely true—there are some use-cases that immediately
commit tree changes to the repository. This only happens when a subcommand is operating directly on a
URL, rather than on a working-copy path. In particular, specific uses of svn mkdir, svn copy, svn
2move, and svn delete can work with URLs.
Of course, nothing is ever totally deleted from the repository—just from the HEAD of the repository. You can get back anything
you delete by checking out (or updating your working copy) a revision earlier than the one in which you deleted it.
Guided Tour
URL operations behave in this manner because commands that operate on a working copy can use the
working copy as a sort of “staging area” to set up your changes before committing them to the repository. Commands that operate on URLs don't have this luxury, so when you operate directly on a URL,
any of the above actions represent an immediate commit.
Examine Your Changes
Once you've finished making changes, you need to commit them to the repository, but before you do so,
it's usually a good idea to take a look at exactly what you've changed. By examining your changes before you commit, you can make a more accurate log message. You may also discover that you've inadvertently changed a file, and this gives you a chance to revert those changes before committing. Additionally, this is a good opportunity to review and scrutinize changes before publishing them. You can see
exactly what changes you've made by using svn status, svn diff, and svn revert. You will usually use
the first two commands to find out what files have changed in your working copy, and then perhaps the
third to revert some (or all) of those changes.
Subversion has been optimized to help you with this task, and is able to do many things without communicating with the repository. In particular, your working copy contains a secret cached “pristine” copy of
each version controlled file within the .svn area. Because of this, Subversion can quickly show you
how your working files have changed, or even allow you to undo your changes without contacting the
svn status
You'll probably use the svn status command more than any other Subversion command.
CVS Users: Hold That Update!
You're probably used to using cvs update to see what changes you've made to your working copy. svn
status will give you all the information you need regarding what has changed in your working
copy—without accessing the repository or potentially incorporating new changes published by other
In Subversion, update does just that—it updates your working copy with any changes committed to the
repository since the last time you've updated your working copy. You'll have to break the habit of using
the update command to see what local modifications you've made.
If you run svn status at the top of your working copy with no arguments, it will detect all file and tree
changes you've made. This example is designed to show all the different status codes that svn status can
return. The text following # is not printed by svn status.
$ svn status
A +
M +
svn has a lock in its .svn directory for abc.c
the content in bar.c has local modifications
baz.c has property but no content modifications
svn doesn't manage foo.o
svn manages this, but it's either missing or incompl
versioned as dir, but is file, or vice versa
added with history of where it came from
added with history and has local modifications
this file is scheduled for deletion
this file is scheduled for addition
this file has conflicts from an update
Guided Tour
# this file or dir has been switched to a branch
In this output format svn status prints five columns of characters, followed by several whitespace characters, followed by a file or directory name. The first column tells the status of a file or directory and/or
its contents. The codes printed here are:
A file_or_dir
The file or directory file_or_dir has been scheduled for addition into
the repository.
C file
file_or_dir is in a state of conflict. That is, changes received from the
server during an update overlap with local changes that you have in your
working copy. You must resolve this conflict before committing your
changes to the repository.
D file_or_dir
The file or directory file_or_dir has been scheduled for deletion from
the repository.
M file
The contents of file file have been modified.
X dir
The directory dir is unversioned, but is related to a Subversion externals
definition. To find out more about externals definitions, see the section
called “Externals Definitions”.
? file_or_dir
The file or directory file_or_dir is not under version control. You can
silence the question marks by either passing the --quiet (-q) switch to
svn status, or by setting the svn:ignore property on the parent directory. For more information on ignored files, see the section called
! file_or_dir
The file or directory file_or_dir is under version control but is missing or somehow incomplete. The item can be missing if it's removed using
a non-Subversion command. In the case of a directory, it can be incomplete if you happened to interrupt a checkout or update. A quick svn update will refetch the file or directory from the repository, or svn revert file
will restore a missing file.
~ file_or_dir
The file or directory file_or_dir is in the repository as one kind of object, but what's actually in your working copy is some other kind. For example, Subversion might have a file in the repository, but you removed the
file and created a directory in its place, without using the svn delete or svn
add commands.
The second column tells the status of a file or directory's properties (see the section called “Properties”
for more information on properties). If an M appears in the second column, then the properties have been
modified, otherwise a whitespace will be printed.
The third column will only show whitespace or an L which means that Subversion has locked the item in
the .svn working area. You will see an L if you run svn status in a directory where an svn commit is
in progress—perhaps when you are editing the log message. If Subversion is not running, then presumably Subversion was interrupted and the lock needs to be cleaned up by running svn cleanup (more
about that later in this chapter).
The fourth column will only show whitespace or a + which means that the file or directory is scheduled
to be added or modified with additional attached history. This typically happens when you svn move or
svn copy a file or directory. If you see A +, this means the item is scheduled for addition-with-history.
It could be a file, or the root of a copied directory. + means the item is part of a subtree scheduled for
Guided Tour
addition-with-history, i.e. some parent got copied, and it's just coming along for the ride. M + means
the item is part of a subtree scheduled for addition-with-history, and it has local modifications. When
you commit, first the parent will be added-with-history (copied), which means this file will automatically exist in the copy. Then the local modifications will be uploaded into the copy.
The fifth column will only show whitespace or an S. This signifies that the file or directory has been
switched from the path of the rest of the working copy (using svn switch) to a branch.
If you pass a specific path to svn status, it gives you information about that item alone:
$ svn status stuff/fish.c
svn status also has a --verbose (-v) switch, which will show you the status of every item in your
working copy, even if it has not been changed:
$ svn status --verbose
This is the “long form” output of svn status. The first column remains the same, but the second column
shows the working-revision of the item. The third and fourth columns show the revision in which the
item last changed, and who changed it.
None of the above invocations to svn status contact the repository, they work only locally by comparing
the metadata in the .svn directory with the working copy. Finally, there is the --show-updates (u) switch, which contacts the repository and adds information about things that are out-of-date:
$ svn status --show-updates --verbose
Notice the two asterisks: if you were to run svn update at this point, you would receive changes to
README and trout.c. This tells you some very useful information—you'll need to update and get the
server changes on README before you commit, or the repository will reject your commit for being outof-date. (More on this subject later.)
svn diff
Another way to examine your changes is with the svn diff command. You can find out exactly how
you've modified things by running svn diff with no arguments, which prints out file changes in unified
diff format:3
Guided Tour
$ svn diff
Index: ./bar.c
--- ./bar.c
+++ ./bar.c Mon Jul 15 17:58:18 2002
@@ -1,7 +1,12 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <stdio.h>
int main(void) {
printf("Sixty-four slices of American Cheese...\n");
printf("Sixty-five slices of American Cheese...\n");
return 0;
Index: ./README
--- ./README
+++ ./README Mon Jul 15 17:58:18 2002
@@ -193,3 +193,4 @@
+Note to self: pick up laundry.
Index: ./stuff/fish.c
--- ./stuff/fish.c
+++ ./stuff/fish.c Mon Jul 15 17:58:18 2002
-Welcome to the file known as 'fish'.
-Information on fish will be here soon.
Index: ./stuff/things/bloo.h
--- ./stuff/things/bloo.h
+++ ./stuff/things/bloo.h Mon Jul 15 17:58:18 2002
+Here is a new file to describe
+things about bloo.
The svn diff command produces this output by comparing your working files against the cached pris“tine” copies within the .svn area. Files scheduled for addition are displayed as all added-text, and files
scheduled for deletion are displayed as all deleted text.
Output is displayed in unified diff format. That is, removed lines are prefaced with a - and added lines
are prefaced with a +. svn diff also prints filename and offset information useful to the patch program,
so you can generate “patches” by redirecting the diff output to a file:
$ svn diff > patchfile
You could, for example, email the patchfile to another developer for review or testing prior to commit.
svn revert
Subversion uses its internal diff engine, which produces unified diff format, by default. If you want diff output in a different format, specify an external diff program using --diff-cmd and pass any flags you'd like to it using the --extensions switch.
For example, to see local differences in file foo.c in context output format while ignoring whitespace changes, you might run
“svn diff --diff-cmd /usr/bin/diff --extensions '-bc' foo.c”.
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Now suppose you see the above diff output, and realize that your changes to README are a mistake;
perhaps you accidentally typed that text into the wrong file in your editor.
This is a perfect opportunity to use svn revert.
$ svn revert README
Reverted ./README
Subversion reverts the file to its pre-modified state by overwriting it with the cached “pristine” copy
from the .svn area. But also note that svn revert can undo any scheduled operations—for example,
you might decide that you don't want to add a new file after all:
$ svn status foo
$ svn add foo
$ svn revert foo
Reverted foo
$ svn status foo
svn revert ITEM has exactly the same effect as deleting ITEM from your working copy and
then running svn update ITEM. However, if you're reverting a file, svn revert has one very
noticeable difference—it doesn't have to communicate with the repository to restore your file.
Or perhaps you mistakenly removed a file from version control:
$ svn status README
$ svn delete README
$ svn revert README
Reverted README
$ svn status README
Look Ma! No Network!
All three of these commands (svn status, svn diff, and svn revert) can be used without any network access. This makes it easy to manage your changes-in-progress when you are somewhere without a network connection, such as traveling on an airplane, riding a commuter train or hacking on the beach.
Subversion does this by keeping private caches of pristine versions of each versioned file inside of the
Guided Tour
.svn administrative areas. This allows Subversion to report—and revert—local modifications to those
files without network access. This cache (called the "text-base") also allows Subversion to send the
user's local modifications during a commit to the server as a compressed delta against the pristine version. Having this cache is a tremendous benefit—even if you have a fast net connection, it's much faster
to send only a file's changes rather than the whole file to the server. At first glance, this might not seem
that important, but imagine the repercussions if you try to commit a one line change to a 400MB file and
have to send the whole file to the server!
Resolve Conflicts (Merging Others' Changes)
We've already seen how svn status -u can predict conflicts. Suppose you run svn update and some interesting things occur:
$ svn update
C ./bar.c
The U and G codes are no cause for concern; those files cleanly absorbed changes from the repository.
The files marked with U contained no local changes but were Updated with changes from the repository.
The G stands for merGed, which means that the file had local changes to begin with, but the changes
coming from the repository didn't overlap in any way.
But the C stands for conflict. This means that the changes from the server overlapped with your own,
and now you have to manually choose between them.
Whenever a conflict occurs, your Subversion client does three things:
Subversion prints a C during the update, and remembers that the file is “conflicted”.
Subversion places conflict markers into the file to visibly demonstrate the overlapping areas.
For every conflicted file, Subversion places three extra files in your working copy:
This is your file as it existed in your working copy before you updated
your working copy—that is, without conflict markers. This file has your
latest changes in it and nothing else.
This is the file that was the BASE revision before you updated your working copy. That is, the file that you checked out before you made your latest edits.
This is the file that your Subversion client just received from the server
when you updated your working copy. This file corresponds to the HEAD
revision of the repository.
Here OLDREV is the revision number of the file in your .svn directory and NEWREV is the revision
number of the repository HEAD.
For example, Sally makes changes to the file sandwich.txt in the repository. Harry has just changed
the file in his working copy and checked it in. Sally updates her working copy before checking in and
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she gets a conflict:
$ svn update
C sandwich.txt
Updated to revision 2.
$ ls -1
At this point, Subversion will not allow you to commit the file sandwich.txt until the three temporary files are removed.
$ svn commit --message "Add a few more things"
svn: A conflict in the working copy obstructs the current operation
svn: Commit failed (details follow):
svn: Aborting commit: '/home/sally/svn-work/sandwich.txt' remains in conflict.
If you get a conflict, you need to do one of three things:
Merge the conflicted text “by hand” (by examining and editing the conflict markers within the file).
Copy one of the temporary files on top of your working file.
Run svn revert <filename> to throw away all of your local changes.
Once you've resolved the conflict, you need to let Subversion know by running svn resolved. This removes the three temporary files and Subversion no longer considers the file to be in a state of conflict.4
$ svn resolved sandwich.txt
Resolved conflicted state of sandwich.txt
Merging Conflicts by Hand
Merging conflicts by hand can be quite intimidating the first time you attempt it, but with a little practice, it can become as easy as falling off a bike.
Here's an example. Let's say that, due to a miscommunication between you and your collaborator, Sally,
both edit the file named sandwich.txt at the same time. Sally commits her changes, and when you
go to update your working copy, you get a conflict and we're going to have to edit sandwich.txt to
resolve the conflicts. First, let's take a look at the file:
$ cat sandwich.txt
Top piece of bread
You can always remove the temporary files yourself, but would you really want to do that when Subversion can do it for you?
We didn't think so.
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<<<<<<< .mine
Grilled Chicken
>>>>>>> .r2
Creole Mustard
Bottom piece of bread
The strings of less-than signs, equal signs, and greater-than signs are called conflict markers. The text
between the first two sets of markers is composed of the changes you made in the conflicting area:
<<<<<<< .mine
Whereas the text between the second and third sets of conflict markers is the text from Sally's commit:
Grilled Chicken
>>>>>>> .r2
Usually you won't want to just delete the conflict markers and Sally's changes—she's going to be awfully surprised when the sandwich arrives and it's not what she wanted. So this is where you pick up the
phone or walk across the office and explain to Sally that you can't get sauerkraut from an Italian deli.5
Once you've agreed on the changes you will check in, edit your file and remove the conflict markers.
Top piece of bread
Creole Mustard
Bottom piece of bread
Now run svn resolved and you're now ready to commit your changes:
$ svn resolved sandwich.txt
$ svn commit -m "Go ahead and use my sandwich, discarding Sally's edits."
Remember, if you ever get confused while editing the conflicted file, you can always consult the three
And if you ask them for it, they may very well ride you out of town on a rail.
Guided Tour
files that Subversion creates for you in your working copy—including your file as it was before you updated.
Copying a File Onto Your Working File
If you get a conflict and decide that you want to throw out your changes, you can merely copy one of the
temporary files created by Subversion over the file in your working copy:
$ svn update
C sandwich.txt
Updated to revision 2.
$ ls sandwich.*
sandwich.txt sandwich.txt.mine sandwich.txt.r2
$ cp sandwich.txt.r2 sandwich.txt
$ svn resolved sandwich.txt
Punting: Using svn revert
If you get a conflict, and upon examination decide that you want to throw out your changes and start
your edits again, just revert your changes:
$ svn revert sandwich.txt
Reverted sandwich.txt
$ ls sandwich.*
Note that when you revert a conflicted file, you don't have to run svn resolved.
Now you're ready to check in your changes. Note that svn resolved, unlike most of the other commands
we've dealt with in this chapter, requires an argument. In any case, you want to be careful and only run
svn resolved when you're certain that you've fixed the conflict in your file—once the temporary files are
removed, Subversion will let you commit the file even if it still contains conflict markers.
Commit Your Changes
Finally! Your edits are finished, you've merged all changes from the server, and you're ready to commit
your changes to the repository.
The svn commit command sends all of your changes to the repository. When you commit a change, you
need to supply a log message, describing your change. Your log message will be attached to the new revision you create. If your log message is brief, you may wish to supply it on the command line using the
--message (or -m) option:
$ svn commit --message "Corrected number of cheese slices."
Transmitting file data .
Committed revision 3.
However, if you've been composing your log message as you work, you may want to tell Subversion to
get the message from a file by passing the filename with the --file switch:
Guided Tour
svn commit --file logmsg
Transmitting file data .
Committed revision 4.
If you fail to specify either the --message or --file switch, then Subversion will automatically
launch your favorite editor (as defined in the environment variable $EDITOR) for composing a log message.
If you're in your editor writing a commit message and decide that you want to cancel your commit, you can just quit your editor without saving changes. If you've already saved your commit
message, simply delete the text and save again.
$ svn commit
Waiting for Emacs...Done
Log message unchanged or not specified
a)bort, c)ontinue, e)dit
The repository doesn't know or care if your changes make any sense as a whole; it only checks to make
sure that nobody else has changed any of the same files that you did when you weren't looking. If somebody has done that, the entire commit will fail with a message informing you that one or more of your
files is out-of-date:
$ svn commit --message "Add another rule"
svn: Transaction is out of date
svn: Commit failed (details follow):
svn: out of date: `rules.txt' in txn `g'
At this point, you need to run svn update, deal with any merges or conflicts that result, and attempt your
commit again.
That covers the basic work cycle for using Subversion. There are many other features in Subversion that
you can use to manage your repository and working copy, but you can get by quite easily using only the
commands that we've discussed so far in this chapter.
Examining History
As we mentioned earlier, the repository is like a time machine. It keeps a record of every change ever
committed, and allows you to explore this history by examining previous versions of files and directories as well as the metadata that accompanies them. With a single Subversion command, you can check
out the repository (or restore an existing working copy) exactly as it was at any date or revision number
in the past. However, sometimes you just want to peer into the past instead of going into the past.
There are several commands that can provide you with historical data from the repository:
Guided Tour
svn log
Shows you broad information: log messages attached to revisions, and which paths
changed in each revision.
svn diff
Shows you the specific details of how a file changed over time.
svn cat
This is used to retrieve any file as it existed in a particular revision number and display it
on your screen.
svn list
Displays the files in a directory for any given revision.
svn log
To find out information about the history of a file or directory, use the svn log command. svn log will
provide you with a record of who made changes to a file or directory, at what revision it changed, the
time and date of that revision, and, if it was provided, the log message that accompanied the commit.
$ svn log
-----------------------------------------------------------------------r3 | sally | Mon, 15 Jul 2002 18:03:46 -0500 | 1 line
Added include lines and corrected # of cheese slices.
-----------------------------------------------------------------------r2 | harry | Mon, 15 Jul 2002 17:47:57 -0500 | 1 line
Added main() methods.
-----------------------------------------------------------------------r1 | sally | Mon, 15 Jul 2002 17:40:08 -0500 | 2 lines
Initial import
Note that the log messages are printed in reverse chronological order by default. If you wish to see a
different range of revisions in a particular order, or just a single revision, pass the --revision (-r)
$ svn log --revision 5:19
# shows logs 5 through 19 in chronological order
$ svn log -r 19:5
# shows logs 5 through 19 in reverse order
$ svn log -r 8
# shows log for revision 8
You can also examine the log history of a single file or directory. For example:
$ svn log foo.c
$ svn log
These will display log messages only for those revisions in which the working file (or URL) changed.
If you want even more information about a file or directory, svn log also takes a --verbose (-v)
Guided Tour
switch. Because Subversion allows you to move and copy files and directories, it is important to be able
to track path changes in the filesystem, so in verbose mode, svn log will include a list of changed-paths
in a revision in its output:
$ svn log -r 8 -v
-----------------------------------------------------------------------r8 | sally | 2002-07-14 08:15:29 -0500 | 1 line
Changed paths:
U /trunk/code/foo.c
U /trunk/code/bar.h
A /trunk/code/doc/README
Frozzled the sub-space winch.
Why Does svn log Give Me an Empty Response?
After working with Subversion for a bit, most users will come across something like this:
$ svn log -r 2
At first glance, this seems like an error, but you need to remember that while revisions are repositorywide, svn log operates on a path in the repository (if you supply no path, Subversion defaults to ".").
As a result, if you're operating in a subdirectory of your working copy and attempt to log a revision
where nothing beneath your current directory changed, Subversion will give you an empty log. If you
want to see what changed in that revision, try running the same command from the top directory of your
working copy.
svn diff
We've already seen svn diff before—it displays file differences in unified diff format; it was used to
show the local modifications made to our working copy before committing to the repository.
In fact, it turns out that there are three distinct uses of svn diff:
Examine local changes
Compare your working copy to the repository
Compare repository to repository
Examining Local Changes
As we've seen, invoking svn diff with no switches will compare your working files to the cached pris“tine” copies in the.svn area:
$ svn diff
Guided Tour
Index: rules.txt
--- rules.txt (revision 3)
+++ rules.txt (working copy)
@@ -1,4 +1,5 @@
Be kind to others
Freedom = Responsibility
Everything in moderation
-Chew with your mouth open
+Chew with your mouth closed
+Listen when others are speaking
Comparing Working Copy to Repository
If a single --revision (-r) number is passed, then your working copy is compared to the specified
revision in the repository.
$ svn diff --revision 3 rules.txt
Index: rules.txt
--- rules.txt (revision 3)
+++ rules.txt (working copy)
@@ -1,4 +1,5 @@
Be kind to others
Freedom = Responsibility
Everything in moderation
-Chew with your mouth open
+Chew with your mouth closed
+Listen when others are speaking
Comparing Repository to Repository
If two revision numbers, separated by a colon, are passed via --revision (-r), then the two revisions are directly compared.
$ svn diff --revision 2:3 rules.txt
Index: rules.txt
--- rules.txt (revision 2)
+++ rules.txt (revision 3)
@@ -1,4 +1,4 @@
Be kind to others
-Freedom = Chocolate Ice Cream
+Freedom = Responsibility
Everything in moderation
Chew with your mouth closed
Not only can you use svn diff to compare files in your working copy to the repository, but if you supply
a URL argument, you can examine the differences between items in the repository without even having
a working copy. This is especially useful if you wish to inspect changes in a file when you don't have a
working copy on your local machine:
Guided Tour
$ svn diff --revision 4:5
svn cat
If you want to examine an earlier version of a file and not necessarily the differences between two files,
you can use svn cat:
$ svn cat --revision 2 rules.txt
Be kind to others
Freedom = Chocolate Ice Cream
Everything in moderation
Chew with your mouth closed
You can also redirect the output directly into a file:
$ svn cat --revision 2 rules.txt > rules.txt.v2
You're probably wondering why we don't just use svn update --revision to update the file to the older
revision. There are a few reasons why we might prefer to use svn cat.
First, you may want to see the differences between two revisions of a file using an external diff program
(perhaps a graphical one, or perhaps your file is in such a format that the output of unified diff is nonsensical). In this case, you'll need to grab a copy of the old revision, redirect it to a file, and pass both
that and the file in your working copy to your external diff program.
Sometimes it's easier to look at an older version of a file in its entirety as opposed to just the differences
between it and another revision.
svn list
The svn list command shows you what files are in a repository directory without actually downloading
the files to your local machine:
$ svn list
If you want a more detailed listing, pass the --verbose (-v) flag to get output like this.
$ svn list --verbose
Guided Tour
1331 Jul
The columns tell you the revision at which the file or directory was last modified, the user who modified
it, the size if it is a file, the date it was last modified, and the item's name.
A Final Word on History
In addition to all of the above commands, you can use svn update and svn checkout with the -revision switch to take an entire working copy “back in time” 6:
$ svn checkout --revision 1729 # Checks out a new working copy at r1729
$ svn update --revision 1729 # Updates an existing working copy to r1729
Other Useful Commands
While not as frequently used as the commands previously discussed in this chapter, you will occasionally need these commands.
svn cleanup
When Subversion modifies your working copy (or any information within .svn), it tries to do so as
safely as possible. Before changing anything, it writes its intentions to a log file, executes the commands
in the log file, then removes the log file (this is similar in design to a journaled filesystem). If a Subversion operation is interrupted (if you hit Control-C, or if the machine crashes, for example), the log files
remain on disk. By re-executing the log files, Subversion can complete the previously started operation,
and your working copy can get itself back into a consistent state.
And this is exactly what svn cleanup does: it searches your working copy and runs any leftover logs, removing locks in the process. If Subversion ever tells you that some part of your working copy is
“locked”, then this is the command that you should run. Also, svn status will display an L next to
locked items:
$ svn status
$ svn cleanup
$ svn status
svn import
The svn import command is a quick way to copy an unversioned tree of files into a repository.
See? We told you that Subversion was a time machine.
Guided Tour
$ svnadmin create /usr/local/svn/newrepos
$ svn import mytree file:///usr/local/svn/newrepos/fooproject
Adding mytree/foo.c
Adding mytree/bar.c
Adding mytree/subdir
Adding mytree/subdir/quux.h
Transmitting file data....
Committed revision 1.
The above example copied the contents of directory mytree under the directory fooproject in the
Now we've covered most of the Subversion client commands. Notable exceptions are those dealing with
branching and merging (see Chapter 4, Branching and Merging) and properties (see the section called
“Properties”). However, you may want to take a moment to skim through Chapter 9, Subversion Complete Reference to get an idea of all the many different commands that Subversion has—and how you
can use them to make your work easier.
Chapter 4. Branching and Merging
Branching, tagging, and merging are concepts common to almost all version control systems. If you're
not familiar with these ideas, we provide a good introduction in this chapter. If you are familiar, then
hopefully you'll find it interesting to see how Subversion implements these ideas.
Branching is a fundamental part of version control. If you're going to allow Subversion to manage your
data, then this is a feature you'll eventually come to depend on. This chapter assumes that you're already
familiar with Subversion's basic concepts (Chapter 2, Basic Concepts).
What's a Branch?
Suppose it's your job to maintain a document for a division in your company, a handbook of some sort.
One day a different division asks you for the same handbook, but with a few parts 'tweaked' for them,
since they do things slightly differently.
What do you do in this situation? You do the obvious thing: you make a second copy of your document,
and begin maintaining the two copies separately. As each department asks you to make small changes,
you incorporate them into one copy or the other.
You often want to make the same change to both copies. For example, if you discover a typo in the first
copy, it's very likely that the same typo exists in the second copy. The two documents are almost the
same, after all; they only differ in small, specific ways.
This is the basic concept of a branch — namely, a line of development that exists independently of another line, yet still shares a common history if you look far enough back in time. A branch always begins
life as a copy of something, and moves on from there, generating its own history.
Figure 4.1. Branches of Development
Subversion has commands to help you maintain parallel branches of your files and directories. It allows
Branching and Merging
you to create branches by copying your data, and remembers that the copies are related to one another. It
also helps you duplicate changes from one branch to another. Finally, it can make portions of your
working copy reflect different branches, so that you can "mix and match" different lines of development
in your daily work.
Using Branches
At this point, you should understand how each commit creates an entire new filesystem tree (called a "revision") in the repository. If not, go back and read about revisions in the section called “Revisions”.
For this chapter, we'll go back to the same example from Chapter 2. Remember that you and your collaborator, Sally, are sharing a repository that contains two projects, paint and calc. Notice, however, that each project directory now contains subdirectories named trunk and branches. The reason
for this will soon become clear.
Figure 4.2. Starting Repository Layout
As before, assume that Sally and you both have working copies of the “calc” project. Specifically, you
each have a working copy of /calc/trunk. All the files for the project are in this subdirectory (rather
than in /calcitself, because your team has decided that /calc/trunk is where the “main line” of
development is going to take place.
Let's say that you've been given the task of performing a radical reorganization of the project. It will take
a long time to write, and will affect all the files in the project. The problem here is that you don't want to
interfere with Sally, who is in the process of fixing small bugs here and there. She's depending on the
fact that the latest version of the project (in /calc/trunk) is always usable. If you start committing
Branching and Merging
your changes bit-by-bit, you'll surely break things for Sally.
One strategy is to crawl into a hole: you and Sally can stop sharing information for a week or two. That
is, start gutting and reorganizing all the files in your working copy, but don't commit or update until
you're completely finished with the task. There are a number of problems with this, though. First, it's not
very safe. Most people like to save their work to the repository frequently, should something bad accidentally happen to their working copy. Second, it's not very flexible. If you do your work on different
computers (perhaps you have a working copy of /calc/trunk on two different machines), you'll
need to manually copy your changes back and forth, or just do all the work on a single computer. By that
same token, it's difficult to share your changes-in-progress with anyone else. A common software development “best practice” to allow your peers to review your work as you go. If nobody sees your intermediate commits, you lose potential feedback. Finally, when you're finished with all your changes, you
might find it very difficult to re-merge your final work with the rest of the company's main body of
code. Sally (or others) may have made many other changes in the repository that are difficult to incorporate into your working copy—especially if you run svn update after weeks of isolation.
The better solution is to create your own branch, or line of development, in the repository. This allows
you to save your half-broken work frequently without interfering with others, yet you can still selectively share information with your collaborators. You'll see exactly how this works later on.
Creating a Branch
Creating a branch is very simple—you make a copy of the project in the repository using the svn copy
command. Subversion is not only able to copy single files, but whole directories as well. In this case,
you want to make a copy of the /calc/trunk directory. Where should the new copy live? Wherever
you wish—it's a matter of project policy. Let's say that your team has a policy of creating branches in
the /calc/branches area of the repository, and you want to name your branch "my-calc-branch".
You'll want to create a new directory, /calc/branches/my-calc-branch, which begins its life
as a copy of /calc/trunk.
There are two different ways to make a copy. We'll demonstrate the messy way first, just to make the
concept clear. To begin, check out a working copy of the project's root directory, /calc:
$ svn checkout bigwc
A bigwc/trunk/
A bigwc/trunk/Makefile
A bigwc/trunk/integer.c
A bigwc/trunk/button.c
A bigwc/branches/
Checked out revision 340.
Making a copy is now simply a matter of passing two working-copy paths to the svn copy command:
$ cd bigwc
$ svn copy trunk/ branches/my-calc-branch
$ svn status
A +
In this case, the svn copy command recursively copies the trunk/ working directory to a new working
directory, branches/my-calc-branch. As you can see from the svn status command, the new directory is now scheduled for addition to the repository. But also notice the “+” sign next to the letter A.
This indicates that the scheduled addition is a copy of something, not something new. When you commit
your changes, Subversion will create /calc/branches/my-calc-branch in the repository by
copying /calc/trunk, rather than resending all of the working copy data over the network:
Branching and Merging
$ svn commit -m "Creating a private branch of /calc/trunk."
Committed revision 341.
And now the easier method of creating a branch, which we should have told you about in the first place:
svn copy is able to operate directly on two URLs.
$ svn copy \ \
-m "Creating a private branch of /calc/trunk."
Committed revision 341.
There's really no difference between these two methods. Both procedures create a new directory in revision 341, and the new directory is a copy of /calc/trunk. Notice that the second method, however,
performs an immediate commit. 7 It's an easier procedure, because it doesn't require you to check out a
large mirror of the repository. In fact, this technique doesn't even require you to have a working copy at
Figure 4.3. Repository With New Copy
Subversion does not support cross-repository copying. When using URLs with svn copy or svn move, you can only copy items
within the same repository.
Branching and Merging
Cheap Copies
Subversion's repository has a special design. When you copy a directory, you don't need to worry about
the repository growing huge—Subversion doesn't actually duplicate any data. Instead, it creates a new
directory entry that points to an existing tree. If you're a Unix user, this is the same concept as a hardlink. From there, the copy is said to be "lazy". That is, if you commit a change to one file within the
copied directory, then only that file changes—the rest of the files continue to exist as links to the original files in the original directory.
This is why you'll often hear Subversion users talk about "cheap copies". It doesn't matter how large the
directory is—it takes a very tiny, constant amount of time to make a copy of it. In fact, this feature is the
basis of how commits work in Subversion: each revision is a "cheap copy" of the previous revision, with
a few items lazily changed within. (To read more about this, visit Subversion's website and read about
the "bubble up" method in Subversion's design documents.)
Of course, these internal mechanics of copying and sharing data are hidden from the user, who simply
sees copies of trees. The main point here is that copies are cheap, both in time and space. Make branches
as often as you want.
Working with Your Branch
Now that you've created a branch of the project, you can check out a new working copy to start using it:
$ svn checkout
A my-calc-branch/Makefile
A my-calc-branch/integer.c
A my-calc-branch/button.c
Checked out revision 341.
There's nothing special about this working copy; it simply mirrors a different directory in the repository.
When you commit changes, however, Sally won't ever see them when she updates. Her working copy is
of /calc/trunk. (Be sure to read the section called “Switching a Working Copy” later in this chapter: the svn switch command is an alternate way of creating a working copy of a branch.)
Let's pretend that a week goes by, and the following commits happen:
You make a change to /calc/branches/my-calc-branch/button.c, which creates revision 342.
You make a change to /calc/branches/my-calc-branch/integer.c, which creates revision 343.
Sally makes a change to /calc/trunk/integer.c, which creates revision 344.
There are now two independent lines of development happening on integer.c:
Figure 4.4. The Branching of One File's History
Branching and Merging
Things get interesting when you look at the history of changes made to your copy of integer.c:
$ pwd
$ svn log --verbose integer.c
-----------------------------------------------------------------------r343 | user | 2002-11-07 15:27:56 -0600 (Thu, 07 Nov 2002) | 2 lines
Changed paths:
M /calc/branches/my-calc-branch/integer.c
* integer.c:
frozzled the wazjub.
-----------------------------------------------------------------------r341 | user | 2002-11-03 15:27:56 -0600 (Thu, 07 Nov 2002) | 2 lines
Changed paths:
A /calc/branches/my-calc-branch (from /calc/trunk:340)
Creating a private branch of /calc/trunk.
-----------------------------------------------------------------------r303 | sally | 2002-10-29 21:14:35 -0600 (Tue, 29 Oct 2002) | 2 lines
Changed paths:
M /calc/trunk/integer.c
* integer.c:
changed a docstring.
-----------------------------------------------------------------------r98 | sally | 2002-02-22 15:35:29 -0600 (Fri, 22 Feb 2002) | 2 lines
Changed paths:
Branching and Merging
M /calc/trunk/integer.c
* integer.c:
adding this file to the project.
-----------------------------------------------------------------------Notice that Subversion is tracing the history of your branch's integer.c all the way back through
time, even traversing the point where it was copied. It shows the creation of the branch as an event in the
history, because integer.c was implicitly copied when all of /calc/trunk/ was copied. Now
look what happens when Sally runs the same command on her copy of the file:
$ pwd
$ svn log --verbose integer.c
-----------------------------------------------------------------------r344 | sally | 2002-11-07 15:27:56 -0600 (Thu, 07 Nov 2002) | 2 lines
Changed paths:
M /calc/trunk/integer.c
* integer.c:
fix a bunch of spelling errors.
-----------------------------------------------------------------------r303 | sally | 2002-10-29 21:14:35 -0600 (Tue, 29 Oct 2002) | 2 lines
Changed paths:
M /calc/trunk/integer.c
* integer.c:
changed a docstring.
-----------------------------------------------------------------------r98 | sally | 2002-02-22 15:35:29 -0600 (Fri, 22 Feb 2002) | 2 lines
Changed paths:
M /calc/trunk/integer.c
* integer.c:
adding this file to the project.
-----------------------------------------------------------------------Sally sees her own revision 344 change, but not the change you made in revision 343. As far as Subversion is concerned, these two commits affected different files in different repository locations. However,
Subversion does show that the two files share a common history. Before the branch-copy was made in
revision 341, they used to be the same file. That's why you and Sally both see the changes made in revisions 303 and 98.
The Moral of the Story
There are two important lessons that you should remember from this section.
Unlike many other version control systems, Subversion's branches exist as normal filesystem directories in the repository, not in an extra dimension. These directories just happen to carry some extra
historical information.
Subversion has no internal concept of a branch — only copies. When you copy a directory, the resulting directory is only a "branch" because you attach that meaning to it. You may think of the directory differently, or treat it differently, but to Subversion it's just an ordinary directory that happens to have been created by copying.
Branching and Merging
Copying Changes Between Branches
Now you and Sally are working on parallel branches of the project: you're working on a private branch,
and Sally is working on the trunk, or main line of development.
For projects that have a large number of contributors, it's common for most people to have working
copies of the trunk. Whenever someone needs to make a long-running change that is likely to disrupt the
trunk, a standard procedure is to create a private branch and commit changes there until all the work is
So, the good news is that you and Sally aren't interfering with each other. The bad news is that it's very
easy to drift too far apart. Remember that one of the problems with the "crawl in a hole" strategy is that
by the time you're finished with your branch, it may be near-impossible to merge your changes back into
the trunk without a huge number of conflicts.
Instead, you and Sally might continue to share changes as you work. It's up to you to decide which
changes are worth sharing; Subversion gives you the ability to selectively "copy" changes between
branches. And when you're completely finished with your branch, your entire set of branch changes can
be copied back into the trunk.
Copying Specific Changes
In the previous section, we mentioned that both you and Sally made changes to integer.c on different branches. If you look at Sally's log message for revision 344, you can see that she fixed some
spelling errors. No doubt, your copy of the same file still has the same spelling errors. It's likely that
your future changes to this file will be affecting the same areas that have the spelling errors, so you're in
for some potential conflicts when you merge your branch someday. It's better, then, to receive Sally's
change now, before you start working too heavily in the same places.
It's time to use the svn merge command. This command, it turns out, is a very close cousin to the svn
diff command (which you read about in Chapter 3). Both commands are able to compare any two objects in the repository and describe the differences. For example, you can ask svn diff to show you the
exact change made by Sally in revision 344:
$ svn diff -r 343:344
Index: integer.c
--- integer.c (revision 343)
+++ integer.c (revision 344)
@@ -147,7 +147,7 @@
case 6: sprintf(info->operating_system, "HPFS (OS/2 or NT)"); break;
case 7: sprintf(info->operating_system, "Macintosh"); break;
case 8: sprintf(info->operating_system, "Z-System"); break;
case 9: sprintf(info->operating_system, "CPM"); break;
case 9: sprintf(info->operating_system, "CP/M"); break;
case 10: sprintf(info->operating_system, "TOPS-20"); break;
case 11: sprintf(info->operating_system, "NTFS (Windows NT)"); break;
case 12: sprintf(info->operating_system, "QDOS"); break;
@@ -164,7 +164,7 @@
low = (unsigned short) read_byte(gzfile); /* read LSB */
high = (unsigned short) read_byte(gzfile); /* read MSB */
high = high << 8; /* interpret MSB correctly */
total = low + high; /* add them togethe for correct total */
total = low + high; /* add them together for correct total */
info->extra_header = (unsigned char *) my_malloc(total);
fread(info->extra_header, total, 1, gzfile);
@@ -241,7 +241,7 @@
Branching and Merging
Store the offset with ftell() ! */
if ((info->data_offset = ftell(gzfile))== -1) {
printf("error: ftell() retturned -1.\n");
printf("error: ftell() returned -1.\n");
@@ -249,7 +249,7 @@
printf("I believe start of compressed data is %u\n", info->data_offset);
/* Set postion eight bytes from the end of the file. */
/* Set position eight bytes from the end of the file. */
if (fseek(gzfile, -8, SEEK_END)) {
printf("error: fseek() returned non-zero\n");
The svn merge is almost exactly the same. Instead of printing the differences to your terminal, however,
it applies them directly to your working copy as local modifications:
$ svn merge -r 343:344
U integer.c
$ svn status
M integer.c
The output of svn merge shows that your copy of integer.c was patched. It now contains Sally's
change — it has been "copied" from the trunk to your working copy of your private branch, and now exists as a local modification. At this point, it's up to you to review the local modification and make sure it
works correctly.
In another scenario, it's possible that things may not have gone so well, and that integer.c may have
entered a conflicted state. You might need to resolve the conflict using standard procedures (see Chapter
3), or if you decide that the merge was a bad idea altogether, simply give up and svn revert the local
But assuming that you've reviewed the merged change, you can svn commit the change as usual. At that
point, the change has been merged into your repository branch. In version control terminology, this act
of copying changes between branches is commonly called porting changes.
When you commit the local modification, make sure your log message mentions that you're porting a
specific change from one branch to another. For example:
$ svn commit -m "integer.c: ported r344 (spelling fixes) from trunk."
Transmitting file data .
Committed revision 360.
As you'll see in the next sections, this is a very important "best practice" to follow.
Why Not Use Patches Instead?
A question may be on your mind, especially if you're a Unix user: why bother to use svn merge at all?
Why not simply use the operating system's patch command to accomplish the same job? For example:
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$ svn diff -r 343:344 > patchfile
$ patch -p0 < patchfile
Patching file integer.c using Plan A...
Hunk #1 succeeded at 147.
Hunk #2 succeeded at 164.
Hunk #3 succeeded at 241.
Hunk #4 succeeded at 249.
In this particular case, yes, there really is no difference. But svn merge has special abilities that surpass
the patch program. The file format used by patch is quite limited; it's only able to tweak file contents.
There's no way to represent changes to trees, such as the addition, removal, or renaming of files and directories. If Sally's change had, say, added a new directory, the output of svn diff wouldn't have mentioned it at all. svn diff only outputs the limited patch-format, so there are some ideas it simply can't express. 8 The svn merge command, however, can express tree-changes by directly applying them to your
working copy.
A word of warning: while svn diff and svn merge are very similar in concept, they do have different
syntax in many cases. Be sure to read about them in Chapter 8 for details, or ask svn help. For example,
svn merge requires a working-copy path as a target, i.e. a place where it should apply the tree-changes.
If the target isn't specified, it assumes you are trying to perform one of the following common operations:
You want to merge directory changes into your current working directory.
You want to merge the changes in a specific file into a file by the same name which exists in your
current working directory.
If you are merging a directory and haven't specified a target path, svn merge assumes the first case
above and tries to apply the changes into your current directory. If you are merging a file, and that file
(or a file by the same name) exists in your current working directory, svn merge assumes the second
case and tries to apply the changes to a local file with the same name.
If you want changes applied somewhere else, you'll need to say so. For example, if you're sitting in the
parent directory of your working copy, you'll have to specify the target directory to receive the changes:
$ svn merge -r 343:344 my-calc-branch
Best Practices for Merging
Tracking Merges Manually
Merging changes sounds simple enough, but in practice it can become a headache. The problem is that if
you repeatedly merge changes from one branch to another, you might accidentally merge the same
change twice. When this happens, sometimes things will work fine. When patching a file, Subversion
typically notices if the file already has the change, and does nothing. But if the already-existing change
has been modified in any way, you'll get a conflict.
Ideally, your version control system should prevent the double-application of changes to a branch. It
In the future, the Subversion project plans to use (or invent) an expanded patch format that describes tree-changes.
Branching and Merging
should automatically remember which changes a branch has already received, and be able to list them
for you. It should use this information to help automate merges as much as possible.
Unfortunately, Subversion is not such a system. Like CVS, Subversion 1.0 does not yet record any information about merge operations. When you commit local modifications, the repository has no idea
whether those changes came from running svn merge, or from just hand-editing the files.
What does this mean to you, the user? It means that until the day Subversion grows this feature, you'll
have to track merge information yourself. The best place to do this is in the commit log-message. As
demonstrated in the earlier example, it's recommended that your log-message mention a specific revision number (or range of revisions) that are being merged into your branch. Later on, you can run svn
log to review which changes your branch already contains. This will allow you to carefully construct a
subsequent svn merge command that won't be redundant with previously ported changes.
In the next section, we'll show some examples of this technique in action.
Previewing Merges
Because merging only results in local modifications, it's not usually a high-risk operation. If you get the
merge wrong the first time, simply svn revert the changes and try again.
It's possible, however, that your working copy might already have local modifications. The changes applied by a merge will be mixed with your pre-existing ones, and running svn revert is no longer an option. The two sets of changes may be impossible to separate.
In cases like this, people take comfort in being able to predict or examine merges before they happen.
One simple way to do that is to run svn diff with the same arguments you plan to pass to svn merge, as
we already showed in our first example of merging. Another method of previewing is to pass the -dry-run option to the merge command:
$ svn merge --dry-run -r 343:344
U integer.c
$ svn status
# nothing printed, working copy is still unchanged.
The --dry-run option doesn't actually apply any local changes to the working copy. It only shows
status codes that would be printed in a real merge. It's useful for getting a "high level" preview of the potential merge, for those times when running svn diff gives too much detail.
Subversion and Changesets
Everyone seems to have a slightly different definition of “changeset”, or a least a different expectation
of what it means for a version control system to have “changeset features”. For our purpose, let's say
that a changeset is just a collection of changes with a unique name. The changes might include textual
edits to file contents, modifications to tree structure, or tweaks to metadata. In more common speak, a
changeset is just a patch with a name you can refer to.
In Subversion, a global revision number N names a tree in the repository: it's the way the repository
looked after the Nth commit. It's also the name of an implicit changeset: if you compare tree N with tree
N-1, you can derive the exact patch that was committed. For this reason, it's easy to think of “revision
N” as not just a tree, but a changeset as well. If you use an issue tracker to manage bugs, you can use the
revision numbers to refer to particular patches that fix bugs—for example, “this issue was fixed by revision 9238.”. Somebody can then run svn log -r9238 to read about the exact changeset which fixed the
bug, and run svn diff -r9237:9238 to see the patch itself. And Subversion's merge command also uses
revision numbers. You can merge specific changesets from one branch to another by naming them in the
Branching and Merging
merge arguments: svn merge -r9237:9238 would merge changeset #9238 into your working copy.
Common Use-Cases for Merging
There are many different uses for svn merge, and this section describes the most common ones you're
likely to run into.
Merging a Whole Branch to Another
To complete our running example, we'll move forward in time. Suppose several days have passed, and
many changes have happened on both the trunk and your private branch. Suppose that you've finished
working on your private branch; the feature or bugfix is finally complete, and now you want to merge all
of your branch changes back into the trunk for others to enjoy.
So how do we use svn merge in this scenario? Remember that this command compares two trees, and
applies the differences to a working copy. So to receive the changes, you need to have a working copy
of the trunk. We'll assume that either you still have your original one lying around (fully updated), or
that you recently checked out a fresh working copy of /calc/trunk.
But which two trees should be compared? At first glance, the answer may seem obvious: just compare
the latest trunk tree with your latest branch tree. But beware — this assumption is wrong, and has burned
many a new user! Since svn merge operates like svn diff, comparing the latest trunk and branch trees
will not merely describe the set of changes you made to your branch. Such a comparison shows too
many changes: it would not only show the addition of your branch changes, but also the removal of
trunk changes that never happened on your branch.
To express only the changes that happened on your branch, you need to compare the initial state of your
branch to its final state. Using svn log on your branch, you can see that your branch was created in revision 341. And the final state of your branch is simply a matter of using the HEAD revision. That means
you want to compare revisions 341 and HEAD of your branch directory, and apply those differences to a
working copy of the trunk.
Here's the final merging procedure, then:
$ cd calc/trunk
$ svn up
At revision 405.
$ svn merge -r 341:HEAD
$ svn status
# ...examine the diffs, compile, test, etc...
$ svn commit -m "Merged my-calc-branch changes r341:405 into the trunk."
Transmitting file data ...
Committed revision 406.
Branching and Merging
Again, notice that the commit log message very specifically mentions the range of changes that was
merged into the trunk. Always remember to do this, because it's critical information you'll need later on.
For example, suppose you decide to keep working on your branch for another week, in order to complete an enhancement to your original feature or bugfix. The repository's HEAD revision is now 480,
and you're ready to do another merge from your private branch to the trunk. But as discussed in the section called “Best Practices for Merging”, you don't want to merge the changes you've already merged
before; you only want to merge everything “new” on your branch since the last time you merged. The
trick is to figure out what's new.
The first step is to run svn log on the trunk, and look for a log message about the last time you merged
from the branch:
$ cd calc/trunk
$ svn log
-----------------------------------------------------------------------r406 | user | 2004-02-08 11:17:26 -0600 (Sun, 08 Feb 2004) | 1 line
Merged my-calc-branch changes r341:405 into the trunk.
Aha! Since all branch-changes that happened between revisions 341 and 405 were previously merged to
the trunk, you now know that you want to merge only the branch changes after that: revisions 406
through HEAD.
$ cd calc/trunk
$ svn up
At revision 480.
$ svn merge -r 406:480
$ svn commit -m "Merged my-calc-branch changes r406:480 into the trunk."
Transmitting file data ...
Committed revision 481.
Now the trunk contains the complete second wave of changes made to the branch. At this point, you can
either delete your branch (we'll discuss this later on), or continue working on your branch and repeat this
procedure for subsequent merges.
Undoing Changes
Another common use for svn merge is to roll back a change that has already been committed. Suppose
you working away happily on a working copy of /calc/trunk, and you discover that the change
made way back in revision 303, which changed integer.c, is completely wrong. It never should have
been committed. You can use svn merge to "undo" the change in your working copy, and then commit
the local modification to the repository. All you need to do is to specify a reverse difference:
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$ svn merge -r 303:302
U integer.c
$ svn status
M integer.c
$ svn diff
# verify that the change is removed
$ svn commit -m "Undoing change committed in r303."
Transmitting file data .
Committed revision 350.
One way to think about a repository revision is as a specific group of changes (some version control systems call these changesets). By using the -r switch, you can ask svn merge to apply a changeset, or
whole range of changesets, to your working copy. In our case of undoing a change, we're asking svn
merge to apply changeset #303 to our working copy backwards.
Keep in mind that rolling back a change like this is just like any other svn merge operation, so you
should use svn status and svn diff to confirm that your work is in the state you want it to be in, and then
use svn commit to send the final version to the repository. After committing, this particular changeset is
no longer reflected in the HEAD revision.
Again, you may be thinking: well, that really didn't undo the commit, did it? The change still exists in
revision 303. If somebody checks out a version of the calc project between revisions 303 and 349,
they'll still see the bad change, right?
Yes, that's true. When we talk about "removing" a change, we're really talking about "removing it from
HEAD". The original change still exists in the repository's history. For most situations, this is good
enough. Most people are only interested in tracking the HEAD of a project anyway. There are special
cases, however, where you really might want to destroy all evidence of the commit. (Perhaps somebody
accidentally committed a confidential document.) This isn't so easy, it turns out, because Subversion was
deliberately designed to never lose information. Revisions are immutable trees which build upon one another. Removing a revision from history would cause a domino effect, creating chaos in all subsequent
revisions and possibly invalidating all working copies. 9
Resurrecting Deleted Items
The great thing about version control systems is that information is never lost. Even when you delete a
file or directory, it may be gone from the HEAD revision, but the object still exists in earlier revisions.
One of the most common FAQs from new users is: "how do I get my old file or directory back?"
The first step is to define exactly which item you're trying to resurrect. Here's a useful metaphor: you
can think of every object in the repository as existing in a sort of two-dimensional coordinate system.
The first coordinate is a particular revision tree, and the second coordinate is a path within that tree. So
every version of your file or directory can be defined by a specific coordinate pair.
Subversion has no "attic" directory like CVS does 10, so you need to use svn log to discover the exact
coordinate pair you wish to resurrect. A good strategy is to run svn log --verbose in a directory which
used to contain your deleted item. The --verbose option shows a list of all changed items in each revision; all you need to do is find the revision in which you deleted the file or directory. You can do this
visually, or by using another tool to examine the log output (via grep, or perhaps via an incremental
search in an editor.)
The Subversion project has plans, however, to someday implement an svnadmin obliterate command that would accomplish the
task of permanently deleting information. In the meantime, see the section called “svndumpfilter” for a possible workaround.
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$ cd parent-dir
$ svn log --verbose
-----------------------------------------------------------------------r808 | joe | 2003-12-26 14:29:40 -0600 (Fri, 26 Dec 2003) | 3 lines
Changed paths:
D /calc/trunk/real.c
M /calc/trunk/integer.c
In the example, we're assuming that you're looking for a deleted file real.c. By looking through the
logs of a parent directory, you've spotted that this file was deleted in revision 808. Therefore, the last
version of the file to exist was in the revision right before that. Conclusion: you want to resurrect the
path /calc/trunk/real.c from revision 807.
That was the hard part — the research. Now that you know what you want to restore, you have two different choices.
One option is to use svn merge to apply revision 808 "in reverse". (We've already discussed how to
undo changes, see the section called “Undoing Changes”.) This would have the affect of re-adding
real.c as a local modification. The file would be scheduled for addition, and after a commit, the file
would again exist in HEAD.
In this particular example, however, this is probably not the best strategy. Reverse-applying revision 808
would not only schedule real.c for addition, but the log message indicates that it would also undo
certain changes to integer.c, which you don't want. Certainly, you could reverse-merge revision 808
and then svn revert the local modifications to integer.c, but this technique doesn't scale well. What
if there were 90 files changed in revision 808?
A second, more targeted strategy is not to use svn merge at all, but rather the svn copy command. Simply copy the exact revision and path "coordinate pair" from the repository to your working copy:
$ svn copy --revision 807 \ ./real.c
$ svn status
A +
$ svn commit -m "Resurrected real.c from revision 807, /calc/trunk/real.c."
Transmitting file data .
Committed revision 1390.
The plus sign in the status output indicates that the item isn't merely scheduled for addition, but scheduled for addition “with history.” Subversion remembers where it was copied from. In the future, running
svn log on this file will traverse back through the file's resurrection and through all the history it had
prior to revision 807. In other words, this new real.c isn't really new; it's a direct descendant of the
original, deleted file.
Although our example shows us resurrecting a file, note that these same techniques work just as well for
resurrecting deleted directories.
Switching a Working Copy
The svn switch command transforms an existing working copy into a different branch. While this com53
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mand isn't strictly necessary for working with branches, it provides a nice shortcut to users. In our earlier
example, after creating your private branch, you checked out a fresh working copy of the new repository
directory. Instead, you can simply ask Subversion to change your working copy of /calc/trunk to
mirror the new branch location:
$ cd calc
$ svn info | grep URL
$ svn switch
Updated to revision 341.
$ svn info | grep URL
After "switching" to the branch, your working copy is no different than what you would get from doing
a fresh checkout of the directory. And it's usually more efficient to use this command, because often
branches only differ by a small degree. The server sends only the minimal set of changes necessary to
make your working copy reflect the branch directory.
The svn switch command also takes a --revision (-r) option, so you need not always move your
working copy to the “tip” of the branch.
Of course, most projects are more complicated than our calc example, containing multiple subdirectories. Subversion users often follow a specific algorithm when using branches:
Copy the project's entire 'trunk' to a new branch directory.
Switch only part of the trunk working copy to mirror the branch.
In other words, if a user knows that the branch-work only needs to happen on a specific subdirectory,
they use svn switch to move only that subdirectory to the branch. (Or sometimes users will switch just a
single working file to the branch!) That way, they can continue to receive normal 'trunk' updates to most
of their working copy, but the switched portions will remain immune (unless someone commits a change
to their branch). This feature adds a whole new dimension to the concept of a "mixed working copy" —
not only can working copies contain a mixture of working revisions, but a mixture of repository locations as well.
If your working copy contains a number of switched subtrees from different repository locations, it continues to function as normal. When you update, you'll receive patches to each subtree as appropriate.
When you commit, your local changes will still be applied as a single, atomic change to the repository.
Note that while it's okay for your working copy to reflect a mixture of repository locations, these locations must all be within the same repository. Subversion repositories aren't yet able to communicate with
one another; that's a feature planned beyond Subversion 1.0.11
Switches and Updates
Have you noticed that the output of svn switch and svn update look the same? The switch command is
You can, however, use svn switch with the --relocate switch if the URL of your server changes and you don't want to
abandon an existing working copy. See the svn switch section in Chapter 9, Subversion Complete Reference for more information
and an example.
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actually a superset of the update command.
When you run svn update, you're asking the repository to compare two trees. The repository does so,
and then sends a description of the differences back to the client. The only difference between svn
switch and svn update is that the update command always compares two identical paths.
That is, if your working copy is a mirror of /calc/trunk, then svn update will automatically compare your working copy of /calc/trunk to /calc/trunk in the HEAD revision. If you're switching your working copy to a branch, then svn switch will compare your working copy of /
calc/trunk to some other branch-directory in the HEAD revision.
In other words, an update moves your working copy through time. A switch moves your working copy
through time and space.
Because svn switch is essentially a variant of svn update, it shares the same behaviors; any local modifications in your working copy are preserved when new data arrives from the repository. This allows
you to perform all sorts of clever tricks.
For example, suppose you have a working copy of /calc/trunk and make a number of changes to it.
Then you suddenly realize that you meant to make the changes to a branch instead. No problem! When
you svn switch your working copy to the branch, the local changes will remain. You can then test and
commit them to the branch.
Another common version control concept is a tag. A tag is just a “snapshot” of a project in time. In Subversion, this idea already seems to be everywhere. Each repository revision is exactly that — a snapshot
of the filesystem after each commit.
However, people often want to give more human-friendly names to tags, like "release-1.0". And they
want to make snapshots of smaller subdirectories of the filesystem. After all, it's not so easy to remember that release-1.0 of a piece of software is a particular subdirectory of revision 4822.
Creating a Simple Tag
Once again, svn copy comes to the rescue. If you want to create a snapshot of /calc/trunk exactly
as it looks in the HEAD revision, then make a copy of it:
$ svn copy \ \
-m "Tagging the 1.0 release of the 'calc' project."
Committed revision 351.
This example assumes that a /calc/tags directory already exists. After the copy completes, the new
release-1.0 directory is forever a snapshot of how the project looked in the HEAD revision at the
time you made the copy. Of course you might want to be more precise about exactly which revision you
copy, in case somebody else may have committed changes to the project when you weren't looking. So
if you know that revision 350 of /calc/trunk is exactly the snapshot you want, you can specify it by
passing -r 350 to the svn copy command.
But wait a moment: isn't this tag-creation procedure the same procedure we used to create a branch?
Yes, in fact, it is. In Subversion, there's no difference between a tag and a branch. Both are just ordinary
directories that are created by copying. Just as with branches, the only reason a copied directory is a
Branching and Merging
” is because humans have decided to treat it that way: as long as nobody ever commits to the directory, it
forever remains a snapshot. If people start committing to it, it becomes a branch.
If you are administering a repository, there are two approaches you can take to managing tags. The first
approach is “hands off”: as a matter of project policy, decide where your tags will live, and make sure
all users know how to treat the directories they copy in there. (That is, make sure they know not to commit to them.) The second approach is more paranoid: you can use one of the access-control scripts provided with Subversion to prevent anyone from doing anything but creating new copies in the tags-area
(See Chapter 6, Server Configuration.) The paranoid approach, however, isn't usually necessary. If a
user accidentally commits a change to a tag-directory, you can simply undo the change as discussed in
the previous section. This is version control, after all.
Creating a Complex Tag
Sometimes you may want your "snapshot" to be more complicated than a single directory at a single revision.
For example, pretend your project is much larger than our calc example: suppose it contains a number
of subdirectories and many more files. In the course of your work, you may decide that you need to create a working copy that is designed to have specific features and bugfixes. You can accomplish this by
selectively backdating files or directories to particular revisions (using svn update -r liberally), or by
switching files and directories to particular branches (making use of svn switch). When you're done,
your working copy is a hodgepodge of repository locations from different revisions. But after testing,
you know it's the precise combination of data you need.
Time to make a snapshot. Copying one URL to another won't work here. In this case, you want to make
a snapshot of your exact working copy arrangement and store it in the repository. Luckily, svn copy actually has four different uses (which you can read about in Chapter 9), including the ability to copy a
working-copy tree to the repository:
$ ls
$ svn copy my-working-copy
Committed revision 352.
Now there is a new directory in the repository, /calc/tags/mytag, which is an exact snapshot of
your working copy — mixed revisions, urls, and all.
Other users have found interesting uses for this feature. Sometimes there are situations where you have a
bunch of local changes made to your working copy, and you'd like a collaborator to see them. Instead of
running svn diff and sending a patchfile (which won't capture tree changes), you can instead use svn
copy to "upload" your working copy to a private area of the repository. Your collaborator can then either
checkout a verbatim copy of your working copy, or use svn merge to receive your exact changes.
Branch Maintenance
You may have noticed by now that Subversion is extremely flexible. Because it implements branches
and tags with the same underlying mechanism (directory copies), and because branches and tags appear
in normal filesystem space, many people find Subversion intimidating. It's almost too flexible. In this
section, we'll offer some suggestions for arranging and managing your data over time.
Repository Layout
There are some standard, recommended ways to organize a repository. Most people create a trunk di56
Branching and Merging
rectory to hold the “main line” of development, a branches directory to contain branch copies, and a
tags directory to contain tag copies. If a repository holds only one project, then often people create
these top-level directories:
If a repository contains multiple projects, admins typically index their layout by project (see the section
called “Choosing a Repository Layout” to read more about "project roots"):
Of course, you're free to ignore these common layouts. You can create any sort of variation, whatever
works best for you or your team. Remember that whatever you choose, it's not a permanent commitment. You can reorganize your repository at any time. Because branches and tags are ordinary directories, the svn move command can move or rename them however you wish. Switching from one layout
to another is just a matter of issuing a series of server-side moves; if you don't like the way things are organized in the repository, just juggle the directories around.
Remember, though, that while moving directories may be easy to do, you need to be considerate of your
users as well. Your juggling can be disorienting to users with existing working copies. If a user has a
working copy of a particular repository directory, your svn move operation might remove the path from
the latest revision. When the user next runs svn update, they'll be told that their working copy represents a path that no longer exists, and the user will be forced to svn switch to the new location.
Data Lifetimes
Another nice feature of Subversion's model is that branches and tags can have finite lifetimes, just like
any other versioned item. For example, suppose you eventually finish all your work on your personal
branch of the calc project. After merging all of your changes back into /calc/trunk, there's no
need for your private branch directory to stick around anymore:
$ svn delete \
-m "Removing obsolete branch of calc project."
Committed revision 375.
And now your branch is gone. Of course it's not really gone: the directory is simply missing from the
HEAD revision, no longer distracting anyone. If you look at an earlier revision (by means of svn checkout -r, svn switch -r, or svn list -r), you'll still be able to see your old branch.
If browsing your deleted directory isn't enough, you can always bring it back. Resurrecting data is very
easy in Subversion. If there's a deleted directory (or file) that you'd like to bring back into HEAD, simply use svn copy -r to copy it from the old revision:
$ svn copy -r 374 \
Branching and Merging
Committed revision 376.
In our example, your personal branch had a relatively short lifetime: you may have created it to fix a bug
or implement a new feature. When your task is done, so is the branch. In software development, though,
it's also common to have two "main" branches running side-by-side for very long periods. For example,
suppose it's time to release a stable calc project to the public, and you know it's going to take a couple
of months to shake bugs out of the software. You don't want people to add new features to the project,
but you don't want to tell all developers to stop programming either. So instead, you create a "stable"
branch of the software that won't change much:
$ svn copy \ \
-m "Creating stable branch of calc project."
Committed revision 377.
And now developers are free to continue adding cutting-edge (or experimental) features to /
calc/trunk, and you can declare a project policy that only bugfixes are to be committed to /
calc/branches/stable-1.0. That is, as people continue to work on the trunk, a human selectively ports bugfixes over to the stable branch. Even after the stable branch has shipped, you'll probably
continue to maintain the branch for a long time — that is, as long as you continue to support that release
for customers.
We've covered a lot of ground in this chapter. We've discussed the concepts of tags and branches, and
demonstrated how Subversion implements these concepts by copying directories with the svn copy
command. We've shown how to use svn merge to copy changes from one branch to another, or roll back
bad changes. We've gone over the use of svn switch to create mixed-location working copies. And
we've talked about how one might manage the organization and lifetimes of branches in a repository.
Remember the Subversion mantra: branches and tags are cheap. So use them liberally!
Chapter 5. Repository Administration
The Subversion repository is the central storehouse of versioned data for any number of projects. As
such, it becomes an obvious candidate for all the love and attention an administrator can offer. While the
repository is generally a low-maintenance item, it is important to understand how to properly configure
and care for it so that potential problems are avoided, and actual problems are safely resolved.
In this chapter, we'll discuss how to create and configure a Subversion repository, and how to expose
that repository for network accessibility. We'll also talk about repository maintenance, including the use
of the svnlook and svnadmin tools (which are provided with Subversion). We'll address some common
questions and mistakes, and give some suggestions on how to arrange the data in the repository.
If you plan to access a Subversion repository only in the role of a user whose data is under version control (that is, via a Subversion client), you can skip this chapter altogether. However, if you are, or wish
to become, a Subversion repository administrator, 12 you should definitely pay attention to this chapter.
Repository Basics
Understanding Transactions and Revisions
Conceptually speaking, a Subversion repository is a sequence of directory trees. Each tree is a snapshot
of how the files and directories versioned in your repository looked at some point in time. These snapshots are created as a result of client operations, and are called revisions.
Every revision begins life as a transaction tree. When doing a commit, a client builds a Subversion transaction that mirrors their local changes (plus any additional changes that might have been made to the
repository since the beginning of the client's commit process), and then instructs the repository to store
that tree as the next snapshot in the sequence. If the commit succeeds, the transaction is effectively promoted into a new revision tree, and is assigned a new revision number. If the commit fails for some reason, the transaction is destroyed and the client is informed of the failure.
Updates work in a similar way. The client builds a temporary transaction tree that mirrors the state of the
working copy. The repository then compares that transaction tree with the revision tree at the requested
revision (usually the most recent, or “youngest” tree), and sends back information that informs the client
about what changes are needed to transform their working copy into a replica of that revision tree. After
the update completes, the temporary transaction is deleted.
The use of transaction trees is the only way to make permanent changes to a repository's versioned
filesystem. However, it's important to understand that the lifetime of a transaction is completely flexible.
In the case of updates, transactions are temporary trees that are immediately destroyed. In the case of
commits, transactions are transformed into permanent revisions (or removed if the commit fails). In the
case of an error or bug, it's possible that a transaction can be accidentally left lying around in the repository (not really affecting anything, but still taking up space).
In theory, someday whole workflow applications might revolve around more fine-grained control of
transaction lifetime. It is feasible to imagine a system whereby each transaction slated to become a revision is left in stasis well after the client finishes describing its changes to repository. This would enable
each new commit to be reviewed by someone else, perhaps a manager or engineering QA team, who can
choose to promote the transaction into a revision, or abort it.
Unversioned Properties
This may sound really prestigious and lofty, but we're just talking about anyone who is interested in that mysterious realm beyond the working copy where everyone's data hangs out.
Repository Administration
Transactions and revisions in the Subversion repository can have properties attached to them. These
properties are generic key-to-value mappings, and are generally used to store information about the tree
to which they are attached. The names and values of these properties are stored in the repository's
filesystem, along with the rest of your tree data.
Revision and transaction properties are useful for associating information with a tree that is not strictly
related to the files and directories in that tree—the kind of information that isn't managed by client
working copies. For example, when a new commit transaction is created in the repository, Subversion
adds a property to that transaction named svn:date—a datestamp representing the time that the transaction was created. By the time the commit process is finished, and the transaction is promoted to a permanent revision, the tree has also been given a property to store the username of the revision's author
(svn:author) and a property to store the log message attached to that revision (svn:log).
Revision and transaction properties are unversioned properties—as they are modified, their previous
values are permanently discarded. Also, while revision trees themselves are immutable, the properties
attached to those trees are not. You can add, remove, and modify revision properties at any time in the
future. If you commit a new revision and later realize that you had some misinformation or spelling error
in your log message, you can simply replace the value of the svn:log property with a new, corrected
log message.
Berkeley DB
The data housed within Subversion repositories actually lives inside a database, specifically, a Berkeley
DB Data Store. When the initial design phase of Subversion was in progress, the developers decided to
use Berkeley DB for a variety of reasons, including its open-source license, transaction support, reliability, performance, API simplicity, thread-safety, support for cursors, and so on.
Berkeley DB provides real transaction support— perhaps its most powerful feature. Multiple processes
accessing your Subversion repositories don't have to worry about accidentally clobbering each other's
data. The isolation provided by the transaction system is such that for any given operation, the Subversion repository code sees a static view of the database—not a database that is constantly changing at the
hand of some other process—and can make decisions based on that view. If the decision made happens
to conflict with what another process is doing, the entire operation is rolled back as if it never happened,
and Subversion gracefully retries the operation against a new, updated (and yet still static) view of the
Another great feature of Berkeley DB is hot backups—the ability to backup the database environment
without taking it “offline”. We'll discuss how to backup your repository in the section called Reposi“tory Backup”, but the benefits of being able to make fully functional copies of your repositories without any downtime should be obvious.
Berkeley DB is also a very reliable database system. Subversion uses Berkeley DB's logging facilities,
which means that the database first writes to on-disk logfiles a description of any modifications it is
about to make, and then makes the modification itself. This is to ensure that if anything goes wrong, the
database system can back up to a previous checkpoint—a location in the logfiles known not to be corrupt—and replay transactions until the data is restored to a usable state. See the section called Manag“ing Disk Space” for more about Berkeley DB logfiles.
But every rose has its thorn, and so we must note some known limitations of Berkeley DB. First, Berkeley DB environments are not portable. You cannot simply copy a Subversion repository that was created
on a Unix system onto a Windows system and expect it to work. While much of the Berkeley DB
database format is architecture independent, there are other aspects of the environment that are not. Secondly, Subversion uses Berkeley DB in a way that will not operate on Windows 95/98 systems—if you
need to house a repository on a Windows machine, stick with Windows 2000 or Windows XP. Finally,
you should never keep a Subversion repository on a network share. While Berkeley DB promises to behave correctly on network shares that meet a particular set of specifications, almost no known shares actually meet all those specifications.
Repository Administration
Repository Creation and Configuration
Creating a Subversion repository is an incredibly simple task. The svnadmin utility, provided with Subversion, has a subcommand for doing just that. To create a new repository, just run:
$ svnadmin create path/to/repos
This creates a new repository in the directory path/to/repos. This new repository begins life at revision 0, which is defined to consist of nothing but the top-level root (/) filesystem directory. Initially,
revision 0 also has a single revision property, svn:date, set to the time at which the repository was
Do not create your repository on a network share—it cannot exist on a remote filesystem such
as NFS, AFS, or Windows SMB. Berkeley DB requires that the underlying filesystem implement strict POSIX locking semantics, and more importantly, the ability to map files directly
into process memory. Almost no network filesystems provide these features. If you attempt to
use Berkeley DB on a network share, the results are unpredictable—you may see mysterious
errors right away, or it may be months before you discover that your repository database is subtly corrupted.
If you need multiple computers to access the repository, you should set up a server process
(such as Apache or svnserve), store the repository on a local filesystem which the server can
access, and make the repository available over a network. Chapter 6, Server Configuration covers this process in detail.
You may have noticed that the path argument to svnadmin was just a regular filesystem path and not a
URL like the svn client program uses when referring to repositories. Both svnadmin and svnlook are
considered server-side utilities—they are used on the machine where the repository resides to examine
or modify aspects of the repository, and are in fact unable to perform tasks across a network. A common
mistake made by Subversion newcomers is trying to pass URLs (even "local" file: ones) to these two
So, after you've run the svnadmin create command, you have a shiny new Subversion repository in its
own directory. Let's take a peek at what is actually created inside that subdirectory.
$ ls repos
dav/ db/ format
With the exception of the README.txt and format files, the repository directory is a collection of
subdirectories. As in other areas of the Subversion design, modularity is given high regard, and hierarchical organization is preferred to cluttered chaos. Here is a brief description of all of the items you see
in your new repository directory:
A directory provided to Apache and mod_dav_svn for their private housekeeping data.
The main Berkeley DB environment, full of DB tables that comprise the data store for
Subversion's filesystem (where all of your versioned data resides).
A file whose contents are a single integer value that dictates the version number of the
repository layout.
A directory full of hook script templates (and hook scripts themselves, once you've in61
Repository Administration
stalled some).
A directory for Subversion's repository locking data, used for tracking accessors to the
A file which merely informs its readers that they are looking at a Subversion repository.
In general, you shouldn't tamper with your repository “by hand”. The svnadmin tool should be sufficient for any changes necessary to your repository, or you can look to third-party tools (such as Berkeley
DB's tool suite) for tweaking relevant subsections of the repository. Some exceptions exist, though, and
we'll cover those here.
Hook Scripts
A hook is a program triggered by some repository event, such as the creation of a new revision or the
modification of an unversioned property. Each hook is handed enough information to tell what that
event is, what target(s) it's operating on, and the username of the person who triggered the event. Depending on the hook's output or return status, the hook program may continue the action, stop it, or suspend it in some way.
The hooks subdirectory is, by default, filled with templates for various repository hooks.
$ ls repos/hooks/
There is one template for each hook that the Subversion repository implements, and by examining the
contents of those template scripts, you can see what triggers each such script to run and what data is
passed to that script. Also present in many of these templates are examples of how one might use that
script, in conjunction with other Subversion-supplied programs, to perform common useful tasks. To actually install a working hook, you need only place some executable program or script into the repos/
hooks directory which can be executed as the name (like start-commit or post-commit) of the hook.
On Unix platforms, this means supplying a script or program (which could be a shell script, a Python
program, a compiled C binary, or any number of other things) named exactly like the name of the hook.
Of course, the template files are present for more than just informational purposes—the easiest way to
install a hook on Unix platforms is to simply copy the appropriate template file to a new file that lacks
the .tmpl extension, customize the hook's contents, and ensure that the script is executable. Windows,
however, uses file extensions to determine whether or not a program is executable, so you would need to
supply a program whose basename is the name of the hook, and whose extension is one of the special
extensions recognized by Windows for executable programs, such as .exe or .com for programs, and
.bat for batch files.
Currently there are five hooks implemented by the Subversion repository:
This is run before the commit transaction is even created. It is typically
used to decide if the user has commit privileges at all. The repository
passes two arguments to this program: the path to the repository, and
username which is attempting the commit. If the program returns a nonzero exit value, the commit is stopped before the transaction is even created.
This is run when the transaction is complete, but before it is committed.
Repository Administration
Typically, this hook is used to protect against commits that are disallowed due to content or location (for example, your site might require
that all commits to a certain branch include a ticket number from the bug
tracker, or that the incoming log message is non-empty). The repository
passes two arguments to this program: the path to the repository, and the
name of the transaction being committed. If the program returns a nonzero exit value, the commit is aborted and the transaction is removed.
The Subversion distribution includes some access control scripts (located
in the tools/hook-scripts directory of the Subversion source tree)
that can be called from pre-commit to implement fine-grained access
control. At this time, this is the only method by which administrators can
implement finer-grained access control beyond what Apache's
httpd.conf offers. In a future version of Subversion, we plan to implement access control lists (ACLs) directly in the filesystem.
This is run after the transaction is committed, and a new revision is created. Most people use this hook to send out descriptive emails about the
commit or to make a backup of the repository. The repository passes two
arguments to this program: the path to the repository, and the new revision number that was created. The exit code of the program is ignored.
The Subversion distribution includes a script (located
in the tools/hook-scripts/ directory of the Subversion source
tree) that can be used to send email with (and/or append to a log file) a
description of a given commit. This mail contains a list of the paths that
were changed, the log message attached to the commit, the author and
date of the commit, as well as a GNU diff-style display of the changes
made to the various versioned files as part of the commit.
Another useful tool provided by Subversion is the script
(located in the tools/backup/ directory of the Subversion source
tree). This script performs hot backups of your Subversion repository (a
feature supported by the Berkeley DB database back-end), and can be
used to make a per-commit snapshot of your repository for archival or
emergency recovery purposes.
Because Subversion's revision properties are not versioned, making modifications to such a property (for example, the svn:log commit message property) will overwrite the previous value of that property forever.
Since data can be potentially lost here, Subversion supplies this hook
(and its counterpart, post-revprop-change) so that repository administrators can keep records of changes to these items using some external means if they so desire.
This hook runs just before such a modification is made to the repository.
The repository passes four arguments to this hook: the path to the repository, the revision on which the to-be-modified property exists, the authenticated username of the person making the change, and the name of
the property itself.
As mentioned earlier, this hook is the counterpart of the prerevprop-change hook. In fact, for the sake of paranoia this script
will not run unless the pre-revprop-change hook exists. When
both of these hooks are present, the post-revprop-change hook
runs just after a revision property has been changed, and is typically used
to send an email containing the new value of the changed property. The
repository passes four arguments to this hook: the path to the repository,
Repository Administration
the revision on which the property exists, the authenticated username of
the person making the change, and the name of the property itself.
The Subversion distribution includes a script
(located in the tools/hook-scripts/ directory of the Subversion
source tree) that can be used to send email with (and/or append to a log
file) the details of a revision property change. This mail contains the revision and name of the changed property, the user who made the change,
and the new property value.
Subversion will attempt to execute hooks as the same user who owns the process which is accessing the
Subversion repository. In most cases, the repository is being accessed via Apache HTTP server and
mod_dav_svn, so this user is the same user that Apache runs as. The hooks themselves will need to be
configured with OS-level permissions that allow that user to execute them. Also, this means that any file
or programs (including the Subversion repository itself) accessed directly or indirectly by the hook will
be accessed as the same user. In other words, be alert to potential permission-related problems that could
prevent the hook from performing the tasks you've written it to perform.
Berkeley DB Configuration
A Berkeley DB environment is an encapsulation of one or more databases, log files, region files and
configuration files. The Berkeley DB environment has it own set of default configuration values for
things like the number of locks allowed to be taken out at any given time, or the maximum size of the
journaling log files, etc. Subversion's filesystem code additionally chooses default values for some of the
Berkeley DB configuration options. However, sometimes your particular repository, with its unique collection of data and access patterns, might require a different set of configuration option values.
The folks at Sleepycat (the producers of Berkeley DB) understand that different databases have different
requirements, and so they have provided a mechanism for overriding at runtime many of the configuration values for the Berkeley DB environment. Berkeley checks for the presence of a file named
DB_CONFIG in each environment directory, and parses the options found in that file for use with that
particular Berkeley environment.
The Berkeley configuration file for your repository is located in the db environment directory, at repos/db/DB_CONFIG. Subversion itself creates this file when it creates the rest of the repository. The
file initially contains some default options, as well as pointers to the Berkeley DB online documentation
so you can read about what those options do. Of course, you are free to add any of the supported Berkeley DB options to your DB_CONFIG file. Just be aware that while Subversion never attempts to read or
interpret the contents of the file, and makes no use of the option settings in it, you'll want to avoid any
configuration changes that may cause Berkeley DB to behave in a fashion that is unexpected by the rest
of the Subversion code. Also, changes made to DB_CONFIG won't take effect until you recover the
database environment (using svnadmin recover).
Repository Maintenance
An Administrator's Toolkit
svnlook is a tool provided by Subversion for examining the various revisions and transactions in a
repository. No part of this program attempts to change the repository—it's a “read-only” tool. svnlook is
typically used by the repository hooks for reporting the changes that are about to be committed (in the
case of the pre-commit hook) or that were just committed (in the case of the post-commit hook) to the
repository. A repository administrator may use this tool for diagnostic purposes.
Repository Administration
svnlook has a straightforward syntax:
$ svnlook help
general usage: svnlook SUBCOMMAND REPOS_PATH [ARGS & OPTIONS ...]
Note: any subcommand which takes the '--revision' and '--transaction'
options will, if invoked without one of those options, act on
the repository's youngest revision.
Type "svnlook help <subcommand>" for help on a specific subcommand.
Nearly every one of svnlook's subcommands can operate on either a revision or a transaction tree, printing information about the tree itself, or how it differs from the previous revision of the repository. You
use the --revision and --transaction options to specify which revision or transaction, respectively, to examine. Note that while revision numbers appear as natural numbers, transaction names are
alphanumeric strings. Keep in mind that the filesystem only allows browsing of uncommitted transactions (transactions that have not resulted in a new revision). Most repositories will have no such transactions, because transactions are usually either committed (which disqualifies them from viewing) or
aborted and removed.
In the absence of both the --revision and --transaction options, svnlook will examine the
youngest (or “HEAD”) revision in the repository. So the following two commands do exactly the same
thing when 19 is the youngest revision in the repository located at /path/to/repos:
$ svnlook info /path/to/repos
$ svnlook info /path/to/repos --revision 19
The only exception to these rules about subcommands is the svnlook youngest subcommand, which
takes no options, and simply prints out the HEAD revision number.
$ svnlook youngest /path/to/repos
Output from svnlook is designed to be both human- and machine-parsable. Take as an example the output of the info subcommand:
$ svnlook info path/to/repos
2002-11-04 09:29:13 -0600 (Mon, 04 Nov 2002)
Added the usual
Greek tree.
The output of the info subcommand is defined as:
The author, followed by a newline.
The date, followed by a newline.
The number of characters in the log message, followed by a newline.
The log message itself, followed by a newline.
Repository Administration
This output is human-readable, meaning items like the datestamp are displayed using a textual representation instead of something more obscure (such as the number of nanoseconds since the Tasty Freeze
guy drove by). But this output is also machine-parsable—because the log message can contain multiple
lines and be unbounded in length, svnlook provides the length of that message before the message itself.
This allows scripts and other wrappers around this command to make intelligent decisions about the log
message, such as how much memory to allocate for the message, or at least how many bytes to skip in
the event that this output is not the last bit of data in the stream.
Another common use of svnlook is to actually view the contents of a revision or transaction tree. The
svnlook tree command displays the directories and files in the requested tree. If you supply the -show-ids option, it will also show the filesystem node revision IDs for each of those paths (which is
generally of more use to developers than to users).
$ svnlook tree path/to/repos --show-ids
/ <0.0.1>
A/ <2.0.1>
B/ <4.0.1>
lambda <5.0.1>
E/ <6.0.1>
alpha <7.0.1>
beta <8.0.1>
F/ <9.0.1>
mu <3.0.1>
C/ <a.0.1>
D/ <b.0.1>
gamma <c.0.1>
G/ <d.0.1>
pi <e.0.1>
rho <f.0.1>
tau <g.0.1>
H/ <h.0.1>
chi <i.0.1>
omega <k.0.1>
psi <j.0.1>
iota <1.0.1>
Once you've seen the layout of directories and files in your tree, you can use commands like svnlook
cat, svnlook propget, and svnlook proplist to dig into the details of those files and directories.
svnlook can perform a variety of other queries, displaying subsets of bits of information we've mentioned previously, reporting which paths were modified in a given revision or transaction, showing textual and property differences made to files and directories, and so on. The following is a brief description of the current list of subcommands accepted by svnlook, and the output of those subcommands:
Print the tree's author.
Print the contents of a file in the tree.
List all files and directories that changed in the tree.
Print the tree's datestamp.
Print unified diffs of changed files.
List the directories in the tree that were themselves changed, or whose file children
were changed.
Display interesting points in the history of a versioned path (places where modifica66
Repository Administration
tions or copies occurred).
Print the tree's author, datestamp, log message character count, and log message.
Print the tree's log message.
Print the value of a property on a path in the tree.
Print the names and values of properties set on paths in the tree.
Print the tree listing, optionally revealing the filesystem node revision IDs associated with each path.
Print the tree's unique user ID (UUID).
Print the youngest revision number.
The svnadmin program is the repository administrator's best friend. Besides providing the ability to create Subversion repositories, this program allows you to perform several maintenance operations on those
repositories. The syntax of svnadmin is similar to that of svnlook:
$ svnadmin help
general usage: svnadmin SUBCOMMAND REPOS_PATH [ARGS & OPTIONS ...]
Type "svnadmin help <subcommand>" for help on a specific subcommand.
Available subcommands:
help (?, h)
We've already mentioned svnadmin's create subcommand (see the section called “Repository Creation and Configuration”). Most of the others we will cover in more detail later in this chapter. For now,
let's just take a quick glance at what each of the available subcommands offers.
Creates a new Subversion repository.
Run over a specified revision range, performing predecessor deltification
on the paths changed in those revisions. If no revisions are specified, this
command will simply deltify the HEAD revision.
Dumps the contents of the repository, bounded by a given set of revisions,
using a portable dump format.
Makes a hot copy of a repository. You can run this command at any time
and make a safe copy of the repository, regardless if other processes are
using the repository.
Lists the paths of Berkeley DB log files associated with the repository.
This list includes all log files—those still in use by Subversion, as well as
those no longer in use.
Lists the paths of Berkeley DB log files associated with, but no longer used
Repository Administration
by, the repository. You may safely remove these log files from the repository layout, possibly archiving them for use in the event that you ever need
to perform a catastrophic recovery of the repository.
Loads a set of revisions into a repository from a stream of data that uses
the same portable dump format generated by the dump subcommand.
List the names of uncommitted Subversion transactions that currently exist
in the repository.
Perform recovery steps on a repository that is in need of such, generally after a fatal error has occurred that prevented a process from cleanly shutting
down its communication with the repository.
Cleanly remove Subversion transactions from the repository (conveniently
fed by output from the lstxns subcommand).
Replace the current value of the svn:log (commit log message) property
on a given revision in the repository with a new value.
Verify the contents of the repository. This includes, among other things,
checksum comparisons of the versioned data stored in the repository.
Since Subversion stores everything in an opaque database system, attempting manual tweaks is unwise,
if not quite difficult. And once data has been stored in your repository, Subversion generally doesn't really provide an easy way to remove that data. 13 But inevitably, there will be times when you would like
to manipulate the history of your repository. You might need to strip out all instances of a file that was
accidentally added to the repository (and shouldn't be there for whatever reason). Or, perhaps you have
multiple projects sharing a single repository, and you decide to split them up into their own repositories.
To accomplish tasks like this, administrators need an more manageable and malleable representation of
the data in their repositories—the Subversion repository dump format.
The Subversion repository dump format is a human-readable representation of the changes that you've
made to your versioned data over time. You use the svnadmin dump command to generate the dump
data, and svnadmin load to populate a new repository with it (see the section called “Migrating a
Repository”). The great thing about the human-readibility aspect of the dump format is that, if you aren't
careless about it, you can manually inspect and modify it. Of course, the downside is that if you have
two years' worth of repository activity encapsulated in what is likely to be a very large dumpfile, it could
take you a long, long time to manually inspect and modify it.
While it won't be the most commonly used tool at the administrator's disposal, svndumpfilter provides
a very particular brand of useful functionality—the ability to quickly and easily modify that dumpfile
data by acting as a path-based filter. Simply give it either a list of paths you wish to keep, or a list of
paths you wish to not keep, then pipe your repository dump data through this filter. The result will be a
modified stream of dump data that contains only the versioned paths you (explicitly or implicitly) requested.
The syntax of svndumpfilter is as follows:
$ svndumpfilter help
general usage: svndumpfilter SUBCOMMAND [ARGS & OPTIONS ...]
Type "svndumpfilter help <subcommand>" for help on a specific subcommand.
Available subcommands:
That, by the way, is a feature, not a bug.
Repository Administration
help (?, h)
There are only two interesting subcommands. They allow you to make the choice between explicit or
implicit inclusion of paths in the stream:
Filter out a set of paths from the dump data stream.
Allow only the requested set of paths to pass through the dump data stream.
Let's look a realistic example of how you might use this program. We discuss elsewhere (see the section
called “Choosing a Repository Layout”) the process of deciding how to choose a layout for the data in
your repositories—using one repository per project or combining them, arranging stuff within your
repository, and so on. But sometimes after new revisions start flying in, you rethink your layout and
would like to make some changes. A common change is the decision to move multiple projects which
are sharing a single repository into a single repository for each project.
Our imaginary repository contains three projects: calc, calendar, and spreadsheet. They have
been living side-by-side in a layout like this:
To get these three projects into their own repositories, we first make a dumpfile of the whole repository:
svnadmin dump /path/to/repos > repos-dumpfile
Dumped revision 0.
Dumped revision 1.
Dumped revision 2.
Dumped revision 3.
Next, run that dumpfile through the filter, each time including only one of our top-level directories, and
resulting in three new dumpfiles:
$ cat repos-dumpfile | svndumpfilter include calc > calc-dumpfile
$ cat repos-dumpfile | svndumpfilter include calendar > cal-dumpfile
$ cat repos-dumpfile | svndumpfilter include spreadsheet > ss-dumpfile
Repository Administration
At this point, you have to make a decision. Each of your dumpfiles at this point will create a valid repository, but will preserve the paths exactly as they were in the original repository. This means that even
though you would have a repository solely for your calc project, that repository would still have a toplevel directory named calc. If you want your trunk, tags, and branches directories to live in root
of your repository, you might wish to edit your dumpfiles, tweaking the Node-path and Copyfrompath headers to no longer have that first calc/ path component. Also, you'll want to remove the section of dump data that creates the calc directory. It will look something like:
Node-path: calc
Node-action: add
Node-kind: dir
Content-length: 0
All that remains now is to create your three new repositories, and load each dumpfile into the right
$ svnadmin create calc; svnadmin load calc < calc-dumpfile
<<< Started new transaction, based on original revision 1
* adding path : Makefile ... done.
* adding path : button.c ... done.
$ svnadmin create calendar; svnadmin load calendar < cal-dumpfile
<<< Started new transaction, based on original revision 1
* adding path : Makefile ... done.
* adding path : cal.c ... done.
$ svnadmin create spreadsheet; svnadmin load spreadsheet < ss-dumpfile
<<< Started new transaction, based on original revision 1
* adding path : Makefile ... done.
* adding path : ss.c ... done.
Both of svndumpfilter's subcommands accept options for deciding how to deal with “empty” revisions.
If a given revision contained only changes to paths that were filtered out, that now-empty revision could
be considered uninteresting or even unwanted. So to give the user control over what to do with those revisions, svndumpfilter provides the following command-line options:
Do not generate empty revisions at all—just omit them.
If empty revisions are dropped (using the --drop-empty-revs option), change the revision numbers of the remaining revisions so that
there are no gaps in the numeric sequence.
If empty revisions are not dropped, preserve the revision properties (log
message, author, date, custom properties, etc.) for those empty revisions.
Otherwise, empty revisions will only contain the original datestamp, and
a generated log message that indicates that this revision was emptied by
While svndumpfilter can be very useful, and a huge timesaver, there are unfortunately a couple of
gotchas. First, this utility is overly sensitive to path semantics. Pay attention to whether paths in your
dumpfile are specified with or without leading slashes. You'll want to look at the Node-path and
Repository Administration
Copyfrom-path headers.
Node-path: spreadsheet/Makefile
If the paths lack leading slashes, you should not include leading slashes in the paths you pass to svndumpfilter include and svndumpfilter exclude (and if they do, you should). Further, if your dumpfile
has an inconsistent usage of leading slashes for some reason, 14 you should probably normalize those
paths to either all have, or all lack, leading slashes.
Also, copied paths can give you some trouble. Subversion supports copy operations in the repository,
where a new path is created by copying some already existing path. It is possible that at some point in
the lifetime of your repository, you might have copied a file or directory from some location that svndumpfilter is excluding, to a location that it is including. In order to make the dump data self-sufficient,
svndumpfilter needs to still show the addition of the new path—including the contents of any files created by the copy—and not represent that addition as a copy from a source that won't exist in your filtered dump data stream. But because the Subversion repository dump format only shows what was
changed in each revision, the contents of the copy source might not be readily available. If you suspect
that you have any copies of this sort in your repository, you might want to rethink your set of included/
excluded paths.
The Subversion source tree also comes with a shell-like interface to the repository. The
Python script (located in tools/examples/ in the source tree) uses Subversion's language bindings
(so you must have those properly compiled and installed in order for this script to work) to connect to
the repository and filesystem libraries.
Once started, the program behaves similarly to a shell program, allowing you to browse the various directories in your repository. Initially, you are “positioned” in the root directory of the HEAD revision of
the repository, and presented with a command prompt. You can use the help command at any time to
display a list of available commands and what they do.
$ /path/to/repos
<rev: 2 />$ help
Available commands:
cat FILE
: dump the contents of FILE
cd DIR
: change the current working directory to DIR
: exit the shell
ls [PATH]
: list the contents of the current directory
: list the transactions available for browsing
setrev REV
: set the current revision to browse
settxn TXN
: set the current transaction to browse
: list the youngest browsable revision number
<rev: 2 />$
Navigating the directory structure of your repository is done in the same way you would navigate a regular Unix or Windows shell—using the cd command. At all times, the command prompt will show you
what revision (prefixed by rev:) or transaction (prefixed by txn:) you are currently examining, and at
what path location in that revision or transaction. You can change your current revision or transaction
with the setrev and settxn commands, respectively. As in a Unix shell, you can use the ls command to display the contents of the current directory, and you can use the cat command to display the
contents of a file.
While svnadmin dump has a consistent leading slash policy—to not include them—other programs which generate dump data
might not be so consistent.
Repository Administration
Example 5.1. Using svnshell to Navigate the Repository
<rev: 2 />$ ls
sally <
Nov 15 11:50 A/
harry <
56 Nov 19 08:19 iota
<rev: 2 />$ cd A
<rev: 2 /A>$ ls
sally <
Nov 15 11:50 B/
sally <
Nov 15 11:50 C/
sally <
Nov 15 11:50 D/
sally <
23 Nov 15 11:50 mu
<rev: 2 /A>$ cd D/G
<rev: 2 /A/D/G>$ ls
sally <
23 Nov 15 11:50 pi
sally <
24 Nov 15 11:50 rho
sally <
24 Nov 15 11:50 tau
<rev: 2 /A>$ cd ../..
<rev: 2 />$ cat iota
This is the file 'iota'.
Added this text in revision 2.
<rev: 2 />$ setrev 1; cat iota
This is the file 'iota'.
<rev: 1 />$ exit
As you can see in the previous example, multiple commands may be specified at a single command
prompt, separated by a semicolon. Also, the shell understands the notions of relative and absolute paths,
and will properly handle the "." and ".." special path components.
The youngest command displays the youngest revision. This is useful for determining the range of
valid revisions you can use as arguments to the setrev command—you are allowed to browse all the
revisions (recalling that they are named with integers) between 0 and the youngest, inclusively. Determining the valid browsable transactions isn't quite as pretty. Use the lstxns command to list the transactions that you are able to browse. The list of browsable transactions is the same list that svnadmin
lstxns returns, and the same list that is valid for use with svnlook's --transaction option.
Once you've finished using the shell, you can exit cleanly by using the exit command. Alternatively, you
can supply an end-of-file character—Control-D (though some Win32 Python distributions use the Windows Control-Z convention instead).
Berkeley DB Utilities
All of your versioned filesystem's structure and data live in a set of Berkeley DB database tables within
the db subdirectory of your repository. This subdirectory is a regular Berkeley DB environment directory, and can therefore be used in conjunction with any of Berkeley's database tools (you can see the
documentation for these tools at SleepyCat's website,
For day-to-day Subversion use, these tools are unnecessary. Most of the functionality typically needed
Repository Administration
for Subversion repositories has been duplicated in the svnadmin tool. For example, svnadmin listunused-dblogs and svnadmin list-dblogs perform a subset of what is provided by Berkeley's
db_archive command, and svnadmin recover reflects the common use-cases of the db_recover utility.
There are still a few Berkeley DB utilities that you mind find useful. The db_dump and db_load programs write and read, respectively, a custom file format which describes the keys and values in a Berkeley DB database. Since Berkeley databases are not portable across machine architectures, this format is a
useful way to transfer those databases from machine to machine, irrespective of architecture or operating
system. Also, the db_stat utility can provide useful information about the status of your Berkeley DB
environment, including detailed statistics about the locking and storage subsystems.
Repository Cleanup
Your Subversion repository will generally require very little attention once it is configured to your liking. However, there are times when some manual assistance from an administrator might be in order.
The svnadmin utility provides some helpful functionality to assist you in performing such tasks as
modifying commit log messages,
removing dead transactions,
recovering “wedged” repositories, and
migrating repository contents to a different repository.
Perhaps the most commonly used of svnadmin's subcommands is setlog. When a transaction is committed to the repository and promoted to a revision, the descriptive log message associated with that new
revision (and provided by the user) is stored as an unversioned property attached to the revision itself. In
other words, the repository remembers only the latest value of the property, and discards previous ones.
Sometimes a user will have an error in her log message (a misspelling or some misinformation, perhaps). If the repository is configured (using the pre-revprop-change and postrevprop-change hooks; see the section called “Hook Scripts”) to accept changes to this log message
after the commit is finished, then the user can “fix” her log message remotely using the svn program's
propset command (see Chapter 9, Subversion Complete Reference). However, because of the potential to lose information forever, Subversion repositories are not, by default, configured to allow changes
to unversioned properties—except by an administrator.
If a log message needs to be changed by an administrator, this can be done using svnadmin setlog. This
command changes the log message (the svn:log property) on a given revision of a repository, reading
the new value from a provided file.
$ echo "Here is the new, correct log message" > newlog.txt
$ svnadmin setlog myrepos newlog.txt -r 388
The svnadmin setlog command alone is still bound by the same protections against modifying unversioned properties as a remote client is—the pre- and post-revprop-change hooks are still triggered, and therefore must be setup to accept changes of this nature. But an administrator can get around
these protections by passing the --bypass-hooks option to svnadmin setlog command.
Remember, though, that by bypassing the hooks, you are likely avoiding such things as email
notifications of property changes, backup systems which track unversioned property changes,
and so on. In other words, be very careful about what you are changing, and how you change it.
Repository Administration
Another common use of svnadmin is to query the repository for outstanding—possibly Subverdead—sion transactions. In the event that a commit should fail, the transaction is usually cleaned up.
That is, the transaction itself is removed from the repository, and any data associated with (and only
with) that transaction is removed as well. Occasionally, though, a failure occurs in such a way that the
cleanup of the transaction never happens. This could happen for several reasons: perhaps the client operation was inelegantly terminated by the user, or a network failure might have occurred in the middle of
an operation, etc. Regardless of the reason, these dead transactions serve only to clutter the repository
and consume resources.
You can use svnadmin's lstxns command to list the names of the currently outstanding transactions.
$ svnadmin lstxns myrepos
Each item in the resultant output can then be used with svnlook (and its --transaction option) to
determine who created the transaction, when it was created, what types of changes were made in the
transaction—in other words, whether or not the transaction is a safe candidate for removal! If so, the
transaction's name can be passed to svnadmin rmtxns, which will perform the cleanup of the transaction. In fact, the rmtxns subcommand can take its input directly from the output of lstxns!
$ svnadmin rmtxns myrepos `svnadmin lstxns myrepos`
If you use these two subcommands like this, you should consider making your repository temporarily inaccessible to clients. That way, no one can begin a legitimate transaction before you start your cleanup.
The following is a little bit of shell-scripting that can quickly generate information about each outstanding transaction in your repository:
Example 5.2. (Reporting Outstanding Transactions)
### Generate informational output for all outstanding transactions in
### a Subversion repository.
if [ "x$REPOS" = x ] ; then
echo "usage: $0 REPOS_PATH"
for TXN in `${SVNADMIN} lstxns ${REPOS}`; do
echo "---[ Transaction ${TXN} ]-------------------------------------------"
${SVNLOOK} info "${REPOS}" --transaction "${TXN}"
Repository Administration
You can run the previous script using /path/to/ /path/to/repos. The output is basically a concatenation of several chunks of svnlook info output (see the section called “svnlook”), and will look
something like:
$ myrepos
---[ Transaction 19 ]------------------------------------------sally
2001-09-04 11:57:19 -0500 (Tue, 04 Sep 2001)
---[ Transaction 3a1 ]------------------------------------------harry
2001-09-10 16:50:30 -0500 (Mon, 10 Sep 2001)
Trying to commit over a faulty network.
---[ Transaction a45 ]------------------------------------------sally
2001-09-12 11:09:28 -0500 (Wed, 12 Sep 2001)
Usually, if you see a dead transaction that has no log message attached to it, this is the result of a failed
update (or update-like) operation. These operations use Subversion transactions under the hood to mimic
working copy state. Since they are never intended to be committed, Subversion doesn't require a log
message for those transactions. Transactions that do have log messages attached are almost certainly
failed commits of some sort. Also, a transaction's datestamp can provide interesting information—for
example, how likely is it that an operation begun nine months ago is still active?
In short, transaction cleanup decisions need not be made unwisely. Various sources of ininformation—cluding Apache's error and access logs, the logs of successful Subversion commits, and so
on—can be employed in the decision-making process. Finally, an administrator can often simply communicate with a seemingly dead transaction's owner (via email, for example) to verify that the transaction is, in fact, in a zombie state.
Managing Disk Space
While the cost of storage has dropped incredibly in the past few years, disk usage is still a valid concern
for administrators seeking to version large amounts of data. Every additional byte consumed by the live
repository is a byte that needs to be backed up offsite, perhaps multiple time as part of rotating backup
schedules. Since the primary storage mechanism of a Subversion repository is a complex database system, it is useful to know what pieces of data need to remain on the live site, which need to be backed up,
and which can be safely removed.
Until recently, the largest offender of disk space usage with respect to Subversion repositories was the
logfiles to which Berkeley DB performs its pre-writes before modifying the actual database files. These
files capture all the actions taken along the route of changing the database from one state to
another—while the database files reflect at any given time some state, the logfiles contain all the many
changes along the way between states. As such, they can start to accumulate quite rapidly.
Fortunately, beginning with the 4.2 release of Berkeley DB, the database environment has the ability to
remove its own unused logfiles without any external procedures. Any repositories created using an svnadmin which is compiled against Berkeley DB version 4.2 or greater will be configured for this automatic log file removal. If you don't want this feature enabled, simply pass the --bdb-log-keep option to the svnadmin create command. If you forget to do this, or change your mind at a later time, simple edit the DB_CONFIG file found in your repository's db directory, comment out the line which contains the set_flags DB_LOG_AUTOREMOVE directive, and then run svnadmin recover on your
repository to force the configuration changes to take effect. See the section called “Berkeley DB Configuration” for more information about database configuration.
Repository Administration
Without some sort of automatic log file removal in place, log files will accumulate as you use your
repository. This is actually somewhat of a feature of the database system—you should be able to recreate your entire database using nothing but the log files, so these files can be useful for catastrophic
database recovery. But typically, you'll want to archive the log files that are no longer in use by Berkeley DB, and then remove them from disk to conserve space. Use the svnadmin list-unused-dblogs command to list the unused logfiles:
$ svnadmin list-unused-dblogs /path/to/repos
$ svnadmin list-unused-dblogs /path/to/repos | xargs rm
## disk space reclaimed!
Repository Recovery
In order to protect the data in your repository, the database back-end uses a locking mechanism. This
mechanism ensures that portions of the database are not simultaneously modified by multiple database
accessors, and that each process sees the data in the correct state when that data is being read from the
database. When a process needs to change something in the database, it first checks for the existence of
a lock on the target data. If the data is not locked, the process locks the data, makes the change it wants
to make, and then unlocks the data. Other processes are forced to wait until that lock is removed before
they are permitted to continue accessing that section of the database.
In the course of using your Subversion repository, fatal errors (such as running out of disk space or
available memory) or interruptions can prevent a process from having the chance to remove the locks it
has placed in the database. The result is that the back-end database system gets “wedged”. When this
happens, any attempts to access the repository hang indefinitely (since each new accessor is waiting for
a lock to go away—which isn't going to happen).
First, if this happens to your repository, don't panic. Subversion's filesystem takes advantage of database
transactions and checkpoints and pre-write journaling to ensure that only the most catastrophic of events
15 can permanently destroy a database environment. A sufficiently paranoid repository administrator
will be making off-site backups of the repository data in some fashion, but don't call your system administrator to restore a backup tape just yet.
Secondly, use the following recipe to attempt to “unwedge” your repository:
Make sure that there are no processes accessing (or attempting to access) the repository. For networked repositories, this means shutting down the Apache HTTP Server, too.
Become the user who owns and manages the repository.
Run the command svnadmin recover /path/to/repos. You should see output like this:
Please wait; recovering the repository may take some time...
Recovery completed.
The latest repos revision is 19.
This command may take many minutes to complete.
Restart the Subversion server.
E.g.: hard drive + huge electromagnet = disaster.
Repository Administration
This procedure fixes almost every case of repository lock-up. Make sure that you run this command as
the user that owns and manages the database, not just as root. Part of the recovery process might involve recreating from scratch various database files (shared memory regions, for example). Recovering
as root will create those files such that they are owned by root, which means that even after you restore connectivity to your repository, regular users will be unable to access it.
If the previous procedure, for some reason, does not successfully unwedge your repository, you should
do two things. First, move your broken repository out of the way and restore your latest backup of it.
Then, send an email to the Subversion developer list (at <>) describing your problem in detail. Data integrity is an extremely high priority to the Subversion developers.
Migrating a Repository
A Subversion filesystem has its data spread throughout various database tables in a fashion generally understood by (and of interest to) only the Subversion developers themselves. However, circumstances
may arise that call for all, or some subset, of that data to be collected into a single, portable, flat file format. Subversion provides such a mechanism, implemented in a pair of svnadmin subcommands: dump
and load.
The most common reason to dump and load a Subversion repository is due to changes in Subversion itself. As Subversion matures, there are times when certain changes made to the back-end database
schema cause Subversion to be incompatible with previous versions of the repository. The recommended course of action when you are upgrading across one of those compatibility boundaries is a relatively simple process:
Using your current version of svnadmin, dump your repositories to dump files.
Upgrade to the new version of Subversion.
Move your old repositories out of the way, and create new empty ones in their place using your
new svnadmin.
Again using your new svnadmin, load your dump files into their respective, just-created repositories.
Finally, be sure to copy any customizations from your old repositories to the new ones, including
DB_CONFIG files and hook scripts. You'll want to pay attention to the release notes for the new release of Subversion to see if any changes since your last upgrade affect those hooks or configuration options.
svnadmin dump will output a range of repository revisions that are formatted using Subversion's custom filesystem dump format. The dump format is printed to the standard output stream, while informative messages are printed to the standard error stream. This allows you to redirect the output stream to a
file while watching the status output in your terminal window. For example:
$ svnlook youngest myrepos
$ svnadmin dump myrepos > dumpfile
* Dumped revision 0.
* Dumped revision 1.
* Dumped revision 2.
* Dumped revision 25.
* Dumped revision 26.
Repository Administration
At the end of the process, you will have a single file (dumpfile in the previous example) that contains
all the data stored in your repository in the requested range of revisions. Note that svnadmin dump is
reading revision trees from the repository just like any other "reader" process would (svn checkout, for
example.) So it's safe to run this command at any time.
The other subcommand in the pair, svnadmin load, parses the standard input stream as a Subversion
repository dump file, and effectively replays those dumped revisions into the target repository for that
operation. It also gives informative feedback, this time using the standard output stream:
$ svnadmin load newrepos < dumpfile
<<< Started new txn, based on original revision 1
* adding path : A ... done.
* adding path : A/B ... done.
------- Committed new rev 1 (loaded from original rev 1) >>>
<<< Started new txn, based on original revision 2
* editing path : A/mu ... done.
* editing path : A/D/G/rho ... done.
------- Committed new rev 2 (loaded from original rev 2) >>>
<<< Started new txn, based on original revision 25
* editing path : A/D/gamma ... done.
------- Committed new rev 25 (loaded from original rev 25) >>>
<<< Started new txn, based on original revision 26
* adding path : A/Z/zeta ... done.
* editing path : A/mu ... done.
------- Committed new rev 26 (loaded from original rev 26) >>>
Note that because svnadmin uses standard input and output streams for the repository dump and load
process, people who are feeling especially saucy can try things like this (perhaps even using different
versions of svnadmin on each side of the pipe):
$ svnadmin create newrepos
$ svnadmin dump myrepos | svnadmin load newrepos
We mentioned previously that svnadmin dump outputs a range of revisions. Use the --revision option to specify a single revision to dump, or a range of revisions. If you omit this option, all the existing
repository revisions will be dumped.
$ svnadmin dump myrepos --revision 23 > rev-23.dumpfile
$ svnadmin dump myrepos --revision 100:200 > revs-100-200.dumpfile
As Subversion dumps each new revision, it outputs only enough information to allow a future loader to
re-create that revision based on the previous one. In other words, for any given revision in the dump file,
only the items that were changed in that revision will appear in the dump. The only exception to this rule
is the first revision that is dumped with the current svnadmin dump command.
By default, Subversion will not express the first dumped revision as merely differences to be applied to
Repository Administration
the previous revision. For one thing, there is no previous revision in the dump file! And secondly, Subversion cannot know the state of the repository into which the dump data will be loaded (if it ever, in
fact, occurs). To ensure that the output of each execution of svnadmin dump is self-sufficient, the first
dumped revision is by default a full representation of every directory, file, and property in that revision
of the repository.
However, you can change this default behavior. If you add the --incremental option when you
dump your repository, svnadmin will compare the first dumped revision against the previous revision in
the repository, the same way it treats every other revision that gets dumped. It will then output the first
revision exactly as it does the rest of the revisions in the dump range—mentioning only the changes that
occurred in that revision. The benefit of this is that you can create several small dump files that can be
loaded in succession, instead of one large one, like so:
$ svnadmin dump myrepos --revision 0:1000 > dumpfile1
$ svnadmin dump myrepos --revision 1001:2000 --incremental > dumpfile2
$ svnadmin dump myrepos --revision 2001:3000 --incremental > dumpfile3
These dump files could be loaded into a new repository with the following command sequence:
$ svnadmin load newrepos < dumpfile1
$ svnadmin load newrepos < dumpfile2
$ svnadmin load newrepos < dumpfile3
Another neat trick you can perform with this --incremental option involves appending to an existing dump file a new range of dumped revisions. For example, you might have a post-commit hook
that simply appends the repository dump of the single revision that triggered the hook. Or you might
have a script that runs nightly to append dump file data for all the revisions that were added to the repository since the last time the script ran. Used like this, svnadmin's dump and load commands can be a
valuable means by which to backup changes to your repository over time in case of a system crash or
some other catastrophic event.
The dump format can also be used to merge the contents of several different repositories into a single
repository. By using the --parent-dir of svnadmin load, you can specify a new virtual root directory for the load process. That means if you have dumpfiles for three repositories, say calcdumpfile, cal-dumpfile, and ss-dumpfile, you can first create a new repository to hold them
$ svnadmin create /path/to/projects
Then, make new directories in the repository which will encapsulate the contents of each of the three
previous repositories:
$ svn mkdir -m "Initial project roots" \
file:///path/to/projects/calc \
file:///path/to/projects/calendar \
Committed revision 1.
Lastly, load the individual dumpfiles into their respective locations in the new repository:
$ svnadmin load /path/to/projects --parent-dir calc < calc-dumpfile
Repository Administration
$ svnadmin load /path/to/projects --parent-dir calendar < cal-dumpfile
$ svnadmin load /path/to/projects --parent-dir spreadsheet < ss-dumpfile
We'll mention one final way to use the Subversion repository dump format—conversion from a different
storage mechanism or version control system altogether. Because the dump file format is, for the most
part, human-readable, 16 it should be relatively easy to describe generic sets of changes—each of which
should be treated as a new revision—using this file format. In fact, the utility (see the section called “Repository Converters”) uses the dump format to represent the contents of a CVS repository
so that those contents can be moved in a Subversion repository.
Repository Backup
Despite numerous advances in technology since the birth of the modern computer, one thing unfortunately rings true with crystalline clarity—sometimes, things go very, very awry. Power outages, network
connectivity dropouts, corrupt RAM and crashed hard drives are but a taste of the evil that Fate is poised
to unleash on even the most conscientious administrator. And so we arrive at a very important
topic—how to make backup copies of your repository data.
There are generally two types of backup methods available for Subversion repository
administrators—incremental and full. We discussed in an earlier section of this chapter how to use svnadmin dump --incremental to perform an incremental backup (see the section called “Migrating a
Repository”). Essentially, the idea is to only backup at a given time the changes to the repository since
the last time you made a backup.
A full backup of the repository is quite literally a duplication of the entire repository directory (which includes the Berkeley database environment). Now, unless you temporarily disable all other access to your
repository, simply doing a recursive directory copy runs the risk of generating a faulty backup, since
someone might be currently writing to the database.
Fortunately, Sleepycat's Berkeley DB documents describe a certain order in which database files can be
copied that will guarantee a valid backup copy. And better still, you don't have to implement that algorithm yourself, because the Subversion development team has already done so. The
script is found in the tools/backup/ directory of the Subversion source distribution. Given a repository path and a backup location,—which is really just a more intelligent wrapper around
the svnadmin hotcopy command—will perform the necessary steps for backing up your live
repository—without requiring that you bar public repository access at all—and then will clean out the
dead Berkeley log files from your live repository.
Even if you also have an incremental backup, you might want to run this program on a regular basis. For
example, you might consider adding to a program scheduler (such as crond on Unix
systems). Or, if you prefer fine-grained backup solutions, you could have your post-commit hook script
call (see the section called “Hook Scripts”), which will then cause a new backup of your
repository to occur with every new revision created. Simply add the following to the hooks/
post-commit script in your live repository directory:
(cd /path/to/hook/scripts; ./ ${REPOS} /path/to/backups &)
The resulting backup is a fully functional Subversion repository, able to be dropped in as a replacement
for your live repository should something go horribly wrong.
There are benefits to both types of backup methods. The easiest is by far the full backup, which will always result in a perfect working replica of your repository. This again means that should something bad
The Subversion repository dump format resembles an RFC-822 format, the same type of format used for most email.
Repository Administration
happen to your live repository, you can restore from the backup with a simple recursive directory copy.
Unfortunately, if you are maintaining multiple backups of your repository, these full copies will each eat
up just as much disk space as your live repository.
Incremental backups using the repository dump format are excellent to have on hand if the database
schema changes between successive versions of Subversion itself. Since a full repository dump and load
are generally required to upgrade your repository to the new schema, it's very convenient to already have
half of that process (the dump part) finished. Unfortunately, the creation of—and restoration infrom—cremental backups takes longer, as each commit is effectively replayed into either the dumpfile
or the repository.
In either backup scenario, repository administrators need to be aware of how modifications to unversioned revision properties affect their backups. Since these changes do not themselves generate new revisions, they will not trigger post-commit hooks, and may not even trigger the pre-revprop-change and
post-revprop-change hooks. 17 And since you can change revision properties without respect to chronological order—you can change any revision's properties at any time—an incremental backup of the latest
few revisions might not catch a property modification to a revision that was included as part of a previous backup.
Generally speaking, only the truly paranoid would need to backup their entire repository, say, every time
a commit occurred. However, assuming that a given repository has some other redundancy mechanism
in place with relatively fine granularity (like per-commit emails), a hot backup of the database might be
something that a repository administrator would want to include as part of a system-wide nightly
backup. For most repositories, archived commit emails alone provide sufficient redundancy as restoration sources, at least for the most recernt few commits. But it's your data—protect it as much as you'd
Often, the best approach to repository backups is a diversified one. You can leverage combinations of
full and incremental backups, plus archives of commit emails. The Subversion developers, for example,
back up the Subversion source code repository after every new revision is created, and keep an archive
of all the commit and property change notification emails. Your solution might be similar, but should be
catered to your needs and that delicate balance of convenience with paranoia. And while all of this might
not save your hardware from the iron fist of Fate, 18 it should certainly help you recover from those trying times.
Adding Projects
Once your repository is created and configured, all that remains is to begin using it. If you have a collection of existing data that is ready to be placed under version control, you will more than likely want to
use the svn client program's import subcommand to accomplish that. Before doing this, though, you
should carefully consider your long-term plans for the repository. In this section, we will offer some advice on how to plan the layout of your repository, and how to get your data arranged in that layout.
Choosing a Repository Layout
While Subversion allows you to move around versioned files and directories without any loss of information, doing so can still disrupt the workflow of those who access the repository often and come to expect things to be at certain locations. Try to peer into the future a bit; plan ahead before placing your
data under version control. By “laying out” the contents of your repositories in an effective manner the
first time, you can prevent a load of future headaches.
There are a few things to consider when setting up Subversion repositories. Let's assume that as repository administrator, you will be responsible for supporting the version control system for several projects.
The first decision is whether to use a single repository for multiple projects, or to give each project its
svnadmin setlog can be called in a way that bypasses the hook interface altogether.
You know—the collective term for all of her “fickle fingers”.
Repository Administration
own repository, or some compromise of these two.
There are benefits to using a single repository for multiple projects, most obviously the lack of duplicated maintenance. A single repository means that there is one set of hook scripts, one thing to routinely
backup, one thing to dump and load if Subversion releases an incompatible new version, and so on.
Also, you can move data between projects easily, and without losing any historical versioning information.
The downside of using a single repository is that different projects may have different commit mailing
lists or different authentication and authorization requirements. Also, remember that Subversion uses
repository-global revision numbers. Some folks don't like the fact that even though no changes have
been made to their project lately, the youngest revision number for the repository keeps climbing because other projects are actively adding new revisions.
A middle-ground approach can be taken, too. For example, projects can be grouped by how well they relate to each other. You might have a few repositories with a handful of projects in each repository. That
way, projects that are likely to want to share data can do so easily, and as new revisions are added to the
repository, at least the developers know that those new revisions are at least remotely related to everyone who uses that repository.
After deciding how to organize your projects with respect to repositories, you'll probably want to think
about directory hierarchies in the repositories themselves. Because Subversion uses regular directory
copies for branching and tagging (see Chapter 4, Branching and Merging), the Subversion community
recommends that you choose a repository location for each project root—the “top-most” directory
which contains data related to that project—and then create three subdirectories beneath that root:
trunk, meaning the directory under which the main project development occurs; branches, which is
a directory in which to create various named branches of the main development line; tags, which is a
directory of branches that are created, and perhaps destroyed, but never changed.
For example, your repository might look like:
Note that it doesn't matter where in your repository each project root is. If you have only one project per
repository, the logical place to put each project root is at the root of that project's respective repository.
If you have multiple projects, you might want to arrange them in groups inside the repository, perhaps
putting projects with similar goals or shared code in the same subdirectory, or maybe just grouping them
alphabetically. Such an arrangment might look like:
Repository Administration
Lay out your repository in whatever way you see fit. Subversion does not expect or enforce a layout
schema—in its eyes, a directory is a directory is a directory. Ultimately, you should choose the repository arrangement that meets the needs of the people who work on the projects that live there.
Creating the Layout, and Importing Initial Data
After deciding how to arrange the projects in your repository, you'll probably want to actually populate
the repository with that layout and with initial project data. There are a couple of ways to do this in Subversion. You could use the svn mkdir command (see Chapter 9, Subversion Complete Reference) to create each directory in your skeletal repository layout, one-by-one. A quicker way to accomplish the same
task is to use the svn import command (see the section called “svn import”). By first creating the layout
in a temporary location on your drive, you can import the whole layout tree into the repository in a single commit:
$ mkdir tmpdir
$ cd tmpdir
$ mkdir projectA
$ mkdir projectA/trunk
$ mkdir projectA/branches
$ mkdir projectA/tags
$ mkdir projectB
$ mkdir projectB/trunk
$ mkdir projectB/branches
$ mkdir projectB/tags
$ svn import . file:///path/to/repos --message 'Initial repository layout'
Committed revision 1.
$ cd ..
$ rm -rf tmpdir
Once you have your skeletal layout in place, you can begin importing actual project data into your
repository, if any such data exists yet. Once again, there are several ways to do this. You could use the
svn import command. You could checkout a working copy from your new repository, move and arrange project data inside the working copy, and use the svn add and svn commit commands. But once
we start talking about such things, we're no longer discussing repository administration. If you aren't already familiar with the svn client program, see Chapter 3, Guided Tour.
Repository Administration
By now you should have a basic understanding of how to create, configure, and maintain Subversion
repositories. We've introduced you to the various tools that will assist you with this task. Throughout the
chapter, we've noted common administration pitfalls, and suggestions for avoiding them.
All that remains is for you to decide what exciting data to store in your repository, and finally, how to
make it available over a network. The next chapter is all about networking.
Chapter 6. Server Configuration
A Subversion repository can be accessed simultaneously by clients running on the same machine on
which the repository resides using the file:/// method. But the typical Subversion setup involves a
single server machine being accessed from clients on computers all over the office—or, perhaps, all over
the world.
This section describes how to get your Subversion repository exposed outside its host machine for use
by remote clients. We will cover Subversion's currently available server mechanisms, discussing the
configuration and use of each. After reading this section, you should be able to decide which networking
setup is right for your needs, and understand how to enable such a setup on your host computer.
Subversion was designed with an abstract network layer. This means that a repository can be programmatically accessed by any sort of server process, and the client "repository access" API allows programmers to write plugins that speak relevant network protocols. In theory, Subversion can sport an infinite
number of network implementations. In practice, there are only two servers at the time of writing.
Apache is an extremely popular webserver; using the mod_dav_svn module, Apache can access a
repository and make it available to clients via WebDAV/DeltaV protocol, which is an extension of
HTTP. In the other corner is svnserve: a small, standalone server program that speaks a custom protocol
with clients.
Note that Subversion, as an open-source project, does not officially endorse any server as "primary" or
"official". Neither network implementation is treated as a second-class citizen; each server has distinct
advantages and disadvantages. In fact, it's possible for different servers to run in parallel, each accessing
your repositories in its own way, and each without hindering the other (see the section called Support“ing Multiple Repository Access Methods”). Here's a brief overview and comparison of the two available Subversion servers— as an administrator, it's up to you to choose whatever works best for you and
your users.
Table 6.1. Network Server Comparison
Apache + mod_dav_svn
Authentication options
HTTP(S) basic auth, X.509 cer- CRAM-MD5 or SSH
tificates, LDAP, NTLM, or any
other mechanism available to
Apache httpd
User account options
private 'users' file
Authorization options
blanket read/write access, or per- blanket read/write access
directory access control
via optional SSL
partially usable by other Web- not interoperable
DAV clients
Web Viewing
limited built-in support, or via via 3rd-party
3rd-party tools such as ViewCVS ViewCVS
somewhat slower
somewhat faster
Initial setup
somewhat complex
fairly simple
private 'users' file, or existing
system (SSH) accounts
via optional SSH tunnel
Server Configuration
Network Model
This section is a general discussion of how a Subversion client and server interact with one another, regardless of the network implementation you're using. After reading, you'll have a good understanding of
how a server can behave and the different ways in which a client can be configured to respond.
Requests and Responses
The Subversion client spends most of its time managing working copies. When it needs information
from a repository, however, it makes a network request, and the server responds with an appropriate answer. The details of the network protocol are hidden from the user; the client attempts to access a URL,
and depending on the URL schema, a particular protocol is used to contact the server (see Repository
URLs). Users can run svn --version to see which URL schemas and protocols the client knows how to
When the server process receives a client request, it typically demands that the client identify itself. It issues an authentication challenge to the client, and the client responds by providing credentials back to
the server. Once authentication is complete, the server responds with the original information the client
asked for. Notice that this system is different from systems like CVS, where the client pre-emptively offers credentials ("logs in") to the server before ever making a request. In Subversion, the server "pulls"
credentials by challenging the client at the appropriate moment, rather than the client "pushing" them.
This makes certain operations more elegant. For example, if a server is configured to allow anyone in
the world to read a repository, then the server will never issue an authentication challenge when a client
attempts to svn checkout.
If the client's network request writes new data to the repository (e.g. svn commit), then a new revision
tree is created. If the client's request was authenticated, then the authenticated user's name is stored as
the value of the svn:author property on the new revision (see the section called “Unversioned Properties”). If the client was not authenticated (in other words, the server never issued an authentication
challenge), then the revision's svn:author property is empty. 19
Client Credentials Caching
Many servers are configured to require authentication on every request. This can become a big annoyance to users, who are forced to type their passwords over and over again.
Happily, the Subversion client has a remedy for this: a built-in system for caching authentication credentials on disk. By default, whenever the commandline client successfully authenticates itself to a server, it
saves the credentials in the user's private runtime configuration area— in ~/.subversion/auth/
on Unix-like systems or %APPDATA%/Subversion/auth/ on Windows. (The runtime area is covered in more detail in the section called “Runtime Configuration Area”.) Successful credentials are
cached on disk, keyed on a combination of hostname, port, and authentication realm.
When the client receives an authentication challenge, it first looks for the appropriate credentials in the
disk cache; if not present, or if the cached credentials fail to authenticate, then the client simply prompts
the user for the information.
The security-paranoid people may be thinking to themselves, "caching passwords on disk? That's terrible! You should never do that!" But please remain calm. First, the auth/ caching area is permission-protected so that only the user (owner) can read data from it, not the world at large. If that's still not safe
enough for you, you can disable credential caching. To disable caching for a single command, pass the -no-auth-cache option:
$ svn commit -F log_msg.txt --no-auth-cache
Authentication realm: <svn://> example realm
This problem is actually a FAQ, resulting from a misconfigured server setup.
Server Configuration
Username: joe
Password for 'joe':
Transmitting file data .
Committed revision 2324.
# password was not cached, so a second commit still prompts us
$ svn rm newfile
$ svn commit -F new_msg.txt
Authentication realm: <svn://> example realm
Username: joe
Or, if you want to disable credential caching permanently, you can edit your runtime config file
(located next to the auth/ directory). Simply set
store-auth-creds = no
... and no credentials will be cached on disk, ever.
Sometimes users will want to remove specific credentials from the disk cache. To do this, you need to
navigate into the auth/ area and manually delete the appropriate cache file. Credentials are cached in
individual files; if you look inside each file, you will see keys and values. The svn:realmstring
key describes the particular server realm that the file is associated with:
$ ls ~/.subversion/auth/svn.simple/
$ cat ~/.subversion/auth/svn.simple/5671adf2865e267db74f09ba6f872c28
K 8
V 3
K 8
V 4
K 15
V 45
<> Joe's repository
Once you have located the proper cache file, just delete it.
One last word about client authentication behavior: a bit of explanation about the --username and -password options is needed. Many client subcommands accept these options; however it is important to understand using these options does not automatically send credentials to the server. As discussed
earlier, the server "pulls" credentials from the client when it deems necessary; the client cannot "push"
them at will. If a username and/or password are passed as options, they will only be presented to the
server if the server requests them. 20 Typically, these options are used when:
Server Configuration
the user wants to authenticate as a different user than her system login name, or
a script wants to authenticate without using cached credentials.
Here is a final summary that describes how a Subversion client behaves when it receives an authentication challenge:
Check whether the user specified any credentials as commandline options, via --username and/
or --password. If not, or if these options fail to authenticate successfully, then
Look up the server's realm in the runtime auth/ area, to see if the user already has the appropriate
credentials cached. If not, or if the cached credentials fail to authenticate, then
Resort to prompting the user.
If the client successfully authenticates by any of the methods listed above, it will attempt to cache the
credentials on disk (unless the user has disabled this behavior, as mentioned earlier.)
svnserve, a custom server
The svnserve program is a lightweight server, capable of speaking to clients over TCP/IP using a custom, stateful protocol. Clients contact an svnserve server by using URLs that begin with the svn:// or
svn+ssh:// schema. This section will explain the different ways of running svnserve, how clients
authenticate themselves to the server, and how to configure appropriate access control to your repositories.
Invoking the Server
There a few different ways to invoke the svnserve program. If invoked with no options, you'll see nothing but a help message. However, if you're planning to have inetd launch the process, then you can pass
the -i (--inetd) option:
$ svnserve -i
( success ( 1 2 ( ANONYMOUS ) ( edit-pipeline ) ) )
When invoked with the --inetd option, svnserve attempts to speak with a Subversion client via stdin
and stdout using a custom protocol. This is the standard behavior for a program being run via inetd. The
IANA has reserved port 3690 for the Subversion protocol, so on a Unix-like system you can add lines to
/etc/services like these (if they don't already exist):
# Subversion
# Subversion
...and when a client connection comes into your server on port 3690, inetd will spawn an svnserve process to service it.
A second option is to run svnserve as a standalone "daemon" process. Use the -d option for this:
Again, a common mistake is to misconfigure a server so that it never issues an authentication challenge. When users pass -username and --password options to the client, they're surprised to see that they're never used, i.e. new revisions still appear to have been committed anonymously!
Server Configuration
$ svnserve -d
# svnserve is now running, listening on port 3690
When running svnserve in daemon mode, you can use the --listen-port= and
-listen-host= options to customize the exact port and hostname to "bind" to.
There's still a third way to invoke svnserve, and that's in "tunnel mode", with the -t option. This mode
assumes that a remote-service program such as RSH or SSH has successfully authenticated a user and is
now invoking a private svnserve process as that user. The svnserve program behaves normally
(communicating via stdin and stdout), and assumes that the traffic is being automatically redirected over
some sort of tunnel back to the client. When svnserve is invoked by a tunnel agent like this, be sure that
the authenticated user has full read and write access to the repository database files. (See Servers and
Permissions: A Word of Warning.) It's essentially the same as a local user accessing the repository via
file:/// URLs.
Servers and Permissions: A Word of Warning
First, remember that a Subversion repository is a collection of BerkeleyDB database files; any process
which accesses the repository directly needs to have proper read and write permissions on the entire
repository. If you're not careful, this can lead to a number of headaches. Be sure to read the section
called “Supporting Multiple Repository Access Methods”.
Secondly, when configuring svnserve, Apache httpd, or any other server process, keep in mind that you
might not want to launch the server process as the user root (or as any other user with unlimited permissions). Depending on the ownership and permissions of the repositories you're exporting, it's often
prudent to use a different—perhaps custom—user. For example, many administrators create a new user
named svn, grant that user exclusive ownership and rights to the exported Subversion repositories, and
only run their server processes as that user.
Once the svnserve program is running, it makes every repository on your system available to the network. A client needs to specify an absolute path in the repository URL. For example, if a repository is
located at /usr/local/repositories/project1, then a client would reach it via
svn:// . To increase security,
you can pass the -r option to svnserve, which restricts it to exporting only repositories below that path:
$ svnserve -d -r /usr/local/repositories
Using the -r option effectively modifies the location that the program treats as the root of the remote
filesystem space. Clients then use URLs that have that path portion removed from them, leaving much
shorter (and much less revealing) URLs:
$ svn checkout svn://
Built-in authentication and authorization
When a client connects to an svnserve process, the following things happen:
The client selects a specific repository.
Server Configuration
The server processes the repository's conf/svnserve.conf file, and begins to enforce any authentication and authorization policies defined therein.
Depending on the situation and authorization policies,
the client may be allowed to make requests anonymously, without ever receiving an authentication challenge, OR
the client may be challenged for authentication at any time, OR
if operating in "tunnel mode", the client will declare itself to be already externally authenticated.
At the time of writing, the server only knows how to send a CRAM-MD5 21 authentication challenge. In
essence, the server sends a bit of data to the client. The client uses its password to encrypt the data with
the MD5 hash algorithm, and sends it back. The server performs the same computation with the stored
password to verify that the result is identical. At no point does the actual password travel over the network.
It's also possible, of course, for the client to be externally authenticated via a tunnel agent, such as SSH.
In that case, the server simply examines the user it's running as, and uses it as the authenticated username.
As you've already guessed, a repository's svnserve.conf file is the central mechanism for controlling authentication and authorization policies. The file has the same format as other configuration files
(see the section called “Runtime Configuration Area”): section names are marked by [square
brackets], comments begin with "#" characters, and each section contains specific variables that can
be set (variable = value). Let's walk through this file and learn how to use them.
Create a 'users' file and realm
For now, the [general] section of the svnserve.conf has all the variables you need. Begin by
defining a file which contains usernames and passwords, and an authentication realm:
password-db = userfile
realm = example realm
The realm is a name that you define. It tells clients which sort of "authentication namespace" they're
connecting to; the Subversion client displays it in the authentication prompt, and uses it as a key (along
with the server's hostname and port) for caching credentials on disk (see the section called “Client Credentials Caching”.) The password-db variable points to a separate file that contains a list of usernames and passwords, using the same familiar format. For example:
harry = foopassword
sally = barpassword
The value of password-db can be an absolute or relative path to the users file. For many admins, it's
easy to keep the file right in the conf/ area of the repository, alongside svnserve.conf. On the
other hand, it's possible you may want to have two or more repositories share the same users file; in that
case, the file should probably live in a more public place. The repositories sharing the users file should
also be configured to have the same realm, since the list of users essentially defines an authentication
See RFC 2195.
Server Configuration
realm. Wherever the file lives, be sure to set the file's read and write permissions appropriately. If you
know which user(s) svnserve will run as, restrict read access to the user file as necessary.
Set access controls
There are two more variables to set in the svnserve.conf file: they determine what unauthenticated
(anonymous) and authenticated users are allowed to do. The variables anon-access and authaccess can be set to the values none, read, or write. "none" restricts all access of any kind,
"read" allows read-only access to the repository, and "write" allows complete read/write access to
the repository. For example:
password-db = userfile
realm = example realm
# anonymous users can only read the repository
anon-access = read
# authenticated users can both read and write
auth-access = write
The example settings are, in fact, the default values of the variables, should you forget to define them. If
you want to be even more conservative, you can block anonymous access completely:
password-db = userfile
realm = example realm
# anonymous users aren't allowed
anon-access = none
# authenticated users can both read and write
auth-access = write
Notice that svnserve only understands "blanket" access control. A user either has universal read/write
access, universal read access, or no access. There is no detailed control over access to specific paths
within the repository. For many projects and sites, this level of access control is more than adequate.
However, if you need per-directory access control, you'll need to use Apache instead of svnserve as
your server process.
SSH authentication and authorization
svnserve's built-in authentication can be very handy, because it avoids the need to create real system accounts. On the other hand, some administrators already have well-established SSH authentication frameworks in place. In these situations, all of the project's users already have system accounts and the ability
to "SSH into" the server machine.
It's easy to use SSH in conjunction with svnserve. The client simply uses the svn+ssh:// URL
schema to connect:
$ whoami
$ svn list svn+ssh://'s password: *****
Server Configuration
What's happening here is that the Subversion client is invoking a local ssh process, connecting to, authenticating as user 'harry', then spawning a private svnserve process on the
remote machine, running as user 'harry'. The svnserve command is being invoked in tunnel mode (-t)
and all network protocol is being "tunneled" over the encrypted connection by ssh, the tunnel-agent.
svnserve is aware that it's running as user 'harry', and if the client performs a commit, the authenticated
username will be attributed as the author of the new revision.
When running over a tunnel, authorization is primarily controlled by operating system permissions to
the repository's database files; it's very much the same as if harry were accessing the repository directly
via a file:/// URL. If multiple system users are going to be accessing the repository directly, you
may want to place them into a common group, and you'll need to be careful about umasks. (Be sure to
read the section called “Supporting Multiple Repository Access Methods”.) But even in the case of tunneling, the svnserve.conf file can still be used to block access, by simply setting auth-access
= read or auth-access = none.
You'd think that the story of SSH tunneling would end here, but it doesn't. Subversion allows you to create custom tunnel behaviors in your run-time config file (see the section called “Runtime Configuration Area”.) For example, suppose you want to use RSH instead of SSH. In the [tunnels] section of
your config file, simply define it like this:
rsh = rsh
And now, you can use this new tunnel definition by using a URL schema that matches the name of your
new variable: svn+rsh://host/path. When using the new URL schema, the Subversion client
will actually be running the command rsh host svnserve -t behind the scenes. If you include a username
in the URL (for example, svn+rsh://username@host/path) the client will also include that in
its command (rsh username@host svnserve -t.) But you can define new tunneling schemes to be much
more clever than that:
joessh = $JOESSH /opt/alternate/ssh -p 29934
This example demonstrates a couple of things. First, it shows how to make the Subversion client launch
a very specific tunneling binary (the one located at /opt/alternate/ssh) with specific options. In
this case, accessing a svn+joessh:// URL would invoke the particular SSH binary with -p 29934
as arguments— useful if you want the tunnel program to connect to a non-standard port. Second, it
shows how to define a custom environment variable that can override the name of the tunneling program. If we were to set the JOESSH environment variable, its value would override the entire value of
the tunnel variable; $JOESSH would be executed instead of /opt/alternate/ssh -p 29934.
httpd, the Apache HTTP server
The Apache HTTP Server is a "heavy duty" network server that Subversion can leverage. Via a custom
module, httpd makes Subversion repositories available to clients via the WebDAV/DeltaV protocol,
which is an extension to HTTP 1.1 (see for more information.) This
protocol takes the ubiquitous HTTP protocol that is core of the World Wide Web, and adds
writing—specifically, versioned writing—capabilities. The result is a standardized, robust system that is
conveniently packaged as part of the Apache 2.0 software, is supported by numerous operating systems
Server Configuration
and third-party products, and which doesn't require network administrators to open up yet another custom port. 22 While an Apache-Subversion server has more features than svnserve, it's also a bit more
difficult to set up. With flexibility often comes more complexity.
Much of the following discussion includes references to Apache configuration directives. While some
examples are given of the use of these directives, describing them in full is outside the scope of this
chapter. The Apache team maintains excellent documentation, publicly available on their website at For example, a general reference for the configuration directives is
located at
Also, as you make changes to your Apache setup, it is likely that somewhere along the way a mistake
will be made. If you are not already familiar with Apache's logging subsystem, you should become
aware of it. In your httpd.conf file are directives that specify the on-disk locations of the access and
error logs generated by Apache (the CustomLog and ErrorLog directives, respectively). Subversion's mod_dav_svn uses Apache's error logging interface as well. You can always browse the contents
of those files for information that might reveal the source of a problem that is not clearly noticeable otherwise.
Why Apache 2?
If you're a system administrator, it's very likely that you're already running the Apache web server and
have some prior experience with it. At the time of writing, Apache 1.3 is by far the most popular version
of Apache. The world has been somewhat slow to upgrade to the Apache 2.X series for various reasons:
some people fear change, especially changing something as critical as a web server. Other people depend on plug-in modules that only work against the Apache 1.3 API, and are waiting for a 2.X port.
Whatever the reason, many people begin to worry when they first discover that Subversion's Apache
module is written specifically for the Apache 2 API.
The proper response to this problem is: don't worry about it. It's easy to run Apache 1.3 and Apache 2
side-by-side; simply install them to separate places, and use Apache 2 as a dedicated Subversion server
that runs on a port other than 80. Clients can access the repository by placing the port number into the
$ svn checkout
To network your repository over HTTP, you basically need four components, available in two packages.
You'll need Apache httpd 2.0, the mod_dav DAV module that comes with it, Subversion, and the
mod_dav_svn filesystem provider module distributed with Subversion. Once you have all of those components, the process of networking your repository is as simple as:
getting httpd 2.0 up and running with the mod_dav module,
installing the mod_dav_svn plugin to mod_dav, which uses Subversion's libraries to access the
repository, and
configuring your httpd.conf file to export (or expose) the repository.
You can accomplish the first two items either by compiling httpd and Subversion from source code, or
by installing pre-built binary packages of them on your system. For the most up-to-date information on
They really hate doing that.
Server Configuration
how to compile Subversion for use with the Apache HTTP Server, as well as how to compile and configure Apache itself for this purpose, see the INSTALL file in the top level of the Subversion source
code tree.
Basic Apache Configuration
Once you have all the necessary components installed on your system, all that remains is the configuration of Apache via its httpd.conf file. Instruct Apache to load the mod_dav_svn module using the
LoadModule directive. This directive must precede any other Subversion-related configuration items.
If your Apache was installed using the default layout, your mod_dav_svn module should have been installed in the modules subdirectory of the Apache install location (often /usr/local/apache2).
The LoadModule directive has a simple syntax, mapping a named module to the location of a shared
library on disk:
LoadModule dav_svn_module
Note that if mod_dav was compiled as a shared object (instead of statically linked directly to the httpd
binary), you'll need a similar LoadModule statement for it, too.
At a later location in your configuration file, you now need to tell Apache where you keep your Subversion repository (or repositories). The Location directive has an XML-like notation, starting with an
opening tag, and ending with a closing tag, with various other configuration directives in the middle.
The purpose of the Location directive is to instruct Apache to do something special when handling
requests that are directed at a given URL or one of its children. In the case of Subversion, you want
Apache to simply hand off support for URLs that point at versioned resources to the DAV layer. You
can instruct Apache to delegate the handling of all URLs whose path portions (the part of the URL that
follows the server's name and the optional port number) begin with /repos/ to a DAV provider whose
repository is located at /absolute/path/to/repository using the following httpd.conf
<Location /repos>
DAV svn
SVNPath /absolute/path/to/repository
If you plan to support multiple Subversion repositories that will reside in the same parent directory on
your local disk, you can use an alternative directive, the SVNParentPath directive, to indicate that
common parent directory. For example, if you know you will be creating multiple Subversion repositories in a directory /usr/local/svn that would be accessed via URLs like,, and so
on, you could use the httpd.conf configuration syntax in the following example:
<Location /svn>
DAV svn
# any "/svn/foo" URL will map to a repository /usr/local/svn/foo
SVNParentPath /usr/local/svn
Using the previous syntax, Apache will delegate the handling of all URLs whose path portions begin
with /svn/ to the Subversion DAV provider, which will then assume that any items in the directory
specified by the SVNParentPath directive are actually Subversion repositories. This is a particularly
convenient syntax in that, unlike the use of the SVNPath directive, you don't have to restart Apache in
order to create and network new repositories.
Server Configuration
Be sure that when you define your new Location, it doesn't overlap with other exported Locations.
For example, if your main DocumentRoot to /www, do not export a Subversion repository in Lo<cation /www/repos>. If a request comes in for the URI /www/repos/foo.c, Apache won't
know whether to look for a file repos/foo.c in the DocumentRoot, or whether to delegate
mod_dav_svn to return foo.c from the Subversion repository.
Server Names and the COPY Request
Subversion makes use of the COPY request type to perform server-side copies of files and directories. As
part of the sanity checking done by the Apache modules, the source of the copy is expected to be located
on the same machine as the destination of the copy. To satisfy this requirement, you might need to tell
mod_dav the name you use as the hostname of your server. Generally, you can use the ServerName
directive in httpd.conf to accomplish this.
If you are using Apache's virtual hosting support via the NameVirtualHost directive, you may need
to use the ServerAlias directive to specify additional names that your server is known by. Again, refer to the Apache documentation for full details.
At this stage, you should strongly consider the question of permissions. If you've been running Apache
for some time now as your regular web server, you probably already have a collection of content—web
pages, scripts and such. These items have already been configured with a set of permissions that allows
them to work with Apache, or more appropriately, that allows Apache to work with those files. Apache,
when used as a Subversion server, will also need the correct permissions to read and write to your Subversion repository. (See Servers and Permissions: A Word of Warning.)
You will need to determine a permission system setup that satisfies Subversion's requirements without
messing up any previously existing web page or script installations. This might mean changing the permissions on your Subversion repository to match those in use by other things that Apache serves for
you, or it could mean using the User and Group directives in httpd.conf to specify that Apache
should run as the user and group that owns your Subversion repository. There is no single correct way to
set up your permissions, and each administrator will have different reasons for doing things a certain
way. Just be aware that permission-related problems are perhaps the most common oversight when configuring a Subversion repository for use with Apache.
Authentication Options
At this point, if you configured httpd.conf to contain something like
<Location /svn>
DAV svn
SVNParentPath /usr/local/svn
...then your repository is "anonymously" accessible to the world. Until you configure some authentication and authorization policies, the Subversion repositories you make available via the Location directive will be generally accessible to everyone. In other words,
anyone can use their Subversion client to checkout a working copy of a repository URL (or any of its
Server Configuration
anyone can interactively browse the repository's latest revision simply by pointing their web browser
to the repository URL, and
anyone can commit to the repository.
Basic HTTP Authentication
The easiest way to authenticate an client is via the HTTP Basic authentication mechanism, which simply
uses a username and password to verify that a user is who she says she is. Apache provides an htpasswd
utility for managing the list of acceptable usernames and passwords, those to whom you wish to grant
special access to your Subversion repository. Let's grant commit access to Sally and Harry. First, we
need to add them to the password file.
$ ### First time: use -c to create the file
$ ### Use -m to use MD5 encryption of the password, which is more secure
$ htpasswd -cm /etc/svn-auth-file harry
New password: *****
Re-type new password: *****
Adding password for user harry
$ htpasswd /etc/svn-auth-file -m sally
New password: *******
Re-type new password: *******
Adding password for user sally
Next, you need to add some more httpd.conf directives inside your Location block to tell Apache
what to do with your new password file. The AuthType directive specifies the type of authentication
system to use. In this case, we want to specify the Basic authentication system. AuthName is an arbitrary name that you give for the authentication domain. Most browsers will display this name in the popup dialog box when the browser is querying the user for his name and password. Finally, use the AuthUserFile directive to specify the location of the password file you created using htpasswd.
After adding these three directives, your <Location> block should look something like this:
<Location /svn>
DAV svn
SVNParentPath /usr/local/svn
AuthType Basic
AuthName "Subversion repository"
AuthUserFile /etc/svn-auth-file
This <Location> block is not yet complete, and will not do anything useful. It's merely telling
Apache that whenever authorization is required, Apache should harvest a username and password from
the Subversion client. What's missing here, however, are directives that tell Apache which sorts of client
requests require authorization. Wherever authorization is required, Apache will demand authentication
as well. The simplest thing to do is protect all requests. Adding Require valid-user tells Apache
that all requests require an authenticated user:
<Location /svn>
DAV svn
SVNParentPath /usr/local/svn
AuthType Basic
AuthName "Subversion repository"
AuthUserFile /etc/svn-auth-file
Server Configuration
Require valid-user
Be sure to read the next section (the section called “Authorization Options”) for more detail on the Require directive and other ways to set authorization policies.
One word of warning: HTTP Basic Auth passwords pass in very nearly plain-text over the network, and
thus are extremely insecure. If you're worried about password snooping, it may be best to use some sort
of SSL encryption, so that clients authenticate via https:// instead of http://; at a bare minimum,
you can configure Apache to use a self-signed server certificate. 23 Consult Apache's documentation
(and OpenSSL documentation) about how to do that.
SSL Certificate Management
Businesses that need to expose their repositories for access outside the company firewall should be conscious of the possibility that unauthorized parties could be “sniffing” their network traffic. SSL makes
that kind of unwanted attention less likely to result in sensitive data leaks.
If a Subversion client is compiled to use OpenSSL, then it gains the ability to speak to an Apache server
via https:// URLs. The Neon library used by the Subversion client is not only able to verify server
certificates, but can also supply client certificates when challenged. When the client and server have exchanged SSL certificates and successfully authenticated one another, all further communication is encrypted via a session key.
It's beyond the scope of this book to describe how to generate client and server certificates, and how to
configure Apache to use them. Many other books, including Apache's own documentation, describe this
task. But what can be covered here is how to manage server and client certificates from an ordinary Subversion client.
When speaking to Apache via https://, a Subversion client can receive two different types of information:
a server certificate
a demand for a client certificate
If the client receives a server certificate, it needs to verify that it trusts the certificate: is the server really
who it claims to be? The OpenSSL library does this by examining the signer of the server certificate, or
certifying authority (CA). If OpenSSL is unable to automatically trust the CA, or if some other problem
occurs (such as an expired certificate or hostname mismatch), the Subversion commandline client will
ask you whether you want to trust the server certificate anyway:
$ svn list
Error validating server certificate for '':
- The certificate is not issued by a trusted authority. Use the
fingerprint to validate the certificate manually!
Certificate information:
- Hostname:
- Valid: from Jan 30 19:23:56 2004 GMT until Jan 30 19:23:56 2006 GMT
- Issuer: CA,, Sometown, California, US
- Fingerprint: 7d:e1:a9:34:33:39:ba:6a:e9:a5:c4:22:98:7b:76:5c:92:a0:9c:7b
(R)eject, accept (t)emporarily or accept (p)ermanently?
While self-signed server certificates are still vulnerable to a “man in the middle” attack, such an attack is still much more difficult for a casual observer to pull off, compared to sniffing unprotected passwords.
Server Configuration
This dialogue should look familiar; it's essentially the same question you've probably seen coming from
your web browser (which is just another HTTP client like Subversion!). If you choose the (p)ermanent
option, the server certificate will be cached in your private run-time auth/ area in just the same way
your username and password are cached (see the section called “Client Credentials Caching”.) If cached,
Subversion will automatically remember to trust this certificate in future negotiations.
Your run-time servers file also gives you the ability to make your Subversion client automatically
trust specific CAs, either globally or on a per-host basis. Simply set the ssl-authority-files
variable to a semicolon-separated list of PEM-encoded CA certificates:
ssl-authority-files = /path/to/CAcert1.pem;/path/to/CAcert2.pem
Many OpenSSL installations also have a pre-defined set of “default” CAs that are nearly universally
trusted. To make the Subversion client automatically trust these standard authorities, set the ssltrust-default-ca variable to true.
When talking to Apache, a Subversion client might also receive a challenge for a client certificate.
Apache is asking the client to identify itself: is the client really who it says it is? If all goes correctly, the
Subversion client sends back a private certificate signed by a CA that Apache trusts. A client certificate
is usually stored on disk in encrypted format, protected by a local password. When Subversion receives
this challenge, it will ask you for both a path to the certificate and the password which protects it:
$ svn list
Authentication realm:
Client certificate filename: /path/to/my/cert.p12
Passphrase for '/path/to/my/cert.p12': ********
Notice that the client certificate is a “p12” file. To use a client certificate with Subversion, it must be in
PKCS#12 format, which is a portable standard. Most web browsers are already able to import and export
certificates in that format. Another option is to use the OpenSSL commandline tools to convert existing
certificates into PKCS#12.
Again, the runtime servers file allows you to automate this challenge on a per-host basis. Either or
both pieces of information can be described in runtime variables:
examplehost =
ssl-client-cert-file = /path/to/my/cert.p12
ssl-client-cert-password = somepassword
Once you've set the ssl-client-cert-file and ssl-client-cert-password variables, the
Subversion client can automatically respond to a client certificate challenge without prompting you. 24
Authorization Options
Blanket Access Control
More security-conscious folk might not want to store the client certificate password in the runtime servers file.
Server Configuration
The simplest form of access control is to authorize certain users for either read-only access to a repository, or read/write access to a repository.
You can restrict access on all repository operations by adding the Require valid-user directive to
your <Location> block. Using our previous example, this would mean that only clients that claimed
to be either harry or sally, and which provided the correct password for their respective username,
would be allowed to do anything with the Subversion repository:
<Location /svn>
DAV svn
SVNParentPath /usr/local/svn
# how to authenticate a user
AuthType Basic
AuthName "Subversion repository"
AuthUserFile /path/to/users/file
# only authenticated users may access the repository
Require valid-user
Sometimes you don't need to run such a tight ship. For example, Subversion's own source code repository at allows anyone in the world to perform read-only
repository tasks (like checking out working copies and browsing the repository with a web browser), but
restricts all write operations to authenticated users. To do this type of selective restriction, you can use
the Limit and LimitExcept configuration directives. Like the Location directive, these blocks
have starting and ending tags, and you would nest them inside your <Location> block.
The parameters present on the Limit and LimitExcept directives are HTTP request types that are
affected by that block. For example, if you wanted to disallow all access to your repository except the
currently supported read-only operations, you would use the LimitExcept directive, passing the GET,
PROPFIND, OPTIONS, and REPORT request type parameters. Then the previously mentioned Require valid-user directive would be placed inside the <LimitExcept> block instead of just
inside the <Location> block.
<Location /svn>
DAV svn
SVNParentPath /usr/local/svn
# how to authenticate a user
AuthType Basic
AuthName "Subversion repository"
AuthUserFile /path/to/users/file
# For any operations other than these, require an authenticated user.
Require valid-user
These are only a few simple examples. For more in-depth information about Apache access control and
the Require directive,, take a look at the Security section of the Apache documentation's tutorials
collection at
Per-Directory Access Control
It's possible to set up finer-grained permissions using a second Apache httpd module, mod_authz_svn.
Server Configuration
This module grabs the various opaque URLs passing from client to server, asks mod_dav_svn to decode
them, and then possibly vetoes requests based on access policies defined in a configuration file.
If you've built Subversion from source code, mod_authz_svn is automatically built and installed alongside mod_dav_svn. Many binary distributions install it automatically as well. To verify that it's installed
correctly, make sure it comes right after mod_dav_svn's LoadModule directive in httpd.conf:
LoadModule dav_svn_module
LoadModule authz_svn_module
To activate this module, you need to configure your Location block to use the AuthzSVNAccessFile directive, which specifies a file containing the permissions policy for paths within your repositories. (In a moment, we'll discuss the format of that file.)
Apache is flexible, so you have the option to configure your block in one of three general patterns. To
begin, choose one of these basic configuration patterns. (The examples below are very simple; look at
Apache's own documentation for much more detail on Apache authentication and authorization options.)
The simplest block is to allow open access to everyone. In this scenario, Apache never sends authentication challenges, so all users are treated as “anonymous”.
Example 6.1. A sample configuration for anonymous access.
<Location /repos>
DAV svn
SVNParentPath /usr/local/svn
# our access control policy
AuthzSVNAccessFile /path/to/access/file
On the opposite end of the paranoia scale, you can configure your block to demand authentication from
everyone. All clients must supply credentials to identify themselves. Your block unconditionally requires authentication via the Require valid-user directive, and defines a means to authenticate.
Example 6.2. A sample configuration for authenticated access.
<Location /repos>
DAV svn
SVNParentPath /usr/local/svn
# our access control policy
AuthzSVNAccessFile /path/to/access/file
# only authenticated users may access the repository
Require valid-user
# how to authenticate a user
AuthType Basic
AuthName "Subversion repository"
AuthUserFile /path/to/users/file
Server Configuration
A third very popular pattern is to allow a combination of authenticated and anonymous access. For example, many administrators want to allow anonymous users to read certain repository directories, but
want only authenticated users to read (or write) more sensitive areas. In this setup, all users start out accessing the repository anonymously. If your access control policy demands a real username at any point,
Apache will demand authentication from the client. To do this, you use both the Satisfy Any and
Require valid-user directives together.
Example 6.3. A sample configuration for mixed authenticated/anonymous access.
<Location /repos>
DAV svn
SVNParentPath /usr/local/svn
# our access control policy
AuthzSVNAccessFile /path/to/access/file
# try anonymous access first, resort to real
# authentication if necessary.
Sasisfy Any
Require valid-user
# how to authenticate a user
AuthType Basic
AuthName "Subversion repository"
AuthUserFile /path/to/users/file
Once your basic Location block is configured, you can create an access file and define some authorization rules in it.
The syntax of the access file is the same familiar one used by svnserve.conf and the runtime configuration files. Lines that start with hash (#)) are ignored. In its simplest form, each “section” names a repository and path within it, and the authenticated usernames are the “variables” within each section. The
value of each variable describes the user's level of access to the repository path: either r (read-only) or
rw (read-write). If the user is not mentioned at all, no access is allowed.
To be more specific: the value of the section-names are either of the form [repos-name:path] or
the form [path]. If you're using the SVNParentPath directive, then it's important to specify the
repository names in your sections. If you omit them, then a section like [/some/dir] will match the
path /some/dir in every repository. If you're using the SVNPath directive, however, then it's fine to
only define paths in your sections—after all, there's only one repository.
harry = rw
sally = r
In this first example, user harry has full read and write access on the /branches/calc/bug-142
directory in the calc repository, but user sally has read-only access. Any other users are blocked from
accessing this directory.
Server Configuration
Of course, permissions “inherit” from parent to child directory. That means that we can specify a subdirectory with a different access policy for sally:
harry = rw
sally = r
# give sally write access only to the 'testing' subdir
sally = rw
Now sally can write to the testing subdirectory of the branch, but can still only read other parts.
Harry, meanwhile, continues to have complete read-write access to the whole branch.
It's also possible to explicitly deny permission to someone via inheritance rules, by setting the username
variable to nothing:
harry = rw
sally = r
harry =
In this example, harry has read-write access to the entire bug-142 tree, but has absolutely no access at
all to the secret subdirectory within it.
By default, nobody has any access to the repository at all. That means that if you're starting with an
empty file, you'll probably want to give at least read permission to all users at the root of the repository.
You can do this by using the asterisk variable (*), which means “all users”:
* = r
This is a common setup; notice that there's no repository name mentioned in the section name. This
makes all repositories world readable to all users, whether you're using SVNPath or
SVNParentPath. Once all users have read-access to the repositor(ies), you can give explicit rw permission to certain users on specific subdirectories within specific repositories.
The asterisk variable (*) is also worth special mention here: it's the only pattern which matches an
anonymous user. If you've configured your Location block to allow a mixture of anonymous and authenticated access, all users start out accessing Apache anonymously. mod_authz_svn looks for a *
value defined for the path being accessed; if it can't find one, then Apache demands real authentication
from the client.
The access file also allows you to define whole groups of users, much like the Unix /etc/group file:
calc-developers = harry, sally, joe
paint-developers = frank, sally, jane
everyone = harry, sally, joe, frank, sally, jane
Groups can be granted access control just like users. Distinguish them with a @ prefix:
Server Configuration
@calc-developers = rw
@paint-developers = rw
jane = r
...and that's pretty much all there is to it.
Extra Goodies
Repository Browsing
One of the most useful benefits of an Apache/WebDAV configuration for your Subversion repository is
that the youngest revisions of your versioned files and directories are immediately available for viewing
via a regular web browser. Since Subversion uses URLs to identify versioned resources, those URLs
used for HTTP-based repository access can be typed directly into a Web browser. Your browser will issue a GET request for that URL, and based on whether that URL represents a versioned directory or file,
mod_dav_svn will respond with a directory listing or with file contents.
Since the URLs do not contain any information about which version of the resource you wish to see,
mod_dav_svn will always answer with the youngest version. This functionality has the wonderful sideeffect that you can pass around Subversion URLs to your peers as references to documents, and those
URLs will always point at the latest manifestation of that document. Of course, you can even use the
URLs as hyperlinks from other web sites, too.
You generally will get more use out of URLs to versioned files—after all, that's where the interesting
content tends to lie. But you might have occasion to browse a Subversion directory listing, where you'll
quickly note that the generated HTML used to display that listing is very basic, and certainly not intended to be aesthetically pleasing (or even interesting). To enable customization of these directory displays, Subversion provides an XML index feature. A single SVNIndexXSLT directive in your repository's Location block of httpd.conf will instruct mod_dav_svn to generate XML output when
displaying a directory listing, and to reference the XSLT stylesheet of your choice:
<Location /svn>
DAV svn
SVNParentPath /usr/local/svn
SVNIndexXSLT "/svnindex.xsl"
Using the SVNIndexXSLT directive and a creative XSLT stylesheet, you can make your directory listings match the color schemes and imagery used in other parts of your website. Or, if you'd prefer, you
can use the sample stylesheets provided in the Subversion source distribution's tools/xslt/ directory. Keep in mind that the path provided to the SVNIndexXSLT directory is actually a URL
path—browsers need to be able to read your stylesheets in order to make use of them!
Can I view older revisions?
With an ordinary web browser? In one word: nope. At least, not with mod_dav_svn as your only tool.
Your web browser only speaks ordinary HTTP. That means it only knows how to GET public URLs,
which represent the latest versions of files and directories. According to the WebDAV/DeltaV spec,
each server defines a private URL syntax for older versions of resources, and that syntax is opaque to
Server Configuration
clients. To find an older version of a file, a client must follow a specific procedure to “discover” the
proper URL; the procedure involves issuing a series of WebDAV PROPFIND requests and understanding DeltaV concepts. This is something your web browser simply can't do.
So to answer the question, one obvious way to see older revisions of files and directories is by passing
the --revision argument to the svn list and svn cat commands. To browse old revisions with your
web browser, however, you can use third-party software. A good example of this is ViewCVS
( ViewCVS was originally written to display CVS
repositories through the web, and the latest bleeding-edge versions (at the time of writing) are able to
understand Subversion repositories as well.
Other Features
Several of the features already provided by Apache in its role as a robust Web server can be leveraged
for increased functionality or security in Subversion as well. Subversion communicates with Apache using Neon, which is a generic HTTP/WebDAV library with support for such mechanisms as SSL (the Secure Socket Layer, discussed earlier) and Deflate compression (the same algorithm used by the gzip and
PKZIP programs to “shrink” files into smaller chunks of data). You need only to compile support for
the features you desire into Subversion and Apache, and properly configure the programs to use those
Deflate compression places a small burden on the client and server to compress and decompress network
transmissions as a way to minimize the size of the actual transmission. In cases where network bandwidth is in short supply, this kind of compression can greatly increase the speed at which communications between server and client can be sent. In extreme cases, this minimized network transmission
could be the difference between an operation timing out or completing successfully.
Less interesting, but equally useful, are other features of the Apache and Subversion relationship, such
as the ability to specify a custom port (instead of the default HTTP port 80) or a virtual domain name by
which the Subversion repository should be accessed, or the ability to access the repository through a
proxy. These things are all supported by Neon, so Subversion gets that support for free.
Finally, because mod_dav_svn is speaking a semi-complete dialect of WebDAV/DeltaV, it's possible to
access the repository via third-party DAV clients. Most modern operating systems (Win32, OS X, and
Linux) have the built-in ability to mount a DAV server as a standard network "share". This is a complicated topic; for details, read Appendix C, WebDAV and Autoversioning.
Supporting Multiple Repository Access Methods
You've seen how a repository can be accessed in many different ways. But is it possible—or safe—for
your repository to be accessed by multiple methods simultaneously? The answer is yes, provided you
use a bit of foresight.
At any given time, these processes may require read and/or write access to your repository:
regular system users using a Subversion client (as themselves) to access the repository directly via
file:/// URLs;
regular system users connecting to SSH-spawned private svnserve processes (running as themselves) which access the repository;
an svnserve process—either a daemon or one launched by inetd—running as a particular fixed user;
Server Configuration
an Apache httpd process, running as a particular fixed user.
The most common problem administrators run into is repository ownership and permissions. Does every
process (or user) in the previous list have the rights to read and write the Berkeley DB files? Assuming
you have a Unix-like operating system, a straightforward approach might be to place every potential
repository user into a new svn group, and make the repository wholly owned by that group. But even
that's not enough, because a process may write to the database files using an unfriendly umask—one that
prevents access by other users.
So the next step beyond setting up a common group for repository users is to force every repository-accessing process to use a sane umask. For users accessing the repository directly, you can make the svn
program into a wrapper script that first sets umask 002 and then runs the real svn client program. You
can write a similar wrapper script for the svnserve program, and add a umask 002 command to
Apache's own startup script, apachectl. For example:
$ cat /usr/local/bin/svn
umask 002
/usr/local/subversion/bin/svn "$@"
Once you've jumped through these hoops, your repository should be accessible by all the necessary processes. It may seem a bit messy and complicated, but the problems of having multiple users sharing
write-access to common files are classic ones that are not often elegantly solved.
Fortunately, most repository administrators will never need to have such a complex configuration. Users
who wish to access repositories that live on the same machine are not limited to using file:// access
URLs—they can typically contact the Apache HTTP server or svnserve using localhost for the
server name in their http:// or svn:// URLs. And to maintain multiple server processes for your
Subversion repositories is likely to be more of a headache than necessary. We recommend you choose
the server that best meets your needs and stick with it!
Chapter 7. Advanced Topics
If you've been reading this book chapter by chapter, from start to finish, you should by now have acquired enough knowledge to use the Subversion client to perform the most common version control operations. You understand how to checkout a working copy from a Subversion repository. You are comfortable with submitting and receiving changes using the svn commit and svn update functions. You've
probably even developed a reflex which causes you to run the svn status command almost unconsciously. For all intents and purposes, you are ready to use Subversion in a typical environment.
But the Subversion feature set doesn't stop at "common version control operations".
This chapter highlights some of Subversion's features that aren't quite so regularly used. In it, we will
discuss Subversion's property (or “metadata”) support, and how to modify Subversion's default behaviors by tweaking its run-time configuration area. We will describe how you can use externals definitions
to instruct Subversion to pull data from multiple repositories. We'll cover in detail some of the additional
client- and server-side tools that are part of the Subversion distribution.
Before reading this chapter, you should be familiar with the basic file and directory versioning capabilities of Subversion. If you haven't already read about those, or if you need a refresher, we recommend
that you check out Chapter 2, Basic Concepts and Chapter 3, Guided Tour. Once you've mastered the
basics and consumed this chapter, you'll be a Subversion power-user—or we'll refund your money! 25
Runtime Configuration Area
Subversion provides many optional behaviors that can be controlled by the user. Many of these options
are of the kind that a user would wish to apply to all Subversion operations. So, rather than forcing users
to remember command-line arguments for specifying these options, and to use them for each and every
operation they perform, Subversion uses configuration files, segregated into a Subversion configuration
The Subversion configuration area is a two-tiered hierarchy of option names and their values. Usually,
this boils down to a special directory that contains configuration files (the first tier), which are just text
files in standard INI format (with “sections” providing the second tier). These files can be easily edited
using your favorite text editor (such as Emacs or vi), and contain directives read by the client to determine which of several optional behaviors the user prefers.
Configuration Area Layout
The first time that the svn command-line client is executed, it creates a per-user configuration area. On
Unix-like systems, this area appears as a directory named .subversion in the user's home directory.
On Win32 systems, Subversion creates a folder named Subversion, typically inside the Application Data area of the user's profile directory. However, on this platform the exact location differs
from system to system, and is dictated by the Windows registry. 26 We will refer to the per-user configuration area using its Unix name, .subversion.
In addition to the per-user configuration area, Subversion also recognizes the existence of a system-wide
configuration area. This gives system administrators the ability to establish defaults for all users on a
given machine. Note that the system-wide configuration area does not alone dictate mandatory
policy—the settings in the per-user configuration area override those in the system-wide one, and command-line arguments supplied to the svn program have the final word on behavior. On Unix-like
platforms, the system-wide configuration area is expected to be the /etc/subversion directory; on
Windows machines, it again looks for a Subversion directory inside the common Application Data
This offer applies only to those who, like most folks, pay nothing for Subversion.
The APPDATA environment variable points to the Application Data area, so you can always refer to this folder as
Advanced Topics
location (again, as specified by the Windows Registry). Unlike the per-user case, the svn program does
not attempt to create the system-wide configuration area.
The configuration area currently contains three files—two configuration files (config and servers),
and a README.txt file which describes the INI format. At the time of their creation, the files contain
default values for each of the supported Subversion options, mostly commented out and grouped with
textual descriptions about how the values for the key affect Subversion's behavior. To change a certain
behavior, you need only to load the appropriate configuration file into a text editor, and modify the desired option's value. If at any time you wish to have the default configuration settings restored, you can
simply remove (or rename) your configuration directory, and then run some innocuous svn command,
such as svn --version. A new configuration directory with the default contents will be created.
The per-user configuration area also contains a cache of authentication data. The auth directory holds a
set of subdirectories that contain pieces of cached information used by Subversion's various supported
authentication methods. This directory is created in such a way that only the user herself has permission
to read its contents.
Configuration and the Windows Registry
In addition to the usual INI-based configuration area, Subversion clients running on Windows platforms
may also use the Windows registry to hold the configuration data. The option names and their values are
the same as in the INI files. The “file/section” hierarchy is preserved as well, though addressed in a
slightly different fashion—in this schema, files and sections are just levels in the registry key tree.
HKEY_LOCAL_MACHINE\Software\\Subversion key. For example, the
global-ignores option, which is in the miscellany section of the config file, would be found
Registry-based configuration options are parsed before their file-based counterparts, so are overridden
by values found in the configuration files. In other words, configuration priority is granted in the following order on a Windows system:
Command-line options
The per-user INI files
The per-user Registry values
The system-wide INI files
The system-wide Registry values
Also, the Windows Registry doesn't really support the notion of something being “commented out”.
However, Subversion will ignore any option key whose name begins with a hash (#) character. This allows you to effectively comment out a Subversion option without deleting the entire key from the Registry, obviously simplifying the process of restoring that option.
The svn command-line client never attempts to write to the Windows Registry, and will not attempt to
create a default configuration area there. You can create the keys you need using the REGEDIT program. Alternatively, you can create a .reg file, and then double-click on that file from the Explorer
shell, which will cause the data to be merged into your registry.
Advanced Topics
Example 7.1. Sample Registration Entries (.reg) File.
"#global-ignores"="*.o *.lo *.la #*# .*.rej *.rej .*~ *~ .#*"
The previous example shows the contents of a .reg file which contains some of the most commonly
used configuration options and their default values. Note the presence of both system-wide (for network
proxy-related options) and per-user settings (editor programs and password storage, among others). Also
note that all the options are effectively commented out. You need only to remove the hash (#) character
from the beginning of the option names, and set the values as you desire.
Configuration Options
In this section, we will discuss the specific run-time configuration options that are currently supported
by Subversion.
The servers file contains Subversion configuration options related to the network layers. There are
two special section names in this file—groups and global. The groups section is essentially a
cross-reference table. The keys in this section are the names of other sections in the file; their values are
Advanced Topics
globs—textual tokens which possibly contain wildcard characters—that are compared against the hostnames of the machine to which Subversion requests are sent.
beanie-babies = *
collabnet =
When Subversion is used over a network, it attempts to match the name of the server it is trying to reach
with a group name under the groups section. If a match is made, Subversion then looks for a section in
the servers file whose name is the matched group's name. From that section it reads the actual network configuration settings.
The global section contains the settings that are meant for all of the servers not matched by one of the
globs under the groups section. The options available in this section are exactly the same as those
valid for the other server sections in the file (except, of course, the special groups section), and are as
This specifies the hostname of the proxy computer through which
your HTTP-based Subversion requests must pass. It defaults to an
empty value, which means that Subversion will not attempt to
route HTTP requests through a proxy computer, and will instead
attempt to contact the destination machine directly.
This specifies the port number on the proxy host to use. It defaults
to an empty value.
This specifies the username to supply to the proxy machine. It defaults to an empty value.
This specifies the password to supply to the proxy machine. It defaults to an empty value.
This specifies the amount of time, in seconds, to wait for a server
response. If you experience problems with a slow network connection causing Subversion operations to timeout, you should increase the value of this option. The default value is 0, which instructs the underlying HTTP library, Neon, to use its default timeout setting.
This specifies whether or not Subversion should attempt to compress network requests made to DAV-ready servers. The default
value is yes (though compression will only occur if that capability is compiled into the network layer). Set this to no to disable
compression, such as when debugging network transmissions.
This is an integer mask that the underlying HTTP library, Neon,
uses for choosing what type of debugging output to yield. The default value is 0, which will silence all debugging output. For more
information about how Subversion makes use of Neon, see Chapter 8, Developer Information.
A semi-colon delimited list of paths to files containing certificates
Advanced Topics
of the certificate authorities (or CAs) that are accepted by the
Subversion client when accessing the repository over HTTPS.
Set this variable to yes if you want Subversion to automatically
trust the set of "default" CAs that ship with OpenSSL.
If host (or set of hosts) requries an SSL client certificate, you'll
normally be prompted for a path to your certificate. By setting
this variable to that same path, Subversion will be able to find
your client certificate automatically without prompting you.
There's no standard place to store your certificate on disk; Subversion will grab it from any path you specify.
If your SSL client certificate file is encrypted by a passphrase,
Subversion will prompt you for the passphrase whenever the certificate is used. If you find this annoying (and don't mind storing
the password in the servers file), then you can set this variable
to the certificate's passphrase. You won't be prompted anymore.
The config file contains the rest of the currently available Subversion run-time options, those not related to networking. There are only a few options in use at this time, but they are again grouped into sections in expectation of future additions.
The auth section contains settings related to Subversion's authentication and authorization against the
repository. It contains:
This instructs Subversion to cache, or not to cache, authentication credentials
that are supplied by the user in response to server authentication challenges.
The default value is yes. Set this to no to disable this on-disk credential
caching. You can override this option for a single instance of the svn command using the --no-auth-cache command-line parameter (for those
subcommands that support it). For more information, see the section called
“Client Credentials Caching”.
The helpers section controls which external applications Subversion uses to accomplish its tasks.
Valid options in this section are:
This specifies the program Subversion will use to query the user for a
log message during a commit operation, such as when using svn commit without either the --message (-m) or --file (-F) options.
This program is also used with the svn propedit command—a temporary file is populated with the current value of the property the user
wishes to edit, and the edits take place right in the editor program (see
the section called “Properties”). This option's default value is empty. If
the option is not set, Subversion will fall back to checking the environment variables SVN_EDITOR, VISUAL, and EDITOR (in that order)
for an editor command.
This specifies the absolute path of a differencing program, used when
Subversion generates “diff” output (such as when using the svn diff
command). The default value is the path of the GNU diff utility, as determined by the Subversion source code build system.
Advanced Topics
This specifies the absolute path of a three-way differencing program.
Subversion uses this program to merge changes made by the user with
those received from the repository. The default value is the path of the
GNU diff3 utility, as determined by the Subversion source code build
This flag should be set to true if the program specified by the
diff3-cmd option accepts a --diff-program command-line parameter. Since the diff3-cmd option's default value is determined at
diff3-has-program-arg is, too.
The tunnels section allows you to define new tunnel schemes for use with svnserve and svn://
client connections. For more details, see the section called “SSH authentication and authorization”.
The miscellany section is where everything that doesn't belong elsewhere winds up. 27 In this section, you can find:
When running the svn status command, Subversion lists unversioned files
and directories along with the versioned ones, annotating them with a ?
character (see the section called “svn status”). Sometimes, it can be annoying to see uninteresting, unversioned items—for example, object files that
result from a program's compilation—in this display. The global-ignores option is a list of whitespace-delimited globs which describe the
names of files and directories that Subversion should not display unless they
are versioned. The default value is *.o *.lo *.la #*# .*.rej
*.rej .*~ *~ .#*.
You can override this option for a single instance of the svn status command by using the --no-ignore command-line flag. For information on
more fine-grained control of ignored items, see the section called
This instructs Subversion to automatically set properties on newly added or
imported files. The default value is no, so set this to yes to enable Autoprops.
The auto-props section controls the Subversion client's ability to automatically set properties on files when they are added or imported. It contains
any number of key-value pairs in the format REGEX = PROPNAME=PROPVALUE where REGEX is a regular expression that matches a
set of filenames and the rest of the line is the property and its value. Multiple
matches on a file will result in multiple propsets for that file; however, there
is no guarantee that auto-props will be applied in the order in which they are
listed in the config file, so you can't have one rule “override” another. You
can find several examples of auto-props usage in the config file. Lastly,
don't forget to set enable-auto-props to yes if you want to enable
This variable sets the default character set encoding for commit log messages. It's a permanent form of the --encoding option (see the section
called “svn Switches”.) The Subversion repository stores log messages in
UTF8, and assumes that your log message is written using your operating
system's native locale. You should specify a different encoding if your commit messages are written in any other encoding.
Anyone for potluck dinner?
Advanced Topics
Normally your working copy files have timestamps that reflect the last time
they were touched by any process, whether that be your own editor or by
some svn subcommand. This is generally convenient for people developing
software, because build systems often look at timestamps as a way of deciding which files need to be recompiled.
In other situations, however, it's sometimes nice for the working copy files
to have timestamps that reflect the last time they were changed in the repository. The svn export command always places these "last-commit timestamps" on trees that it produces. By setting this config variable to yes, the
svn checkout, svn update, svn switch, and svn revert commands will also
set last-commit timestamps on files that they touch.
We've already covered in detail how Subversion stores and retrieves various versions of files and directories in its repository. Whole chapters have been devoted to this most fundamental piece of functionality provided by the tool. And if the versioning support stopped there, Subversion would still be complete
from a version control perspective. But it doesn't stop there.
In addition to versioning your directories and files, Subversion provides interfaces for adding, modifying, and removing versioned metadata on each of your versioned directories and files. We refer to this
metadata as properties, and they can be thought of as two-column tables that map property names to arbitrary values attached to each item in your working copy. Generally speaking, the names and values of
the properties can be whatever you want them to be, with the constraint that the names must be humanreadable text. And the best part about these properties is that they, too, are versioned, just like the textual
contents of your files. You can modify, commit, and revert property changes as easily as committing
textual changes. And you receive other people's property changes as you update your working copy.
Other Properties in Subversion
Properties show up elsewhere in Subversion, too. Just as files and directories may have arbitrary property names and values attached to them, each revision as a whole may have arbitrary properties attached
to it. The same constraints apply—human-readable, text names and anything-you-want, binary
values—except that revision properties are not versioned. See the section called “Unversioned Properties” for more information on these unversioned properties.
In this section, we will examine the utility—both to users of Subversion, and to Subversion itself—of
property support. You'll learn about the property-related svn subcommands, and how property modifications affect your normal Subversion workflow. Hopefully, you'll be convinced that Subversion properties can enhance your version control experience.
Why Properties?
Properties can be very useful additions to your working copy. In fact, Subversion itself uses properties to
house special information, and as a way to denote that certain special processing might be needed. Likewise, you can use properties for your own purposes. Of course, anything you can do with properties you
could also do using regular versioned files, but consider the following example of Subversion property
Say you wish to design a website that houses many digital photos, and displays them with captions and a
datestamp. Now, your set of photos is constantly changing, so you'd like to have as much of this site automated as possible. These photos can be quite large, so as is common with sites of this nature, you want
Advanced Topics
to provide smaller thumbnail images to your site visitors. You can do this with traditional files. That is,
you can have your image123.jpg and an image123-thumbnail.jpg side-by-side in a directory. Or if you want to keep the filenames the same, you might have your thumbnails in a different directory, like thumbnails/image123.jpg. You can also store your captions and datestamps in a
similar fashion, again separated from the original image file. Soon, your tree of files is a mess, and
grows in multiples with each new photo added to the site.
Now consider the same setup using Subversion's file properties. Imagine having a single image file, image123.jpg, and then properties set on that file named caption, datestamp, and even thumbnail. Now your working copy directory looks much more manageable—in fact, it looks like there are
nothing but image files in it. But your automation scripts know better. They know that they can use svn
(or better yet, they can use the Subversion language bindings—see the section called “Using Languages
Other than C and C++”) to dig out the extra information that your site needs to display without having to
read an index file or play path manipulation games.
How (and if) you use Subversion properties is up to you. As we mentioned, Subversion has it own uses
for properties, which we'll discuss a little later in this chapter. But first, let's discuss how to manipulate
options using the svn program.
Manipulating Properties
The svn command affords a few ways to add or modify file and directory properties. For properties with
short, human-readable values, perhaps the simplest way to add a new property is to specify the property
name and value on the command-line of the propset subcommand.
$ svn propset copyright '(c) 2003 Red-Bean Software' calc/button.c
property `copyright' set on 'calc/button.c'
But we've been touting the flexibility that Subversion offers for your property values. And if you are
planning to have a multi-line textual, or even binary, property value, you probably do not want to supply
that value on the command-line. So the propset subcommand takes a --file (-F) option for specifying the name of a file which contains the new property value.
$ svn propset license -F /path/to/LICENSE calc/button.c
property `license' set on 'calc/button.c'
In addition to the propset command, the svn program supplies the propedit command. This command
uses the configured editor program (see the section called “Config”) to add or modify properties. When
you run the command, svn invokes your editor program on a temporary file that contains the current
value of the property (or which is empty, if you are adding a new property). Then, you just modify that
value in your editor program until it represents the new value you wish to store for the property, save the
temporary file, and then exit the editor program. If Subversion detects that you've actually changed the
existing value of the property, it will accept that as the new property value. If you exit your editor without making any changes, no property modification will occur.
$ svn propedit copyright calc/button.c ### exit the editor without changes
No changes to property `copyright' on `calc/button.c'
We should note that, as with other svn subcommands, those related to properties can act on multiple
paths at once. This enables you to modify properties on whole sets of files with a single command. For
example, we could have done:
Advanced Topics
$ svn propset copyright '(c) 2002 Red-Bean Software' calc/*
property `copyright' set on 'calc/Makefile'
property `copyright' set on 'calc/button.c'
property `copyright' set on 'calc/integer.c'
All of this property adding and editing isn't really very useful if you can't easily get the stored property
value. So the svn program supplies two subcommands for displaying the names and values of properties
stored on files and directories. The svn proplist command will list the names of properties that exist on
a path. Once you know the names of the properties on the node, you can request their values individually
using svn propget. This command will, given a path (or set of paths) and a property name, print the
value of the property to the standard output stream.
$ svn proplist calc/button.c
Properties on 'calc/button.c':
$ svn propget copyright calc/button.c
(c) 2003 Red-Bean Software
There's even a variation of the proplist command that will list both the name and value of all of the
properties. Simply supply the --verbose (-v) option.
$ svn proplist --verbose calc/button.c
Properties on 'calc/button.c':
copyright : (c) 2003 Red-Bean Software
license : ================================================================
Copyright (c) 2003 Red-Bean Software. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions, and the recipe for Fitz's famous
The last property-related subcommand is propdel. Since Subversion allows you to store properties with
empty values, you can't remove a property altogether using propedit or propset. For example, this command will not yield the desired effect:
$ svn propset license '' calc/button.c
property `license' set on 'calc/button.c'
$ svn proplist --verbose calc/button.c
Properties on 'calc/button.c':
copyright : (c) 2003 Red-Bean Software
license :
You need to use the propdel command to delete properties altogether. The syntax is similar to the other
property commands:
Advanced Topics
$ svn propdel license calc/button.c
property `license' deleted from ''.
$ svn proplist --verbose calc/button.c
Properties on 'calc/button.c':
copyright : (c) 2003 Red-Bean Software
Now that you are familiar with all of the property-related svn subcommands, let's see how property
modifications affect the usual Subversion workflow. As we mentioned earlier, file and directory properties are versioned, just like your file contents. As a result, Subversion provides the same opportunities
for merging—in cleanly or conflicting fashions—someone else's modifications into your own.
Modifying Revision Properties
Remember those unversioned revision properties? You can modify those, too, with the svn program.
Simply add the --revprop command-line parameter, and specify the revision whose property you
wish to modify. Since revisions are global, you don't need to specify a path in this case as long as you
are positioned in the working copy of the repository whose revision property you wish to modify. For
example, you might want to replace the commit log message of an existing revision. 28
$ svn propset svn:log '* button.c: Fix a compiler warning.' -r11 --revprop
property `svn:log' set on repository revision '11'
Note that the ability to modify these unversioned properties must be explicitly added by the repository
administrator (see the section called “Hook Scripts”). Since the properties aren't versioned, you run the
risk of losing information if you aren't careful with your edits. The repository administrator can setup
methods to protect against this lossage, but by default, modification of unversioned properties is disabled.
And as with file contents, your property changes are local modifications, only made permanent when
you commit them to the repository with svn commit. Your property changes can be easily unmade,
too—the svn revert command will restore your files and directories to their un-edited states, contents,
properties, and all. Also, you can receive interesting information about the state of your file and directory properties by using the svn status and svn diff commands.
$ svn status calc/button.c
$ svn diff calc/button.c
Property changes on: calc/button.c
Name: copyright
+ (c) 2003 Red-Bean Software
Notice how the status subcommand displays M in the second column instead of the first. That is because
we have modified the properties on calc/button.c, but not modified its textual contents. Had we
changed both, we would have seen M in the first column, too (see the section called “svn status”).
Fixing spelling errors, grammatical gotchas, and “just-plain-wrongness” in commit log messages is perhaps the most common
use-case for the --revprop option.
Advanced Topics
Property Conflicts
As with file contents, local property modifications can conflict with changes committed by someone
else. If you update your working copy directory and receive property changes on a versioned resource
that clash with your own, Subversion will report that the resource is in a conflicted state.
% svn update calc
M calc/
C calc/button.c
Updated to revision 143.
Subversion will also create, in the same directory as the conflicted resource, a file with a .prej extension which contains the details of the conflict. You should examine the contents of this file so you can
decide how to resolve the conflict. Until the conflict is resolved, you will see a C in the second column
of svn status output for that resource, and attempts to commit your local modifications will fail.
$ svn status calc
$ cat calc/button.c.prej
prop `linecount': user set to '1256', but update set to '1301'.
To resolve property conflicts, simply ensure that the conflicting properties contain the values that they
should, and then use the svn resolved command to alert Subversion that you have manually resolved the
You might also have noticed the non-standard way that Subversion currently displays property differences. You can still run svn diff and redirect the output to create a usable patch file. The patch program
will ignore property patches—as a rule, it ignores any noise it can't understand. This does unfortunately
mean that to fully apply a patch generated by svn diff, any property modifications will need to be applied by hand.
As you can see, the presence of property modifications has no outstanding effect on the typical Subversion workflow. Your general patterns of updating your working copy, checking the status of your files
and directories, reporting on the modifications you have made, and committing those modifications to
the repository are completely immune to the presence or absence of properties. The svn program has
some additional subcommands for actually making property changes, but that is the only noticeable
Special properties
Subversion has no particular policy regarding properties—you can use them for any purpose. Subversion
asks only that you not use property names that begin with the prefix svn:. That's the namespace that it
sets aside for its own use. In fact, Subversion defines certain properties that have magical effects on the
files and directories to which they are attached. In this section, we'll untangle the mystery, and describe
how these special properties make your life just a little easier.
The svn:executable property is used to control a versioned file's filesystem-level execute permission bit in a semi-automated way. This property has no defined values—its mere presence indicates a
Advanced Topics
desire that the execute permission bit be kept enabled by Subversion. Removing this property will restore full control of the execute bit back to the operating system.
On many operating systems, the ability to execute a file as a command is governed by the presence of an
execute permission bit. This bit usually defaults to being disabled, and must be explicitly enabled by the
user for each file that needs it. In a working copy, new files are being created all the time as new versions of existing files are received during an update. This means that you might enable the execute bit on
a file, then update your working copy, and if that file was changed as part of the update, its execute bit
might get disabled. So, Subversion provides the svn:executable property as a way to keep the execute bit enabled.
This property has no effect on filesystems that have no concept of an executable permission bit, such as
FAT32 and NTFS. 29 Also, although it has no defined values, Subversion will force its value to * when
setting this property. Finally, this property is valid only on files, not on directories.
The svn:mime-type property serves many purposes in Subversion. Besides being a general-purpose
storage location for a file's Multipurpose Internet Mail Extensions (MIME) classification, the value of
this property determines several behavioral characteristics of Subversion itself.
For example, if a file's svn:mime-type property is set to a non-text MIME type (generally, something that doesn't begin with text/, though there are exceptions), Subversion will assume that the file
contains binary—that is, not human-readable—data. One of the benefits that Subversion typically provides is contextual, line-based merging of changes received from the server during an update into your
working file. But for files believed to contain binary data, there is no concept of a “line”. So, for those
files, Subversion does not attempt to perform contextual merges during updates. Instead, any time you
have locally modified a binary working copy file that is also being updated, your file is renamed with a
.orig extension, and then Subversion stores a new working copy file that contains the changes received during the update, but not your own local modifications, at the original filename. This behavior is
really for the protection of the user against failed attempts at performing contextual merges on files that
simply cannot be contextually merged.
Subversion assists users by running a binary-detection algorithm in the svn import and svn add subcommands. These subcommands use a heuristic to guess at a file's “binary-ness”, and then set the
svn:mime-type property to application/octet-stream (the generic “this is a collection of
bytes” MIME type) on any files that are deemed binary. If Subversion guesses wrong, or if you wish to
set the svn:mime-type property to something more accurate—perhaps image/png or application/x-shockwave-flash—you can always remove or hand-edit the property.
Finally, if the svn:mime-type property is set, then the Subversion Apache module will use its value
to populate the Content-type: HTTP header when responding to GET requests. This gives a crucial
clue about how to display a file when perusing your repository with a web browser.
The svn:ignore property contains a list of file patterns which certain Subversion operations will ignore. Perhaps the most commonly used special property, it works in conjunction with the globalignores run-time configuration option (see the section called “Config”) to filter unversioned files and
directories out of commands like svn status.
The rationale behind the svn:ignore property is easily explained. Subversion does not assume that
every file or subdirectory in a working copy directory is intended for version control. Resources must be
explicitly placed under Subversion's management using the svn add command. As a result, there are often many resources in a working copy that are not versioned.
Now, the svn status command displays as part of its output every unversioned file or subdirectory in a
working copy that is not already filtered out by the global-ignores option (or its built-in default
The Windows filesystems use file extensions (such as .EXE, .BAT, and .COM) to denote executable files.
Advanced Topics
value). This is done so that users can see if perhaps they've forgotten to add a resource to version control.
But Subversion cannot possibly guess the names of every resource that should be ignored. Also, quite
often there are things that should be ignored in every working copy of a particular repository. To force
every user of that repository to add patterns for those resources to their run-time configuration areas
would be not just a burden, but has the potential to clash with the configuration needs of other working
copies that the user has checked out.
The solution is to store ignore patterns that are unique to the resources likely to appear in a given directory with the directory itself. Common examples of unversioned resources that are basically unique to a
directory, yet likely to appear there, include output from program compilations. Or—to use an example
more appropriate to this book—the HTML, PDF, or PostScript files generated as the result of a conversion of some source DocBook XML files to a more legible output format.
Ignore Patterns for CVS Users
The Subversion svn:ignore property is very similar in syntax and function to the CVS
.cvsignore file. In fact, if you are migrating a CVS working copy to Subversion, you can directly
migrate the ignore patterns by using the .cvsignore file as input file to the svn propset command:
$ svn propset svn:ignore -F .cvsignore .
property `svn:ignore' set on '.'
There are, however, some differences in the ways that CVS and Subversion handle ignore patterns. The
two systems use the ignore patterns at some different times, and there are slight discrepancies in what
the ignore patterns apply to. Also, Subversion does not recognize the use of the ! pattern as a reset back
to having no ignore patterns at all.
For this purpose, the svn:ignore property is the solution. Its value is a multi-line collection of file
patterns, one pattern per line. The property is set on the directory in which you wish the patterns to be
applied. 30 For example, say you have the following output from svn status:
$ svn status calc
In this example, you have made some property modifications to button.c, but in your working copy
you also have some unversioned files, in this case, the latest calculator program that you've compiled from your source code, a source file named data.c, and a set of debugging output log files. Now,
you know that your build system always results in the calculator program being generated. 31 And
you know that your test suite always leaves those debugging log files lying around. These facts are true
for all working copies, not just your own. And you know that you aren't interested in seeing those things
every time you run svn status. So you use svn propedit svn:ignore calc to add some ignore patterns to
the calc directory. For example, you might add this as the new value of the svn:ignore property:
The patterns are strictly for that directory—they do not carry recursively into subdirectories.
Isn't that the whole point of a build system?
Advanced Topics
After you've added this property, you will now have a local property modification on the calc directory. But notice what else is different about your svn status output:
$ svn status
Now, all the cruft is missing from the output! Of course, those files are still in your working copy. Subversion is simply not reminding you that they are present and unversioned. And now with all the trivial
noise removed from the display, you are left with more interesting items— such as that source code file
that you probably forgot to add to version control.
If you want to see the ignored files, you can pass the --no-ignore option to subversion:
$ svn status --no-ignore
Subversion has the ability to substitute keywords—pieces of useful, dynamic information about a versioned file—into the contents of the file itself. Keywords generally describe information about the last
time the file was known to be modified. Because this information changes each time the file changes,
and more importantly, just after the file changes, it is a hassle for any process except the version control
system to keep the data completely up-to-date. Left to human authors, the information would inevitably
grow stale.
For example, say you have a document in which you would like to display the last date on which it was
modified. You could burden every author of that document to, just before committing their changes, also
tweak the part of the document that describes when it was last changed. But sooner or later, someone
would forget to do that. Instead simply ask Subversion to perform keyword substitution on the
LastChangedDate keyword. You control where the keyword is inserted into your document by placing a keyword anchor at the desired location in the file. This anchor is just a string of text formatted as
Subversion defines the list of keywords available for substitution. That list contains the following five
keywords, some of which have shorter aliases that you can also use:
This keyword describes the last time the file was known to have been
$LastChangedDate: 2002-07-22 21:42:37 -0700 (Mon,
22 Jul 2002) $. It may be abbreviated as Date.
This keyword describes the last known revision in which this file
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$LastChangedRevision: 144 $. It may be abbreviated as Rev.
This keyword describes the last known user to change this file in the
repository, and looks something like $LastChangedBy: harry $.
It may be abbreviated as Author
This keyword describes the full URL to the latest version of the file in the
$HeadURL: $. It may be
abbreviated as URL.
This keyword is a compressed combination of the other keywords. Its
substitution looks something like $Id: calc.c 148 2002-07-28
21:30:43Z sally $, and is interpreted to mean that the file
calc.c was last changed in revision 148 on the evening of July 28,
2002 by the user sally.
Simply adding keyword anchor text to your file does nothing special. Subversion will never attempt to
perform textual substitutions on your file contents unless explicitly asked to do so. After all, you might
be writing a document 32 about how to use keywords, and you don't want Subversion to substitute your
beautiful examples of un-substituted keyword anchors!
To tell Subversion whether or not to substitute keywords on a particular file, we again turn to the property-related subcommands. The svn:keywords property, when set on a versioned file, controls which
keywords will be substituted on that file. The value is a space-delimited list of the keyword names or
aliases found in the previous table.
For example, say you have a versioned file named weather.txt that looks like this:
Here is the latest report from the front lines.
Cumulus clouds are appearing more frequently as summer approaches.
With no svn:keywords property set on that file, Subversion will do nothing special. Now, let's enable substitution of the LastChangedDate keyword.
$ svn propset svn:keywords "LastChangedDate Author" weather.txt
property `svn:keywords' set on 'weather.txt'
Now you have made a local property modification on the weather.txt file. You will see no changes
to the file's contents (unless you made some of your own prior to setting the property). Notice that the
file contained a keyword anchor for the Rev keyword, yet we did not include that keyword in the property value we set. Subversion will happily ignore requests to substitute keywords that are not present in
the file, and will not substitute keywords that are not present in the svn:keywords property value.
Keywords and Spurious Differences
The user-visible result of keyword substitution might lead you to think that every version of a file with
that feature in use differs from the previous version in at least the area where the keyword anchor was
placed. However, this is actually not the case. While checking for local modifications during svn diff,
and before transmitting those local modifications during svn commit, Subversion “un-substitutes” any
… or maybe even a section of a book …
Advanced Topics
keywords that it previously substituted. The result is that the versions of the file that are stored in the
repository contain only the real modifications that users make to the file.
Immediately after you commit this property change, Subversion will update your working file with the
new substitute text. Instead of seeing your keyword anchor $LastChangedDate$, you'll see its substituted result. That result also contains the name of the keyword, and continues to be bounded by the
dollar sign ($) characters. And as we predicted, the Rev keyword was not substituted because we didn't
ask for it to be.
Here is the latest report from the front lines.
$LastChangedDate: 2002-07-22 21:42:37 -0700 (Mon, 22 Jul 2002) $
Cumulus clouds are appearing more frequently as summer approaches.
If someone else now commits a change to weather.txt, your copy of that file will continue to display the same substituted keyword value as before—until you update your working copy. At that time
the keywords in your weather.txt file will be re-substituted with information that reflects the most
recent known commit to that file.
Unless otherwise noted using a versioned file's svn:mime-type property, Subversion assumes the
file contains human-readable data. Generally speaking, Subversion only uses this knowledge to determine if contextual difference reports for that file are possible. Otherwise, to Subversion, bytes are bytes.
This means that by default, Subversion doesn't pay any attention to the type of end-of-line (EOL) markers used in your files. Unfortunately, different operating system use different tokens to represent the end
of a line of text in a file. For example, the usual line ending token used by software on the Windows
platform is a pair of ASCII control characters—carriage return (CR) and line feed (LF). Unix software,
however, just uses the LF character to denote the end of a line.
Not all of the various tools on these operating systems are prepared to understand files that contain line
endings in a format that differs from the native line ending style of the operating system on which they
are running. Common results are that Unix programs treat the CR character present in Windows files as
a regular character (usually rendered as ^M), and that Windows programs combine all of the lines of a
Unix file into one giant line because no carriage return-linefeed (or CRLF) character combination was
found to denote the end of line.
This sensitivity to foreign EOL markers can become frustrating for folks who share a file across different operating systems. For example, consider a source code file, and developers that edit this file on both
Windows and Unix systems. If all the developers always use tools which preserve the line ending style
of the file, no problems occur.
But in practice, many common tools either fail to properly read a file with foreign EOL markers, or they
convert the file's line endings to the native style when the file is saved. If the former is true for a developer, he has to use an external conversion utility (such as dos2unix or its companion, unix2dos) to prepare the file for editing. The latter case requires no extra preparation. But both cases result in a file that
differs from the original quite literally on every line! Prior to committing his changes, the user has two
choices. Either he can use a conversion utility to restore the modified file to the same line ending style
that it was in before his edits were made. Or, he can simply commit the file—new EOL markers and all.
The result of scenarios like these include wasted time and unnecessary modifications to committed files.
Wasted time is painful enough. But when commits change every line in a file, this complicates the job of
determining which of those lines were changed in a non-trivial way. Where was that bug really fixed?
On what line was a syntax error introduced?
Advanced Topics
The solution to this problem is the svn:eol-style property. When this property is set to a valid
value, Subversion uses it to determine what special processing to perform on the file so that the file's
line ending style isn't flip-flopping with every commit that comes from a different operating system. The
valid values are:
This causes the file to contain the EOL markers that are native to the operating system on
which Subversion was run. In other words, if a user on a Windows machine checks out a
working copy that contains a file with a svn:eol-style property set to native, that file
will contain CRLF EOL markers. A unix user checking out a working copy which contains
the same file will see LF EOL markers in his copy of the file.
Note that Subversion will actually store the file in the repository using normalized LF EOL
markers regardless of the operating system. This is basically transparent to the user, though.
This causes the file to contain CRLF sequences for EOL markers, regardless of the operating
system in use.
This causes the file to contain LF characters for EOL markers, regardless of the operating
system in use.
This causes the file to contain CR characters for EOL markers, regardless of the operating
system in use. This line ending style is not very common. It was used on older Macintosh
platforms (on which Subversion doesn't even run).
The svn:externals property contains instructions for Subversion to populate a versioned directory
with one or more other checked-out Subversion working copies. For more information on this keyword
and its use, see the section called “Externals Definitions”.
Externals Definitions
Sometimes it is useful to construct a working copy that is made out of a number of different checkouts.
For example, you may want different subdirectories to come from different locations in a repository, or
perhaps from different repositories altogether. You could certainly setup such a scenario by hand—using
svn checkout to create the sort of nested working copy structure you are trying to achieve. But if this
layout is important for everyone who uses your repository, every other user will need to perform the
same checkout operations that you did.
Fortunately, Subversion provides support for externals definitions. An externals definition is a mapping
of a local directory to the URL—and possibly a particular revision—of a versioned resource. In Subversion, you declare externals definitions in groups using the svn:externals property. This property is
set on a versioned directory, and its value is a multi-line table of subdirectories (relative to the versioned
directory on which the property is set) and Subversion repository URLs.
$ svn propget svn:externals calc
third-party/skins/toolkit -r21
The convenience of the svn:externals property is that once it is set on a versioned directory, everyone who checks out a working copy with that directory also gets the benefit of the externals definition.
In other words, once one person has made the effort to define those nested working copy checkouts, no
one else has to bother—Subversion will, upon checkout of the original working copy, also checkout the
Advanced Topics
external working copies.
Note the previous externals definition example. When someone checks out a working copy of the calc
directory, Subversion also continues to checkout the items found in its externals definition.
$ svn checkout
A calc
A calc/Makefile
A calc/integer.c
A calc/button.c
Checked out revision 148.
Fetching external item into calc/third-party/sounds
A calc/third-party/sounds/ding.ogg
A calc/third-party/sounds/dong.ogg
A calc/third-party/sounds/clang.ogg
A calc/third-party/sounds/bang.ogg
A calc/third-party/sounds/twang.ogg
Checked out revision 14.
Fetching external item into calc/third-party/skins
If you need to change the externals definition, you can do so using the regular property modification
subcommands. When you commit a change to the svn:externals property, Subversion will synchronize the checked-out items against the changed externals definition when you next run svn update.
The same thing will happen when others update their working copies and receive your changes to the
externals definition.
The svn status command also recognizes externals definitions, displaying a status code of X for the disjoint subdirectories into which externals are checked out, and then recursing into those subdirectories to
display the status of the external items themselves.
The support that exists for externals definitions in Subversion today can be a little misleading, though.
The auxiliary working copies created via the externals definition support are still disconnected from the
primary working copy. And Subversion still only truly operates on non-disjoint working copies. So, for
example, if you want to commit changes that you've made in one or more of the auxiliary working
copies, you must run svn commit explicitly on those working copies, not on the primary working copy.
Vendor branches
As is especially the case when developing software, the data that you maintain under version control is
often closely related to, or perhaps dependent upon, someone else's data. Generally, the needs of your
project will dictate that you stay as up-to-date as possible with the data provided by that external entity
without sacrificing the stability of your own project. This scenario plays itself out all the anytime—where that the information generated by one group of people has a direct effect on that which is
generated by another group.
For example, software developers might be working on an application which makes use of a third-party
library. Subversion has just such a relationship with the Apache Portable Runtime library (see the section called “The Apache Portable Runtime Library”). The Subversion source code depends on the APR
library for all its portability needs. In earlier stages of Subversion's development, the project closely
tracked APR's changing API, always sticking to the “bleeding edge” of the library's code churn. Now
that both APR and Subversion have matured, Subversion attempts to synchronize with APR's library
API only at well-tested, stable release points.
Now, if your project depends on someone else's information, there are several ways that you could at123
Advanced Topics
tempt to synchronize that information with your own. Most painfully, you could issue oral or written instructions to all the contributors of your project, telling them to make sure that they have the specific
versions of that third-party information that your project needs. If the third-party information is maintained in a Subversion repository, you could also use Subversion's externals definitions to effectively
“pin down” specific versions of that information to some location in your own working copy directory
(see the section called “Externals Definitions”).
But sometimes you want to maintain custom modifications to third-party data in your own version control system. Returning to the software development example, programmers might need to make modifications to that third-party library for their own purposes. These modifications might include new functionality or bug fixes, maintained internally only until they become part of an official release of the
third-party library. Or the changes might never be relayed back to the library maintainers, existing solely
as custom tweaks to make the library further suit the needs of the software developers.
Now you face an interesting situation. Your project could house its custom modifications to the thirdparty data in some disjointed fashion, such as using patch files or full-fledged alternate versions of files
and directories. But these quickly become maintenance headaches, requiring some mechanism by which
to apply your custom changes to the third-party data, and necessitating regeneration of those changes
with each successive version of the third-party data that you track.
The solution to this problem is to use vendor branches. A vendor branch is a directory tree in your own
version control system that contains information provided by a third-party entity, or vendor. Each version of the vendor's data that you decide to absorb into your project is called a vendor drop.
Vendor branches provide two key benefits. First, by storing the currently supported vendor drop in your
own version control system, the members of your project never need to question whether they have the
right version of the vendor's data. They simply receive that correct version as part of their regular working copy updates. Secondly, because the data lives in your own Subversion repository, you can store
your custom changes to it in-place—you have no more need of an automated (or worse, manual) method
for swapping in your customizations.
General Vendor Branch Management Procedure
Managing vendor branches generally works like this. You create a top-level directory (such as /
vendor) to hold the vendor branches. Then you import the third party code into a subdirectory of that
top-level directory. You then copy that subdirectory into your main development branch (for example, /
trunk) at the appropriate location. You always make your local changes in the main development
branch. With each new release of the code you are tracking you bring it into the vendor branch and
merge the changes into /trunk, resolving whatever conflicts occur between your local changes and the
upstream changes.
Perhaps an example will help to clarify this algorithm. We'll use a scenario where your development
team is creating a calculator program that links against a third-party complex number arithmetic library,
libcomplex. We'll begin with the initial creation of the vendor branch, and the import of the first vendor
$ svn import /path/to/libcomplex-1.0 \ \
-m 'importing initial 1.0 vendor drop'
We now have the current version of the libcomplex source code in
/vendor/libcomplex/current. Now, we tag that version (see the section called “Tags”) and then
copy it into the main development branch so we can make our customizations to it.
Advanced Topics
$ svn copy
-m 'tagging libcomplex-1.0'
$ svn copy \
-m 'bringing libcomplex-1.0 into the main branch'
We check out our project's main branch—which now includes a copy of the first vendor drop—and we
get to work customizing the libcomplex code. Before we know it, our modified version of libcomplex is
now completely integrated into our calculator program. 33
A few weeks later, the developers of libcomplex release a new version of their library—version
1.1—which contains some features and functionality that we really want. But we'd like to upgrade to
this new version without losing our customizations to the existing version. As you might have guessed,
what we essentially would like to do is to replace our current baseline version of libcomplex 1.0 with a
copy of libcomplex 1.1, and then re-apply the custom modifications we previously made to that library
to the new version.
To perform this upgrade, we checkout a copy of our vendor branch, and replace the current version
with the new libcomplex 1.1 source code. After committing this change, our current branch now contains the new vendor drop. We tag the new version, and then merge the differences between the tag of
the previous version and the new current version into our main development branch.
$ cd working-copies/calc
$ svn merge
\ \
… # resolve all the conflicts between their changes and our changes
$ svn commit -m 'merging libcomplex-1.1 into the main branch'
In the trivial use-case, the new version of our third-party tool would look, from a files-and-directories
point of view, just like the previous version. In other words, none of the libcomplex source files would
have been deleted, renamed or moved to different locations—in short, in a perfect world, our modifications would apply cleanly to the new version of the library, with absolutely no complications or conflicts.
But things aren't always that simple, and in fact it is quite common for source files to get moved around
between releases of software. This complicates the process of ensuring that our modifications are still
valid for the new version of code, and can quickly degrade into a situation where we have to manually
recreate our customizations in the new version. Once Subversion knows about the history of a given
source file—including all its previous locations—the process of merging in the new version of the library is pretty simple. But we are responsible for telling Subversion how the source file layout changed
from vendor drop to vendor drop.
Vendor drops that contain more than a few deletes, additions and moves complicate the process of upgrading to each successive version of the third-party data. So Subversion supplies the
script to assist with this process. This script automates the importing steps we mentioned in the general
vendor branch management procedure to make sure that mistakes are minimized. You will still be responsible for using the merge commands to merge the new versions of the third-party data into your
main development branch, but can help you more quickly and easily arrive at that
And entirely bug-free, of course!
Advanced Topics
In short, is an enhancement to svn import that has several important characteristics:
It can be run at any point in time to bring an existing directory in the repository to exactly match an
external directory, performing all the necessary adds and deletes, and optionally performing moves,
It takes care of complicated series of operations between which Subversion requires an intermediate
commit—such as before renaming a file or directory twice.
It will optionally tag the newly imported directory.
It will optionally add arbitrary properties to files and directories that match a regular expression. takes three mandatory arguments. The first argument is the URL to the base Subversion directory to work in. This argument is followed by the URL—relative to the first argument—into
which the current vendor drop will be imported. Finally, the third argument is the local directory to import. Using our previous example, a typical run of might look like:
$ \
You can indicate that you'd like to tag the new vendor drop by passing the -t command-line option and specifying a tag name. This tag is another URL relative to the first program argument.
$ -t libcomplex-1.1
\ \
When you run, it examines the contents of your existing “current” vendor drop, and
compares them with the proposed new vendor drop. In the trivial case, there will be no files that are in
one version and not the other, and the script will perform the new import without incident. If, however,
there are discrepancies in the file layouts between versions, will prompt you for how
you would like to resolve those differences. For example, you will have the opportunity to tell the script
that you know that the file math.c in version 1.0 of libcomplex was renamed to arithmetic.c in
libcomplex 1.1. Any discrepancies not explained by moves are treated as regular additions and deletions.
The script also accepts a separate configuration file for setting properties on files and directories matching a regular expression that are added to the repository. This configuration file is specified to using the -p command-line option. Each line of the configuration file is a whitespacedelimited set of two or four values: a Perl-style regular expression to match the added path against, a
control keyword (either break or cont), and then optionally a property name and value.
Advanced Topics
For each added path, the configured property changes whose regular expression matches the path are applied in order, unless the control specification is break (which means that no more property changes
should be applied to that path). If the control specification is cont—an abbreviation for
continue—then matching will continue with the next line of the configuration file.
Any whitespace in the regular expression, property name, or property value must be surrounded by
either single or double quote characters. You can escape quote characters that are not used for wrapping
whitespace by preceding them with a backslash (\) character. The backslash escapes only quotes when
parsing the configuration file, so do not protect any other characters beyond what is necessary for the
regular expression.
Chapter 8. Developer Information
Subversion is an open-source software project developed under an Apache-style software license. The
project is financially backed by CollabNet, Inc., a California-based software development company. The
community that has formed around the development of Subversion always welcomes new members who
can donate their time and attention to the project. Volunteers are encouraged to assist in any way they
can, whether that means finding and diagnosing bugs, refining existing source code, or fleshing out
whole new features.
This chapter is for those who wish to assist in the continued evolution of Subversion by actually getting
their hands dirty with the source code. We will cover some of the software's more intimate details, the
kind of technical nitty-gritty that those developing Subversion itself—or writing entirely new tools
based on the Subversion libraries—should be aware of. If you don't foresee yourself participating with
the software at such a level, feel free to skip this chapter with confidence that your experience as a Subversion user will not be affected.
Layered Library Design
Subversion has a modular design, implemented as a collection of C libraries. Each library has a welldefined purpose and interface, and most modules are said to exist in one of three main layers—the
Repository Layer, the Repository Access (RA) Layer, or the Client Layer. We will examine these layers
shortly, but first, see our brief inventory of Subversion's libraries in Table 7-1. For the sake of consistency, we will refer to the libraries by their extensionless Unix library names (e.g.: libsvn_fs, libsvn_wc,
Table 8.1. A Brief Inventory of the Subversion Libraries
Primary interface for client programs
Tree and text differencing routines
The Subversion filesystem library
Repository Access commons and module loader
The WebDAV Repository Access module
The local Repository Access module
A proprietary protocol Repository Access module
Repository interface
Miscellaneous helpful subroutines
The working copy management library
Apache module for mapping WebDAV operations
to Subversion ones
The fact that the word "miscellaneous" only appears once in Table 7-1 is a good sign. The Subversion
development team is serious about making sure that functionality lives in the right layer and libraries.
Perhaps the greatest advantage of the modular design is its lack of complexity from a developer's point
of view. As a developer, you can quickly formulate that kind of "big picture" that allows you to pinpoint
the location of certain pieces of functionality with relative ease.
And what could better help a developer gain a "big picture" perspective than a big picture? To help you
understand how the Subversion libraries fit together, see Figure 7-1, a diagram of Subversion's layers.
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Program flow begins at the top of the diagram (initiated by the user) and flows "downward".
Figure 8.1. Subversion's "Big Picture"
Another benefit of modularity is the ability to replace a given module with a whole new library that implements the same API without affecting the rest of the code base. In some sense, this happens within
Subversion already. The libsvn_ra_dav, libsvn_ra_local, and libsvn_ra_svn all implement the same interface. And all three communicate with the Repository Layer— libsvn_ra_dav and libsvn_ra_svn do so
across a network, and libsvn_ra_local connects to it directly.
The client itself also highlights modularity in the Subversion design. While Subversion currently comes
with only a command-line client program, there are already a few other programs being developed by
third parties to act as GUIs for Subversion. Again, these GUIs use the same APIs that the stock command-line client does. Subversion's libsvn_client library is the one-stop shop for most of the functionality necessary for designing a working Subversion client (see the section called “Client Layer”).
Repository Layer
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When referring to Subversion's Repository Layer, we're generally talking about two libraries—the
repository library, and the filesystem library. These libraries provide the storage and reporting mechanisms for the various revisions of your version-controlled data. This layer is connected to the Client
Layer via the Repository Access Layer, and is, from the perspective of the Subversion user, the stuff at
the "other end of the line."
The Subversion Filesystem is accessed via the libsvn_fs API, and is not a kernel-level filesystem that
one would install in an operating system (like the Linux ext2 or NTFS), but a virtual filesystem. Rather
than storing "files" and "directories" as real files and directories (as in, the kind you can navigate
through using your favorite shell program), it uses a database system for its back-end storage mechanism. Currently, the database system in use is Berkeley DB. 34 However, there has been considerable interest by the development community in giving future releases of Subversion the ability to use other
back-end database systems, perhaps through a mechanism such as Open Database Connectivity
The filesystem API exported by libsvn_fs contains the kinds of functionality you would expect from any
other filesystem API: you can create and remove files and directories, copy and move them around,
modify file contents, and so on. It also has features that are not quite as common, such as the ability to
add, modify, and remove metadata ("properties") on each file or directory. Furthermore, the Subversion
Filesystem is a versioning filesystem, which means that as you make changes to your directory tree,
Subversion remembers what your tree looked like before those changes. And before the previous
changes. And the previous ones. And so on, all the way back through versioning time to (and just beyond) the moment you first started adding things to the filesystem.
All the modifications you make to your tree are done within the context of a Subversion transaction. The
following is a simplified general routine for modifying your filesystem:
Begin a Subversion transaction.
Make your changes (adds, deletes, property modifications, etc.).
Commit your transaction.
Once you have committed your transaction, your filesystem modifications are permanently stored as historical artifacts. Each of these cycles generates a single new revision of your tree, and each revision is
forever accessible as an immutable snapshot of "the way things were."
The Transaction Distraction
The notion of a Subversion transaction, especially given its close proximity the database code in libsvn_fs, can become easily confused with the transaction support provided by the underlying database itself. Both types of transaction exist to provide atomicity and isolation. In other words, transactions give
you the ability to perform a set of actions in an "all or nothing" fashion—either all the actions in the set
complete with success, or they all get treated as if none of them ever happened—and in a way that does
not interfere with other processes acting on the data.
Database transactions generally encompass small operations related specifically to the modification of
data in the database itself (such as changing the contents of a table row). Subversion transactions are
larger in scope, encompassing higher-level operations like making modifications to a set of files and directories which are intended to be stored as the next revision of the filesystem tree. If that isn't confusing
enough, consider this: Subversion uses a database transaction during the creation of a Subversion transaction (so that if the creation of Subversion transaction fails, the database will look as if we had never attempted that creation in the first place)!
The choice of Berkeley DB brought several automatic features that Subversion needed, such as data integrity, atomic writes, recoverability, and hot backups.
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Fortunately for users of the filesystem API, the transaction support provided by the database system itself is hidden almost entirely from view (as should be expected from a properly modularized library
scheme). It is only when you start digging into the implementation of the filesystem itself that such
things become visible (or interesting).
Most of the functionality provided by the filesystem interface comes as an action that occurs on a
filesystem path. That is, from outside of the filesystem, the primary mechanism for describing and accessing the individual revisions of files and directories comes through the use of path strings like /
foo/bar, just as if you were addressing files and directories through your favorite shell program. You
add new files and directories by passing their paths-to-be to the right API functions. You query for information about them by the same mechanism.
Unlike most filesystems, though, a path alone is not enough information to identify a file or directory in
Subversion. Think of a directory tree as a two-dimensional system, where a node's siblings represent a
sort of left-and-right motion, and descending into subdirectories a downward motion. Figure 7-2 shows a
typical representation of a tree as exactly that.
Figure 8.2. Files and Directories in Two Dimensions
Of course, the Subversion filesystem has a nifty third dimension that most filesystems do not
have—Time! 35 In the filesystem interface, nearly every function that has a path argument also expects a root argument. This svn_fs_root_t argument describes either a revision or a Subversion transaction (which is usually just a revision-to-be), and provides that third-dimensional context needed to understand the difference between /foo/bar in revision 32, and the same path as it exists in revision 98.
Figure 7-3 shows revision history as an added dimension to the Subversion filesystem universe.
We understand that this may come as a shock to sci-fi fans who have long been under the impression that Time was actually the
fourth dimension, and we apologize for any emotional trauma induced by our assertion of a different theory.
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Figure 8.3. Revisioning Time—the Third Dimension!
As we mentioned earlier, the libsvn_fs API looks and feels like any other filesystem, except that it has
this wonderful versioning capability. It was designed to be usable by any program interested in a versioning filesystem. Not coincidentally, Subversion itself is interested in that functionality. But while the
filesystem API should be sufficient for basic file and directory versioning support, Subversion wants
more—and that is where libsvn_repos comes in.
The Subversion repository library (libsvn_repos) is basically a wrapper library around the filesystem
functionality. This library is responsible for creating the repository layout, making sure that the underlying filesystem is initialized, and so on. Libsvn_repos also implements a set of hooks—scripts that are executed by the repository code when certain actions take place. These scripts are useful for notification,
authorization, or whatever purposes the repository administrator desires. This type of functionality, and
other utility provided by the repository library, is not strictly related to implementing a versioning
filesystem, which is why it was placed into its own library.
Developers who wish to use the libsvn_repos API will find that it is not a complete wrapper around the
filesystem interface. That is, only certain major events in the general cycle of filesystem activity are
wrapped by the repository interface. Some of these include the creation and commit of Subversion transactions, and the modification of revision properties. These particular events are wrapped by the repository layer because they have hooks associated with them. In the future, other events may be wrapped by
the repository API. All of the remaining filesystem interaction will continue to occur directly with libsvn_fs API, though.
For example, here is a code segment that illustrates the use of both the repository and filesystem interfaces to create a new revision of the filesystem in which a directory is added. Note that in this example
(and all others throughout this book), the SVN_ERR macro simply checks for a non-successful error return from the function it wraps, and returns that error if it exists.
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Example 8.1. Using the Repository Layer
/* Create a new directory at the path NEW_DIRECTORY in the Subversion
repository located at REPOS_PATH. Perform all memory allocation in
POOL. This function will create a new revision for the addition of
static svn_error_t *
make_new_directory (const char *repos_path,
const char *new_directory,
apr_pool_t *pool)
svn_error_t *err;
svn_repos_t *repos;
svn_fs_t *fs;
svn_revnum_t youngest_rev;
svn_fs_txn_t *txn;
svn_fs_root_t *txn_root;
const char *conflict_str;
/* Open the repository located at REPOS_PATH. */
SVN_ERR (svn_repos_open (&repos, repos_path, pool));
/* Get a pointer to the filesystem object that is stored in
fs = svn_repos_fs (repos);
/* Ask the filesystem to tell us the youngest revision that
currently exists. */
SVN_ERR (svn_fs_youngest_rev (&youngest_rev, fs, pool));
/* Begin a new transaction that is based on YOUNGEST_REV. We are
less likely to have our later commit rejected as conflicting if we
always try to make our changes against a copy of the latest snapshot
of the filesystem tree. */
SVN_ERR (svn_fs_begin_txn (&txn, fs, youngest_rev, pool));
/* Now that we have started a new Subversion transaction, get a root
object that represents that transaction. */
SVN_ERR (svn_fs_txn_root (&txn_root, txn, pool));
/* Create our new directory under the transaction root, at the path
SVN_ERR (svn_fs_make_dir (txn_root, new_directory, pool));
/* Commit the transaction, creating a new revision of the filesystem
which includes our added directory path. */
err = svn_repos_fs_commit_txn (&conflict_str, repos,
&youngest_rev, txn, pool);
if (! err)
/* No error? Excellent! Print a brief report of our success. */
printf ("Directory '%s' was successfully added as new revision "
"'%" SVN_REVNUM_T_FMT "'.\n", new_directory, youngest_rev);
else if (err->apr_err == SVN_ERR_FS_CONFLICT)
/* Uh-oh. Our commit failed as the result of a conflict
(someone else seems to have made changes to the same area
of the filesystem that we tried to modify). Print an error
message. */
printf ("A conflict occurred at path '%s' while attempting "
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"to add directory '%s' to the repository at '%s'.\n",
conflict_str, new_directory, repos_path);
/* Some other error has occurred. Print an error message. */
printf ("An error occurred while attempting to add directory '%s' "
"to the repository at '%s'.\n",
new_directory, repos_path);
/* Return the result of the attempted commit to our caller.
return err;
In the previous code segment, calls were made to both the repository and filesystem interfaces. We
could just as easily have committed the transaction using svn_fs_commit_txn. But the filesystem
API knows nothing about the repository library's hook mechanism. If you want your Subversion repository to automatically perform some set of non-Subversion tasks every time you commit a transaction
(like, for example, sending an email that describes all the changes made in that transaction to your developer mailing list), you need to use the libsvn_repos-wrapped version of that
function—svn_repos_fs_commit_txn. This function will actually first run the "pre-commit"
hook script if one exists, then commit the transaction, and finally will run a "post-commit" hook script.
The hooks provide a special kind of reporting mechanism that does not really belong in the core filesystem library itself. (For more information regarding Subversion's repository hooks, see the section called
“Hook Scripts”.)
The hook mechanism requirement is but one of the reasons for the abstraction of a separate repository library from the rest of the filesystem code. The libsvn_repos API provides several other important utilities to Subversion. These include the abilities to:
create, open, destroy, and perform recovery steps on a Subversion repository and the filesystem included in that repository.
describe the differences between two filesystem trees.
query for the commit log messages associated with all (or some) of the revisions in which a set of
files was modified in the filesystem.
generate a human-readable "dump" of the filesystem, a complete representation of the revisions in
the filesystem.
parse that dump format, loading the dumped revisions into a different Subversion repository.
As Subversion continues to evolve, the repository library will grow with the filesystem library to offer
increased functionality and configurable option support.
Repository Access Layer
If the Subversion Repository Layer is at "the other end of the line", the Repository Access Layer is the
line itself. Charged with marshalling data between the client libraries and the repository, this layer includes the libsvn_ra module loader library, the RA modules themselves (which currently includes libsvn_ra_dav, libsvn_ra_local, and libsvn_ra_svn), and any additional libraries needed by one or more of
those RA modules, such as the mod_dav_svn Apache module with which libsvn_ra_dav communicates
or libsvn_ra_svn's server, svnserve.
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Since Subversion uses URLs to identify its repository resources, the protocol portion of the URL schema
(usually file:, http:, https:, or svn:) is used to determine which RA module will handle the
communications. Each module registers a list of the protocols it knows how to "speak" so that the RA
loader can, at runtime, determine which module to use for the task at hand. You can determine which
RA modules are available to the Subversion command-line client, and what protocols they claim to support, by running svn --version:
$ svn --version
svn, version 0.25.0 (dev build)
compiled Jul 18 2003, 16:25:59
Copyright (C) 2000-2003 CollabNet.
Subversion is open source software, see
The following repository access (RA) modules are available:
* ra_dav : Module for accessing a repository via WebDAV (DeltaV) protocol.
- handles 'http' schema
* ra_local : Module for accessing a repository on local disk.
- handles 'file' schema
* ra_svn : Module for accessing a repository using the svn network protocol.
- handles 'svn' schema
RA-DAV (Repository Access Using HTTP/DAV)
The libsvn_ra_dav library is designed for use by clients that are being run on different machines than the
servers with which they communicating, specifically machines reached using URLs that contain the
http: or https: protocol portions. To understand how this module works, we should first mention a
couple of other key components in this particular configuration of the Repository Access Layer—the
powerful Apache HTTP Server, and the Neon HTTP/WebDAV client library.
Subversion's primary network server is the Apache HTTP Server. Apache is a time-tested, extensible
open-source server process that is ready for serious use. It can sustain a high network load and runs on
many platforms. The Apache server supports a number of different standard authentication protocols,
and can be extended through the use of modules to support many others. It also supports optimizations
like network pipelining and caching. By using Apache as a server, Subversion gets all of these features
for free. And since most firewalls already allow HTTP traffic to pass through, sysadmins typically don't
even have to change their firewall configurations to allow Subversion to work.
Subversion uses HTTP and WebDAV (with DeltaV) to communicate with an Apache server. You can
read more about this in the WebDAV section of this chapter, but in short, WebDAV and DeltaV are extensions to the standard HTTP 1.1 protocol that enable sharing and versioning of files over the web.
Apache 2.0 comes with mod_dav, an Apache module that understands the DAV extensions to HTTP.
Subversion itself supplies mod_dav_svn, though, which is another Apache module that works in conjunction with (really, as a back-end to) mod_dav to provide Subversion's specific implementations of
WebDAV and DeltaV.
When communicating with a repository over HTTP, the RA loader library chooses libsvn_ra_dav as the
proper access module. The Subversion client makes calls into the generic RA interface, and libsvn_ra_dav maps those calls (which embody rather large-scale Subversion actions) to a set of HTTP/
WebDAV requests. Using the Neon library, libsvn_ra_dav transmits those requests to the Apache server.
Apache receives these requests (exactly as it does generic HTTP requests that your web browser might
make), notices that the requests are directed at a URL that is configured as a DAV location (using the
Location directive in httpd.conf), and hands the request off to its own mod_dav module. When
properly configured, mod_dav knows to use Subversion's mod_dav_svn for any filesystem-related
needs, as opposed to the generic mod_dav_fs that comes with Apache. So ultimately, the client is communicating with mod_dav_svn, which binds directly to the Subversion Repository Layer.
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That was a simplified description of the actual exchanges taking place, though. For example, the Subversion repository might be protected by Apache's authorization directives. This could result in initial attempts to communicate with the repository being rejected by Apache on authorization grounds. At this
point, libsvn_ra_dav gets back the notice from Apache that insufficient identification was supplied, and
calls back into the Client Layer to get some updated authentication data. If the data is supplied correctly,
and the user has the permissions that Apache seeks, libsvn_ra_dav's next automatic attempt at performing the original operation will be granted, and all will be well. If sufficient authentication information
cannot be supplied, the request will ultimately fail, and the client will report the failure to the user.
By using Neon and Apache, Subversion gets free functionality in several other complex areas, too. For
example, if Neon finds the OpenSSL libraries, it allows the Subversion client to attempt to use SSLencrypted communications with the Apache server (whose own mod_ssl can "speak the language").
Also, both Neon itself and Apache's mod_deflate can understand the "deflate" algorithm (the same used
by the PKZIP and gzip programs), so requests can be sent in smaller, compressed chunks across the
wire. Other complex features that Subversion hopes to support in the future include the ability to automatically handle server-specified redirects (for example, when a repository has been moved to a new
canonical URL) and taking advantage of HTTP pipelining.
RA-SVN (Proprietary Protocol Repository Access)
In addition to the standard HTTP/WebDAV protocol, Subversion also provides an RA implementation
that uses a proprietary protocol. The libsvn_ra_svn module implements its own network socket connectivity, and communicates with a stand-alone server—the svnserve program—on the machine that
hosts the repository. Clients access the repository using the svn:// schema.
This RA implementation lacks most of the advantages of Apache mentioned in the previous section;
however, it may be appealing to some sysadmins nonetheless. It is dramatically easier to configure and
run; setting up an svnserve process is nearly instantaneous. It is also much smaller (in terms of lines
of code) than Apache, making it much easier to audit, for security reasons or otherwise. Furthermore,
some sysadmins may already have an SSH security infrastructure in place, and want Subversion to use
it. Clients using ra_svn can easily tunnel the protocol over SSH.
RA-Local (Direct Repository Access)
Not all communications with a Subversion repository require a powerhouse server process and a network layer. For users who simply wish to access the repositories on their local disk, they may do so using file: URLs and the functionality provided by libsvn_ra_local. This RA module binds directly
with the repository and filesystem libraries, so no network communication is required at all.
Subversion requires the server name included as part of the file: URL be either localhost or
empty, and that there be no port specification. In other words, your URLs should look like either
file://localhost/path/to/repos or file:///path/to/repos.
Also, be aware that Subversion's file: URLs cannot be used in a regular web browser the way typical
file: URLs can. When you attempt to view a file: URL in a regular web browser, it reads and displays the contents of the file at that location by examining the filesystem directly. However, Subversion's resources exist in a virtual filesystem (see the section called “Repository Layer”), and your
browser will not understand how to read that filesystem.
Your RA Library Here
For those who wish to access a Subversion repository using still another protocol, that is precisely why
the Repository Access Layer is modularized! Developers can simply write a new library that implements
the RA interface on one side and communicates with the repository on the other. Your new library can
use existing network protocols, or you can invent your own. You could use inter-process communication
(IPC) calls, or—let's get crazy, shall we?—you could even implement an email-based protocol. Subversion supplies the APIs; you supply the creativity.
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Client Layer
On the client side, the Subversion working copy is where all the action takes place. The bulk of functionality implemented by the client-side libraries exists for the sole purpose of managing working
copies—directories full of files and other subdirectories which serve as a sort of local, editable "reflection" of one or more repository locations—and propagating changes to and from the Repository Access
Subversion's working copy library, libsvn_wc, is directly responsible for managing the data in the working copies. To accomplish this, the library stores administrative information about each working copy
directory within a special subdirectory. This subdirectory, named .svn is present in each working copy
directory and contains various other files and directories which record state and provide a private
workspace for administrative action. For those familiar with CVS, this .svn subdirectory is similar in
purpose to the CVS administrative directories found in CVS working copies. For more information about
the .svn administrative area, see the section called “Inside the Working Copy Administration Area”in
this chapter.
The Subversion client library, libsvn_client, has the broadest responsibility; its job is to mingle the functionality of the working copy library with that of the Repository Access Layer, and then to provide the
highest-level API to any application that wishes to perform general revision control actions. For example, the function svn_client_checkout takes a URL as an argument. It passes this URL to the RA
layer and opens an authenticated session with a particular repository. It then asks the repository for a
certain tree, and sends this tree into the working copy library, which then writes a full working copy to
disk (.svn directories and all).
The client library is designed to be used by any application. While the Subversion source code includes
a standard command-line client, it should be very easy to write any number of GUI clients on top of the
client library. New GUIs (or any new client, really) for Subversion need not be clunky wrappers around
the included command-line client—they have full access via the libsvn_client API to same functionality,
data, and callback mechanisms that the command-line client uses.
Binding Directly—A Word About Correctness
Why should your GUI program bind directly with a libsvn_client instead of acting as a wrapper around a
command-line program? Besides simply being more efficient, this can address potential correctness issues as well. A command-line program (like the one supplied with Subversion) that binds to the client library needs to effectively translate feedback and requested data bits from C types to some form of human-readable output. This type of translation can be lossy. That is, the program may not display all of
the information harvested from the API, or may combine bits of information for compact representation.
If you wrap such a command-line program with yet another program, the second program has access
only to already-interpreted (and as we mentioned, likely incomplete) information, which it must again
translate into its representation format. With each layer of wrapping, the integrity of the original data is
potentially tainted more and more, much like the result of making a copy of a copy (of a copy …) of a
favorite audio or video cassette.
Using the APIs
Developing applications against the Subversion library APIs is fairly straightforward. All of the public
header files live in the subversion/include directory of the source tree. These headers are copied
into your system locations when you build and install Subversion itself from source. These headers represent the entirety of the functions and types meant to be accessible by users of the Subversion libraries.
The first thing you might notice is that Subversion's datatypes and functions are namespace protected.
Every public Subversion symbol name begins with "svn_", followed by a short code for the library in
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which the symbol is defined (such as "wc", "client", "fs", etc.), followed by a single underscore
() and then the rest of the symbol name. Semi-public functions (used among source files of a given library but not by code outside that library, and found inside the library directories themselves) differ
from this naming scheme in that instead of a single underscore after the library code, they use a double
underscore ("__"). Functions that are private to a given source file have no special prefixing, and are
declared static. Of course, a compiler isn't interested in these naming conventions, but they definitely
help to clarify the scope of a given function or datatype.
The Apache Portable Runtime Library
Along with Subversion's own datatype, you will see many references to datatypes that begin with
—symbols from the Apache Portable Runtime (APR) library. APR is Apache's portability library, originally carved out of its server code as an attempt to separate the OS-specific bits from the OSindependent portions of the code. The result was a library that provides a generic API for performing operations that differ mildly—or wildly—from OS to OS. While Apache HTTP Server was obviously the
first user of the APR library, the Subversion developers immediately recognized the value of using APR
as well. This means that there are practically no OS-specific code portions in Subversion itself. Also, it
means that the Subversion client compiles and runs anywhere that the server does. Currently this list includes all flavors of Unix, Win32, BeOS, OS/2, and Mac OS X.
In addition to providing consistent implementations of system calls that differ across operating systems,
36 APR gives Subversion immediate access to many custom datatypes, such as dynamic arrays and hash
tables. Subversion uses these types extensively throughout the codebase. But perhaps the most pervasive
APR datatype, found in nearly every Subversion API prototype, is the apr_pool_t—the APR memory
pool. Subversion uses pools internally for all its memory allocation needs (unless an external library requires a different memory management schema for data passed through its API), 37 and while a person
coding against the Subversion APIs is not required to do the same, they are required to provide pools to
the API functions that need them. This means that users of the Subversion API must also link against
APR, must call apr_initialize() to initialize the APR subsystem, and then must acquire a pool
for use with Subversion API calls. See the section called “Programming with Memory Pools” for more
URL and Path Requirements
With remote version control operation as the whole point of Subversion's existence, it makes sense that
some attention has been paid to internationalization (i18n) support. After all, while "remote" might mean
"across the office", it could just as well mean "across the globe." To facilitate this, all of Subversion's
public interfaces that accept path arguments expect those paths to be canonicalized, and encoded in
UTF-8. This means, for example, that any new client binary that drives the libsvn_client interface needs
to first convert paths from the locale-specific encoding to UTF-8 before passing those paths to the Subversion libraries, and then re-convert any resultant output paths from Subversion back into the locale's
encoding before using those paths for non-Subversion purposes. Fortunately, Subversion provides a
suite of functions (see subversion/include/svn_utf.h) that can be used by any program to do
these conversions.
Also, Subversion APIs require all URL parameters to be properly URI-encoded. So, instead of passing
file:///home/username/My File.txt as the URL of a file named My File.txt, you need
to pass file:///home/username/My%20File.txt. Again, Subversion supplies helper functions that your application can use—svn_path_uri_encode and svn_path_uri_decode, for
URI encoding and decoding, respectively.
Using Languages Other than C and C++
If you are interested in using the Subversion libraries in conjunction with something other than a C program—say a Python script or Java application—Subversion has some initial support for this via the Sim36
Subversion uses ANSI system calls and datatypes as much as possible.
Neon and Berkeley DB are examples of such libraries.
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plified Wrapper and Interface Generator (SWIG). The SWIG bindings for Subversion are located in
subversion/bindings/swig and are slowly maturing into a usable state. These bindings allow
you to call Subversion API functions indirectly, using wrappers that translate the datatypes native to
your scripting language into the datatypes needed by Subversion's C libraries.
There is an obvious benefit to accessing the Subversion APIs via a language binding—simplicity. Generally speaking, languages such as Python and Perl are much more flexible and easy to use than C or
C++. The sort of high-level datatypes and context-driven type checking provided by these languages are
often better at handling information that comes from users. As you know, only a human can botch up the
input to a program as well as they do, and the scripting-type language simply handle that misinformation
more gracefully. Of course, often that flexibility comes at the cost of performance. That is why using a
tightly-optimized, C-based interface and library suite, combined with a powerful, flexible binding language is so appealing.
Let's look at an example that uses Subversion's Python SWIG bindings. Our example will do the same
thing as our last example. Note the difference in size and complexity of the function this time!
Example 8.2. Using the Repository Layer with Python
from svn import fs
import os.path
def crawl_filesystem_dir (root, directory, pool):
"""Recursively crawl DIRECTORY under ROOT in the filesystem, and return
a list of all the paths at or below DIRECTORY. Use POOL for all
# Get the directory entries for DIRECTORY.
entries = fs.dir_entries(root, directory, pool)
# Initialize our returned list with the directory path itself.
paths = [directory]
# Loop over the entries
names = entries.keys()
for name in names:
# Calculate the entry's full path.
full_path = os.path.join(basepath, name)
# If the entry is a directory, recurse. The recursion will return
# a list with the entry and all its children, which we will add to
# our running list of paths.
if fs.is_dir(fsroot, full_path, pool):
subpaths = crawl_filesystem_dir(root, full_path, pool)
# Else, it is a file, so add the entry's full path to the FILES list.
return paths
An implementation in C of the previous example would stretch on quite a bit longer. The same routine
in C would need to pay close attention to memory usage, and need to use custom datatypes for representing the hash of entries and the list of paths. Python has hashes and lists (called "dictionaries" and "sequences", respectively) as built-in datatypes, and provides a wonderful selection of methods for operating on those types. And since Python uses reference counting and garbage collection, users of the lan139
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guage don't have to bother themselves with allocating and freeing memory.
In the previous section of this chapter, we mentioned the libsvn_client interface, and how it exists
for the sole purpose of simplifying the process of writing a Subversion client. The following is a brief
example of how that library can be accessed via the SWIG bindings. In just a few lines of Python, you
can check out a fully functional Subversion working copy!
Example 8.3. A Simple Script to Check Out a Working Copy.
#!/usr/bin/env python
import sys
from svn import util, _util, _client
def usage():
print "Usage: " + sys.argv[0] + " URL PATH\n"
def run(url, path):
# Initialize APR and get a POOL.
pool = util.svn_pool_create(None)
# Checkout the HEAD of URL into PATH (silently)
_client.svn_client_checkout(None, None, url, path, -1, 1, None, pool)
# Cleanup our POOL, and shut down APR.
if __name__ == '__main__':
if len(sys.argv) != 3:
run(sys.argv[1], sys.argv[2])
Currently, it is Subversion's Python bindings that are the most complete. Some attention is also being
given to the Java bindings. Once you have the SWIG interface files properly configured, generation of
the specific wrappers for all the supported SWIG languages (which currently includes versions of C#,
Guile, Java, Mzscheme, OCaml, Perl, PHP, Python, Ruby, and Tcl) should theoretically be trivial. Still,
some extra programming is required to compensate for complex APIs that SWIG needs some help generalizing. For more information on SWIG itself, see the project's website at
Inside the Working Copy Administration Area
As we mentioned earlier, each directory of a Subversion working copy contains a special subdirectory
called .svn which houses administrative data about that working copy directory. Subversion uses the
information in .svn to keep track of things like:
Which repository location(s) are represented by the files and subdirectories in the working copy directory.
What revision of each of those files and directories are currently present in the working copy.
Any user-defined properties that might be attached to those files and directories.
Pristine (un-edited) copies of the working copy files.
Developer Information
While there are several other bits of data stored in the .svn directory, we will examine only a couple of
the most important items.
The Entries File
Perhaps the single most important file in the .svn directory is the entries file. The entries file is an
XML document which contains the bulk of the administrative information about a versioned resource in
a working copy directory. It is this one file which tracks the repository URLs, pristine revision, file
checksums, pristine text and property timestamps, scheduling and conflict state information, last-known
commit information (author, revision, timestamp), local copy history—practically everything that a Subversion client is interested in knowing about a versioned (or to-be-versioned) resource!
Comparing the Administrative Areas of Subversion and CVS
A glance inside the typical .svn directory turns up a bit more than what CVS maintains in its CVS administrative directories. The entries file contains XML which describes the current state of the working copy directory, and basically serves the purposes of CVS's Entries, Root, and Repository
files combined.
The following is an example of an actual entries file:
Example 8.4. Contents of a Typical .svn/entries File
<?xml version="1.0" encoding="utf-8"?>
Developer Information
As you can see, the entries file is essentially a list of entries. Each entry tag represents one of three
things: the working copy directory itself (noted by having its name attribute set to
"svn:this-dir"), a file in that working copy directory (noted by having its kind attribute set to ),
or a subdirectory in that working copy (kind here is set to "dir"). The files and subdirectories whose
entries are stored in this file are either already under version control, or (as in the case of the file named
zeta above) are scheduled to be added to version control when the user next commits this working
copy directory's changes. Each entry has a unique name, and each entry has a node kind.
Developers should be aware of some special rules that Subversion uses when reading and writing its
entries files. While each entry has a revision and URL associated with it, note that not every entry
tag in the sample file has explicit revision or url attributes attached to it. Subversion allows entries
to not explicitly store those two attributes when their values are the same as (in the revision case) or
trivially calculable from 38 (in the url case) the data stored in the "svn:this-dir" entry. Note also
that for subdirectory entries, Subversion stores only the crucial attributes—name, kind, url, revision, and
schedule. In an effort to reduce duplicated information, Subversion dictates that the method for determining the full set of information about a subdirectory is to traverse down into that subdirectory, and
read the "svn:this-dir" entry from its own .svn/entries file. However, a reference to the
subdirectory is kept in its parent's entries file, with enough information to permit basic versioning
operations in the event that the subdirectory itself is actually missing from disk.
Pristine Copies and Property Files
As mentioned before, the .svn directory also holds the pristine "text-base" versions of files. Those can
be found in .svn/text-base. The benefits of these pristine copies are multiple—network-free
checks for local modifications and "diff" reporting, network-free reversion of modified or missing files,
smaller transmission of changes to the server—but comes at the cost of having each versioned file stored
at least twice on disk. These days, this seems to be a negligible penalty for most files. However, the situation gets uglier as the size of your versioned files grows. Some attention is being given to making the
presence of the "text-base" an option. Ironically though, it is as your versioned files' sizes get larger that
the existence of the "text-base" becomes more crucial—who wants to transmit a huge file across a network just because they want to commit a tiny change to it?
Similar in purpose to the "text-base" files are the property files and their pristine "prop-base" copies, located in .svn/props and .svn/prop-base respectively. Since directories can have properties,
too, there are also .svn/dir-props and .svn/dir-prop-base files. Each of these property files
("working" and "base" versions) uses a simple "hash-on-disk" file format for storing the property names
and values.
WebDAV ("Web-based Distributed Authoring and Versioning") is an extension of the standard HTTP
protocol designed to make the web into a read/write medium, instead of the basically read-only medium
that exists today. The theory is that directories and files can be shared—as both readable and writable
objects—over the web. RFCs 2518 and 3253 describe the WebDAV/DeltaV extensions to HTTP, and
are available (along with a lot of other useful information) at
A number of operating system file browsers are already able to mount networked directories using WebDAV. On Win32, the Windows Explorer can browse what it calls "WebFolders" (which are just WebDAV-ready network locations) as if they were regular shared folders. Mac OS X also has this capability,
That is, the URL for the entry is the same as the concatenation of the parent directory's URL and the entry's name.
Developer Information
as do the Nautilus and Konqueror browsers (under GNOME and KDE, respectively).
How does all of this apply to Subversion? The mod_dav_svn Apache module uses HTTP, extended by
WebDAV and DeltaV, as its primary network protocol. Rather than implementing a new proprietary
protocol, the original Subversion designers decided to simply map the versioning concepts and actions
used by Subversion onto the concepts exposed by RFCs 2518 and 3253. 39
For a more thorough discussion of WebDAV, how it works, and how Subversion uses it, see
Appendix C, WebDAV and Autoversioning. Among other things, that appendix discusses the degree to
which Subversion adheres to the generic WebDAV specification, and how that affects interoperability
with generic WebDAV clients.
Programming with Memory Pools
Almost every developer who has used the C programming language has at some point sighed at the
daunting task of managing memory usage. Allocating enough memory to use, keeping track of those allocations, freeing the memory when you no longer need it—these tasks can be quite complex. And of
course, failure to do those things properly can result in a program that crashes itself, or worse, crashes
the computer. Fortunately, the APR library that Subversion depends on for portability provides the
apr_pool_t type, which represents a "pool" of memory.
A memory pool is an abstract representation of a chunk of memory allocated for use by a program.
Rather than requesting memory directly from the OS using the standard malloc() and friends, programs that link against APR can simply request that a pool of memory be created (using the
apr_pool_create() function). APR will allocate a moderately sized chunk of memory from the
OS, and that memory will be instantly available for use by the program. Any time the program needs
some of the pool memory, it uses one of the APR pool API functions, like apr_palloc(), which returns a generic memory location from the pool. The program can keep requesting bits and pieces of
memory from the pool, and APR will keep granting the requests. Pools will automatically grow in size
to accommodate programs that request more memory than the original pool contained, until of course
there is no more memory available on the system.
Now, if this were the end of the pool story, it would hardly have merited special attention. Fortunately,
that's not the case. Pools can not only be created; they can also be cleared and destroyed, using
apr_pool_clear() and apr_pool_destroy() respectively. This gives developers the flexibility to allocate several—or several thousand— things from the pool, and then clean up all of that memory
with a single function call! Further, pools have hierarchy. You can make "subpools" of any previously
created pool. When you clear a pool, all of its subpools are destroyed; if you destroy a pool, it and its
subpools are destroyed.
Before we go further, developers should be aware that they probably will not find many calls to the APR
pool functions we just mentioned in the Subversion source code. APR pools offer some extensibility
mechanisms, like the ability to have custom "user data" attached to the pool, and mechanisms for registering cleanup functions that get called when the pool is destroyed. Subversion makes use of these extensions in a somewhat non-trivial way. So, Subversion supplies (and most of its code uses) the wrapper
functions svn_pool_create(), svn_pool_clear(), and svn_pool_destroy().
While pools are helpful for basic memory management, the pool construct really shines in looping and
recursive scenarios. Since loops are often unbounded in their iterations, and recursions in their depth,
memory consumption in these areas of the code can become unpredictable. Fortunately, using nested
memory pools can be a great way to easily manage these potentially hairy situations. The following example demonstrates the basic use of nested pools in a situation that is fairly common—recursively
crawling a directory tree, doing some task to each thing in the tree.
As it turns out, Subversion has more recently evolved a proprietary protocol anyway, implemented by the libsvn_ra_svn module.
Developer Information
Example 8.5. Effective Pool Usage
/* Recursively crawl over DIRECTORY, adding the paths of all its file
children to the FILES array, and doing some task to each path
encountered. Use POOL for the all temporary allocations, and store
the hash paths in the same pool as the hash itself is allocated in.
static apr_status_t
crawl_dir (apr_array_header_t *files,
const char *directory,
apr_pool_t *pool)
apr_pool_t *hash_pool = files->pool; /* array pool */
apr_pool_t *subpool = svn_pool_create (pool); /* iteration pool */
apr_dir_t *dir;
apr_finfo_t finfo;
apr_status_t apr_err;
apr_int32_t flags = APR_FINFO_TYPE | APR_FINFO_NAME;
apr_err = apr_dir_open (&dir, directory, pool);
if (apr_err)
return apr_err;
/* Loop over the directory entries, clearing the subpool at the top of
each iteration. */
for (apr_err = apr_dir_read (&finfo, flags, dir);
apr_err == APR_SUCCESS;
apr_err = apr_dir_read (&finfo, flags, dir))
const char *child_path;
/* Skip entries for "this dir" ('.') and its parent ('..'). */
if (finfo.filetype == APR_DIR)
if ([0] == '.'
&& ([1] == '\0'
|| ([1] == '.' &&[2] == '\0')))
/* Build CHILD_PATH from DIRECTORY and */
child_path = svn_path_join (directory,, subpool);
/* Do some task to this encountered path. */
do_some_task (child_path, subpool);
/* Handle subdirectories by recursing into them, passing SUBPOOL
as the pool for temporary allocations. */
if (finfo.filetype == APR_DIR)
apr_err = crawl_dir (files, child_path, subpool);
if (apr_err)
return apr_err;
/* Handle files by adding their paths to the FILES array. */
else if (finfo.filetype == APR_REG)
/* Copy the file's path into the FILES array's pool. */
child_path = apr_pstrdup (hash_pool, child_path);
/* Add the path to the array.
Developer Information
(*((const char **) apr_array_push (files))) = child_path;
/* Clear the per-iteration SUBPOOL.
svn_pool_clear (subpool);
/* Check that the loop exited cleanly. */
if (apr_err)
return apr_err;
/* Yes, it exited cleanly, so close the dir. */
apr_err = apr_dir_close (dir);
if (apr_err)
return apr_err;
/* Destroy SUBPOOL. */
svn_pool_destroy (subpool);
The previous example demonstrates effective pool usage in both looping and recursive situations. Each
recursion begins by making a subpool of the pool passed to the function. This subpool is used for the
looping region, and cleared with each iteration. The result is memory usage is roughly proportional to
the depth of the recursion, not to total number of file and directories present as children of the top-level
directory. When the first call to this recursive function finally finishes, there is actually very little data
stored in the pool that was passed to it. Now imagine the extra complexity that would be present if this
function had to alloc() and free() every single piece of data used!
Pools might not be ideal for every application, but they are extremely useful in Subversion. As a Subversion developer, you'll need to grow comfortable with pools and how to wield them correctly. Memory
usage bugs and bloating can be difficult to diagnose and fix regardless of the API, but the pool construct
provided by APR has proven a tremendously convenient, time-saving bit of functionality.
Contributing to Subversion
The official source of information about the Subversion project is, of course, the project's website at There you can find information about getting access to the
source code and participating on the discussion lists. The Subversion community always welcomes new
members. If you are interested in participating in this community by contributing changes to the source
code, here are some hints on how to get started.
Join the Community
The first step in community participation is to find a way to stay on top of the latest happenings. To do
this most effectively, you will want to subscribe to the main developer discussion list
(<>). By following these lists even loosely, you will have access to
important design discussions, be able to see actual changes to Subversion source code as they occur, and
be able to witness peer reviews of those changes and proposed changes. These email based discussion
lists are the primary communication media for Subversion development. See the Mailing Lists section of
the website for other Subversion-related lists you might be interested in.
But how do you know what needs to be done? It is quite common for a programmer to have the greatest
intentions of helping out with the development, yet be unable to find a good starting point. After all, not
many folks come to the community having already decided on a particular itch they would like to
Developer Information
scratch. But by watching the developer discussion lists, you might see mentions of existing bugs or feature requests fly by that particularly interest you. Also, a great place to look for outstanding, unclaimed
tasks is the Issue Tracking database on the Subversion website. There you will find the current list of
known bugs and feature requests. If you want to start with something small, look for issues marked as
Get the Source Code
To edit the code, you need to have the code. This means you need to check out a working copy from the
public Subversion source repository. As straightforward as that might sound, the task can be slightly
tricky. Because Subversion's source code is versioned using Subversion itself, you actually need to "bootstrap" by getting a working Subversion client via some other method. The most common methods include downloading the latest binary distribution (if such is available for your platform), or downloading
the latest source tarball and building your own Subversion client. If you build from source, make sure to
read the INSTALL file in the top level of the source tree for instructions.
After you have a working Subversion client, you are now poised to checkout a working copy of the Subversion source repository from 40
$ svn checkout subversion
A build.conf
The above command will checkout the bleeding-edge, latest version of the Subversion source code into
a subdirectory named subversion in your current working directory. Obviously, you can adjust that
last argument as you see fit. Regardless of what you call the new working copy directory, though, after
this operation completes, you will now have the Subversion source code. Of course, you will still need
to fetch a few helper libraries (apr, apr-util, etc.)—see the INSTALL file in the top level of the working
copy for details.
Become Familiar with Community Policies
Now that you have a working copy containing the latest Subversion source code, you will most certainly
want to take a cruise through the HACKING file in that working copy's top-level directory. The HACKING file contains general instructions for contributing to Subversion, including how to properly format
your source code for consistency with the rest of the codebase, how to describe your proposed changes
with an effective change log message, how to test your changes, and so on. Commit privileges on the
Subversion source repository are earned—a government by meritocracy. 41 The HACKING file is an invaluable resource when it comes to making sure that your proposed changes earn the praises they deserve without being rejected on technicalities.
Make and Test Your Changes
With the code and community policy understanding in hand, you are ready to make your changes. It is
best to try to make smaller but related sets of changes, even tackling larger tasks in stages, instead of
making huge, sweeping modifications. Your proposed changes will be easier to understand (and therefore easier to review) if you disturb the fewest lines of code possible to accomplish your task properly.
After making each set of proposed changes, your Subversion tree should be in a state in which the soft40
Note that the URL checked out in the example above ends not with svn, but with a subdirectory thereof called trunk. See our
discussion of Subversion's branching and tagging model for the reasoning behind this.
While this may superficially appear as some sort of elitism, this "earn your commit privileges" notion is about
efficiency—whether it costs more in time and effort to review and apply someone else's changes that are likely to be safe and useful, versus the potential costs of undoing changes that are dangerous.
Developer Information
ware compiles with no warnings.
Subversion has a fairly thorough 42 regression test suite, and your proposed changes are expected to not
cause any of those tests to fail. By running make check (in Unix) from the top of the source tree, you
can sanity-check your changes. The fastest way to get your code contributions rejected (other than failing to supply a good log message) is to submit changes that cause failure in the test suite.
In the best-case scenario, you will have actually added appropriate tests to that test suite which verify
that your proposed changes actually work as expected. In fact, sometimes the best contribution a person
can make is solely the addition of new tests. You can write regression tests for functionality that currently works in Subversion as a way to protect against future changes that might trigger failure in those
areas. Also, you can write new tests that demonstrate known failures. For this purpose, the Subversion
test suite allows you to specify that a given test is expected to fail (called an XFAIL), and so long as
Subversion fails in the way that was expected, a test result of XFAIL itself is considered a success. Ultimately, the better the test suite, the less time wasted on diagnosing potentially obscure regression bugs.
Donate Your Changes
After making your modifications to the source code, compose a clear and concise log message to describe those changes and the reasons for them. Then, send an email to the developers list containing your
log message and the output of svn diff (from the top of your Subversion working copy). If the community members consider your changes acceptable, someone who has commit privileges (permission to
make new revisions in the Subversion source repository) will add your changes to the public source code
tree. Recall that permission to directly commit changes to the repository is granted on merit—if you
demonstrate comprehension of Subversion, programming competency, and a "team spirit", you will
likely be awarded that permission.
You might want to grab some popcorn. "Thorough", in this instance, translates to somewhere around thirty minutes of noninteractive machine churn.
Chapter 9.
This chapter is intended to be a complete reference to using Subversion. This includes the command line
client (svn) and all its subcommands, as well as the repository administration programs (svnadmin and
svnlook) and their respective subcommands.
The Subversion Command Line Client: svn
To use the command line client, you type svn, the subcommand you wish to use 43, and any switches or
targets that you wish to operate on—there is no specific order that the subcommand and the switches
must appear in. For example, all of the following are valid ways to use svn status:
$ svn -v status
$ svn status -v
$ svn status -v myfile
You can find many more examples of how to use most client commands in Chapter 3, Guided Tour and
commands for managing properties in the section called “Properties”
svn Switches
While Subversion has different switches for its subcommands, all switches are global—that is, each
switch is guaranteed to mean the same thing regardless of the subcommand you use it with. For example, --verbose (-v) always means “verbose output”, regardless of the subcommand you use it with.
Enable auto-props, overriding the enable-auto-props directive in the
config file.
--config-dir DIR
Instructs Subversion to read configuration information from the specified directory instead of the default location (.subversion in the user's home
--diff-cmd CMD
Specifies an external program to use to show differences between files.
When svn diff is invoked, it uses Subversion's internal diff engine, which
provides unified diffs by default. If you want to use an external diff program, use --diff-cmd. You can pass switches to the diff program with
the --extensions switch (more on that later in this section).
--diff3-cmd CMD
Specifies an external program to use to merge files.
Goes through all the motions of running a command, but makes no actual
changes—either on disk or in the repository.
--editor-cmd CMD
Specifies an external program to use to edit a log message or a property
--encoding ENC
Tells Subversion that your commit message is encoded in the charset provided. The default is your operating system's native locale, and you should
specify the encoding if your commit message is in any other encoding.
Yes, yes, you don't need a subcommand to use the --version switch, but we'll get to that in just a minute.
Subversion Complete Reference
--extensions (-x) "ARGS"
Specifies an argument or arguments that Subversion should pass to an external diff command when providing differences between files. If you wish to
pass multiple arguments, you must enclose all of them in quotes (for example, svn diff --diff-cmd /usr/bin/diff -x "-b -E"). This switch can only be
used if you also pass the --diff-cmd switch.
--file (-F) FILENAME Uses the contents of the file passed as an argument to this switch for the
specified subcommand.
Forces a particular command or operation to run. There are some operations
that Subversion will prevent you from doing in normal usage, but you can
pass the force switch to tell Subversion “I know what I'm doing as well as
the possible repercussions of doing it, so let me at 'em”. This switch is the
programmatic equivalent of doing your own electrical work with the power
on—if you don't know what you're doing, you're likely to get a nasty shock.
Forces a suspicious parameter passed to the --message (-m) or --file
(-F) options to be accepted as valid. By default, Subversion will produce an
error if parameters to these options look like they might instead be targets of
the subcommand. For example, if you pass a versioned file's path to the -file (-F) option, Subversion will assume you've made a mistake, that the
path was instead intended as the target of the operation, and that you simply
failed to provide some other—unversioned—file as the source of your log
message. To assert your intent and override these types of errors, pass the -force-log option to commands that accept log messages.
--help (-h or -?)
If used with one or more subcommands, shows the built-in help text for each
subcommand. If used alone, it displays the general client help text.
Ignore ancestry when calculating differences (rely on path contents alone).
Prints output in a format suitable for concatenation.
--message (-m) MESSAGE
Indicates that you will specify a commit message on the command line, following this switch. For example:
$ svn commit -m "They don't make Sunday."
--new ARG
Uses ARG as the newer target.
Prevents caching of authentication information (e.g. username and password) in the Subversion administrative directories.
Disable auto-props, overriding the enable-auto-props directive in the
config file.
Prevents Subversion from printing differences for deleted files. The default
behavior when you remove a file is for svn diff to print the same differences
that you would see if you had left the file but removed all the content.
Shows files in the status listing that would normally be omitted since they
match a pattern in the svn:ignore property. See the section called “Config”
for more information.
In the case of an authentication failure, or insufficient credentials, prevents
prompting for credentials (e.g. username or password). This is useful if
Subversion Complete Reference
you're running Subversion inside of an automated script and it's more appropriate to have Subversion fail than to prompt for more information.
--non-recursive (-N)Stops a subcommand from recursing into subdirectories. Most subcommands recurse by default, but some subcommands—usually those that have
the potential to remove or undo your local modifications—do not.
Pay attention to ancestry when calculating differences.
--old ARG
Uses ARG as the older target.
--password PASS
Indicates that you are providing your password for authentication on the
command line—otherwise, if it is needed, Subversion will prompt you for it.
--quiet (-q)
Requests that the client print only essential information while performing an
--recursive (-R)
Makes a subcommand recurse into subdirectories. Most subcommands recurse by default.
--relocate FROM TO [PATH...]
Used with the svn switch subcommand, changes the location of the repository that your working copy references. This is useful if the location of your
repository changes and you have an existing working copy that you'd like to
continue to use. See svn switch for an example.
--revision (-r) REV
Indicates that you're going to supply a revision (or range of revisions) for a
particular operation. You can provide revision numbers, revision keywords
or dates (in curly braces), as arguments to the revision switch. If you wish to
provide a range of revisions, you can provide two revisions separated by a
colon. For example:
See the section called “Revision Keywords” for more information.
Operates on a revision property instead of a Subversion property specific to
a file or directory. This switch requires that you also pass a revision with the
--revision (-r) switch. See the section called “Unversioned Properties”
for more details on unversioned properties.
--show-updates (-u) Causes the client to display information about which files in your working
copy are out-of-date. This doesn't actually update any of your files—it just
shows you which files will be updated if you run svn update .
Causes a Subversion subcommand which is traversing the history of a versioned resource to stop harvesting that historical information when a
copy—that is, a location in history where that resource was copied from another location in the repository—is encountered.
Causes Subversion to use strict semantics, a notion which is rather vague
unless talking about specific subcommands.
--targets FILENAME Tells Subversion to get the list of files that you wish to operate on from the
Subversion Complete Reference
filename you provide instead of listing all the files on the command line.
--username NAME
Indicates that you are providing your username for authentication on the
command line—otherwise, if it is needed, Subversion will prompt you for it.
--verbose (-v)
Requests that the client print out as much information as it can while running any subcommand. This may result in Subversion printing out additional
fields, detailed information about every file, or additional information regarding its actions.
Prints the client version info. This information not only includes the version
number of the client, but also a listing of all repository access modules that
the client can use to access a Subversion repository.
Prints output in XML format.
svn Subcommands
Subversion Complete Reference
svn add -- Adds files and directories
svn add
svn add PATH...
Adds files and directories to your working copy and schedules them for addition to the repository. They
will be uploaded and added to the repository on your next commit. If you add something and change
your mind before committing, you can unschedule the addition using svn revert.
Alternate Names
Working Copy
--targets FILENAME
--non-recursive (-N)
--quiet (-q)
--config-dir DIR
To add a file to your working copy:
$ svn add foo.c
When adding a directory, the default behavior of svn add is to recurse:
$ svn add testdir
Subversion Complete Reference
You can add a directory without adding its contents:
$ svn add --non-recursive otherdir
Subversion Complete Reference
svn blame -- Shows author and revision information in-line for the specified files or URLs.
svn blame
svn blame TARGET...
Shows author and revision information in-line for the specified files or URLs. Each line of text is annotated at the beginning with the author (username) and the revision number for the last change to that
Alternate Names
praise, annotate, ann
Accesses Repository
--revision (-r) REV
--username USER
--password PASS
--config-dir DIR
If you want to see blame annotated source for readme.txt in your test repository:
$ svn blame
sally This is a README file.
harry You should read this.
Subversion Complete Reference
svn cat -- Outputs the contents of the specified files or URLs.
svn cat
svn cat TARGET...
Outputs the contents of the specified files or URLs. For listing the contents of directories, see svn list.
Alternate Names
Accesses Repository
--revision (-r) REV
--username USER
--password PASS
--config-dir DIR
If you want to view readme.txt in your repository without checking it out:
$ svn cat
This is a README file.
You should read this.
If your working copy is out of date (or you have local modifications) and you want to see the
HEAD revision of a file in your working copy, svn cat will automatically fetch the HEAD revision when you give it a path:
$ cat foo.c
Subversion Complete Reference
This file is in my local working copy
and has changes that I've made.
$ svn cat foo.c
Latest revision fresh from the repository!
Subversion Complete Reference
svn checkout -- Checks out a working copy from a repository.
svn checkout
svn checkout URL... [PATH]
Checks out a working copy from a repository. If PATH is omitted, the basename of the URL will be used
as the destination. If multiple URLs are given each will be checked out into a sub-directory of PATH,
with the name of the sub-directory being the basename of the URL.
Alternate Names
Creates a working copy.
Accesses Repository
--revision (-r) REV
--quiet (-q)
--non-recursive (-N)
--username USER
--password PASS
--config-dir DIR
Check out a working copy into a directory called 'mine':
$ svn checkout file:///tmp/repos/test mine
A mine/a
A mine/b
Checked out revision 2.
$ ls
Check out 2 different directories into two separate working copies:
Subversion Complete Reference
$ svn checkout file:///tmp/repos/test
A test/a
A test/b
Checked out revision 2.
A quiz/l
A quiz/m
Checked out revision 2.
$ ls
quiz test
Check out 2 different directories into two separate working copies, but place both into a directory called
'working copies':
$ svn checkout file:///tmp/repos/test
A working-copies/test/a
A working-copies/test/b
Checked out revision 2.
A working-copies/quiz/l
A working-copies/quiz/m
Checked out revision 2.
$ ls
file:///tmp/repos/quiz working-copies
If you interrupt a checkout (or something else interrupts your checkout like loss of connectivity, etc.),
you can restart it either by issuing the identical checkout command again, or by updating the incomplete
working copy:
$ svn checkout file:///tmp/repos/test test
A test/a
A test/b
svn: The operation was interrupted
svn: caught SIGINT
$ svn checkout file:///tmp/repos/test test
A test/c
A test/d
svn: The operation was interrupted
svn: caught SIGINT
$ cd test
$ svn update
A test/e
A test/f
Updated to revision 3.
Subversion Complete Reference
svn cleanup -- Recursively clean up the working copy.
svn cleanup
svn cleanup [PATH...]
Recursively clean up the working copy, removing locks resuming unfinished operations. If you ever get
a “working copy locked” error, run this command to remove stale locks and get your working copy into
a usable state again. See Appendix B, Troubleshooting.
If, for some reason, an svn update fails due to a problem running an external diff program (e.g. user input or network failure), pass the --diff3-cmd to allow cleanup to complete any merging with your
external diff program. You can also specify any configuration directory with the --config-dir
switch, but you should need these switches extremely infrequently.
Alternate Names
Working copy
Accesses Repository
--diff3-cmd CMD
--config-dir DIR
Well, there's not much to the examples here as svn cleanup generates no output. If you pass no PATH,
'.' is used.
$ svn cleanup
$ svn cleanup /path/to/working-copy
Subversion Complete Reference
svn commit -- Send changes from your working copy to the repository.
svn commit
svn commit [PATH...]
Send changes from your working copy to the repository. If you do not supply a log message with your
commit by using either the --file or --message switch, svn will launch your editor for you to compose a commit message. See the editor-cmd section in the section called “Config”.
If you begin a commit and Subversion launches your editor to compose the commit message,
you can still abort without committing your changes. If you want to cancel your commit, just
quit your editor without saving your commit message and Subversion will prompt you to either
abort the commit, continue with no message, or edit the message again.
Alternate Names
ci (short for “check in” not “co”, which is short for “checkout”)
Working copy, repository
Accesses Repository
--message (-m) TEXT
--file (-F) FILE
--quiet (-q)
--non-recursive (-N)
--targets FILENAME
--username USER
--password PASS
--encoding ENC
--config-dir DIR
Commit a simple modification to a file with the commit message on the command line and an implicit
target of your current directory (“.”):
Subversion Complete Reference
$ svn commit -m "added howto section."
Transmitting file data .
Committed revision 3.
Commit a modification to the file foo.c (explicitly specified on the command line) with the commit
message in a file named msg:
$ svn commit -F msg foo.c
Transmitting file data .
Committed revision 5.
If you want to use a file that's under version control for your commit message with --file, you need
to pass the --force-log switch:
$ svn commit --file file_under_vc.txt foo.c
svn: The log message file is under version control
svn: Log message file is a versioned file; use `--force-log' to override.
$ svn commit --force-log --file file_under_vc.txt foo.c
Transmitting file data .
Committed revision 6.
To commit a file scheduled for deletion:
svn commit -m "removed file 'c'."
Committed revision 7.
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svn copy -- Copy a file or directory in a working copy or in the repository.
svn copy
svn copy SRC DST
Copy a file in a working copy or in the repository. SRC and DST can each be either a working copy
(WC) path or URL:
WC -> WC
Copy and schedule an item for addition (with history).
Immediately commit a copy of WC to URL.
Check out URL into WC, and schedule it for addition.
Complete server-side copy. This is usually used to branch and tag.
You can only copy files within a single repository. Subversion does not support crossrepository copying.
Alternate Names
Repository if destination is a URL.
Working copy if destination is a WC path.
Accesses Repository
If source or destination is in the repository, or if needed to look up the source revision number.
--message (-m) TEXT
--file (-F) FILE
--revision (-r) REV
--quiet (-q)
--username USER
--password PASS
--editor-cmd EDITOR
Subversion Complete Reference
--encoding ENC
--config-dir DIR
Copy an item within your working copy (just schedules the copy—nothing goes into the repository until
you commit):
$ svn copy foo.txt bar.txt
$ svn status
A +
Copy an item in your working copy to a URL in the repository (an immediate commit, so you must supply a commit message):
$ svn copy near.txt file:///tmp/repos/test/far-away.txt -m "Remote copy."
Committed revision 8.
Copy an item from the repository to your working copy (just schedules the copy—nothing goes into the
repository until you commit):
This is the recommended way to resurrect a dead file in your repository!
$ svn copy file:///tmp/repos/test/far-away near-here
And finally, copying between two URLs:
$ svn copy file:///tmp/repos/test/far-away file:///tmp/repos/test/over-there -m "re
Committed revision 9.
This is the easiest way to 'tag' a revision in your repository—just svn copy that revision
(usually HEAD) into your tags directory.
$ svn copy file:///tmp/repos/test/trunk file:///tmp/repos/test/tags/0.6.32-prerelea
Committed revision 12.
Subversion Complete Reference
And don't worry if you forgot to tag—you can always specify an older revision and tag anytime:
$ svn copy -r 11 file:///tmp/repos/test/trunk file:///tmp/repos/test/tags/0.6.32-pr
Committed revision 13.
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svn delete -- Delete an item from a working copy or the repository.
svn delete
svn delete PATH...
svn delete URL...
Items specified by PATH are scheduled for deletion upon the next commit. Files (and directories that
have not been committed) are immediately removed from the working copy. The command will not remove any unversioned or modified items; use the --force switch to override this behavior.
Items specified by URL are deleted from the repository via an immediate commit. Multiple URLs are
committed atomically.
Alternate Names
del, remove, rm
Working copy if operating on files, Repository if operating on URLs
Accesses Repository
Only if operating on URLs
--message (-m) TEXT
--file (-F) FILE
--quiet (-q)
--targets FILENAME
--username USER
--password PASS
--editor-cmd EDITOR
--encoding ENC
--config-dir DIR
Using svn to delete a file from your working copy merely schedules it to be deleted. When you commit,
the file is deleted in the repository.
Subversion Complete Reference
$ svn delete myfile
$ svn commit -m "Deleted file 'myfile'."
Transmitting file data .
Committed revision 14.
Deleting a URL, however, is immediate, so you have to supply a log message:
$ svn delete -m "Deleting file 'yourfile'" file:///tmp/repos/test/yourfile
Committed revision 15.
Here's an example of how to force deletion of a file that has local mods:
$ svn delete over-there
svn: Attempting restricted operation for modified resource
svn: Use --force to override this restriction
svn: 'over-there' has local modifications
$ svn delete --force over-there
Subversion Complete Reference
svn diff -- Display the differences between two paths.
svn diff
svn diff [-r N[:M]] [TARGET...]
svn diff URL1[@N] URL2[@M]
Display the differences between two paths. Each TARGET can be either a working copy path or URL. If
no TARGET is specified, a value of '.' is assumed.
If TARGET is a URL, then revs N and M must be given via the --revision.
If TARGET is a working copy path, then the --revision switch means:
--revision N:M
The server compares TARGET@N and TARGET@M.
--revision N
The client compares TARGET@N against working copy.
(no --revision)
The client compares base and working copies of TARGET.
If the alternate syntax is used, the server compares URL1 and URL2 at revisions N and M respectively.
If either N or M are omitted, a value of HEAD is assumed.
By default, svn diff ignores the ancestry of files and merely compares the contents of the two files being
compared. If you use --notice-ancestry, the ancestry of the paths in question will be taken into
consideration when comparing revisions (that is, if you run svn diff on two files with identical contents
but different ancestry you will see the entire contents of the file as having been removed and added
Alternate Names
Accesses Repository
For obtaining differences against anything but BASE revision in your working copy
--revision (-r) REV
Subversion Complete Reference
--extensions (-x) "ARGS"
--non-recursive (-N)
--diff-cmd CMD
--username USER
--password PASS
--config-dir DIR
Compare BASE and your working copy (one of the most popular uses of svn diff):
$ svn diff COMMITTERS
--- COMMITTERS (revision 4404)
+++ COMMITTERS (working copy)
See how your working copy's modifications compare against an older revision:
$ svn diff -r 3900 COMMITTERS
--- COMMITTERS (revision 3900)
+++ COMMITTERS (working copy)
Compare revision 3000 to revision 3500 using '@' syntax:
$ svn diff http://svn.collab.
--- COMMITTERS (revision 3000)
+++ COMMITTERS (revision 3500)
Compare revision 3000 to revision 3500 using range notation (you only pass the one URL in this case):
$ svn diff -r 3000:3500
--- COMMITTERS (revision 3000)
+++ COMMITTERS (revision 3500)
If you have a working copy, you can obtain the differences without typing in the long URLs:
$ svn diff -r 3000:3500 COMMITTERS
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--- COMMITTERS (revision 3000)
+++ COMMITTERS (revision 3500)
Use --diff-cmd CMD -x to pass arguments directly to the external diff program
svn diff --diff-cmd /usr/bin/diff -x "-i -b" COMMITTERS
> This is a test
Subversion Complete Reference
svn export -- Exports a clean directory tree.
svn export
svn export [-r REV] URL [PATH]
svn export PATH1 PATH2
The first form exports a clean directory tree from the repository specified by URL, at revision REV if it
is given, otherwise at HEAD, into PATH. If PATH is omitted, the last component of the URL is used for
the local directory name.
The second form exports a clean directory tree from the working copy specified by PATH1 into PATH2.
All local changes will be preserved, but files not under version control will not be copied.
Alternate Names
Local disk
Accesses Repository
Only if exporting from a URL
--revision (-r) REV
--quiet (-q)
--username USER
--password PASS
--config-dir DIR
Export from your working copy (doesn't print every file and directory):
$ svn export a-wc my-export
Export complete.
Subversion Complete Reference
Export directly from the repository (prints every file and directory):
$ svn export file:///tmp/repos my-export
A my-export/test
A my-export/quiz
Exported revision 15.
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svn help -- Help!
svn help
svn help [SUBCOMMAND...]
This is your best friend when you're using Subversion and this book isn't within reach!
Alternate Names
?, h
Accesses Repository
--quiet (-q)
Subversion Complete Reference
svn import -- Recursively commit a copy of PATH to URL.
svn import
svn import [PATH] URL
Recursively commit a copy of PATH to URL. If PATH is omitted '.' is assumed. Parent directories are
created in the repository as necessary.
Alternate Names
Accesses Repository
--message (-m) TEXT
--file (-F) FILE
--quiet (-q)
--non-recursive (-N)
--username USER
--password PASS
--editor-cmd EDITOR
--encoding ENC
--config-dir DIR
This imports the local directory 'myproj' into the root of your repository:
$ svn import -m "New import" myproj
Transmitting file data .........
Committed revision 16.
Subversion Complete Reference
This imports the local directory 'myproj' into 'trunk/vendors' in your repository. The directory 'trunk/
vendors' need not exist before you import into it—svn import will recursively create directories for you:
$ svn import -m "New import" myproj \
Transmitting file data .........
Committed revision 19.
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svn info -- Print information about PATHs.
svn info
svn info [PATH...]
Print information about paths in your working copy, including:
Node Kind
Last Changed Author
Last Changed Revision
Last Changed Date
Text Last Updated
Properties Last Updated
Alternate Names
Accesses Repository
--targets FILENAME
--recursive (-R)
--config-dir DIR
Subversion Complete Reference
svn info will show you all the useful information that it has for items in your working copy. It will show
information for files:
$ svn info foo.c
Path: foo.c
Name: foo.c
Revision: 4417
Node Kind: file
Schedule: normal
Last Changed Author: sally
Last Changed Rev: 20
Last Changed Date: 2003-01-13 16:43:13 -0600 (Mon, 13 Jan 2003)
Text Last Updated: 2003-01-16 21:18:16 -0600 (Thu, 16 Jan 2003)
Properties Last Updated: 2003-01-13 21:50:19 -0600 (Mon, 13 Jan 2003)
Checksum: /3L38YwzhT93BWvgpdF6Zw==
It will also show information for directories:
$ svn info vendors
Path: trunk
Revision: 19
Node Kind: directory
Schedule: normal
Last Changed Author: harry
Last Changed Rev: 19
Last Changed Date: 2003-01-16 23:21:19 -0600 (Thu, 16 Jan 2003)
Subversion Complete Reference
svn list -- List directory entries in the repository.
svn list
svn list [TARGET...]
List each TARGET file and the contents of each TARGET directory as they exist in the repository. If
TARGET is a working copy path, the corresponding repository URL will be used.
The default TARGET is '.', meaning the repository URL of the current working copy directory.
With --verbose, the following fields show the status of the item:
Revision number of the last commit
Author of the last commit
Size (in bytes)
Date and time of the last commit
Alternate Names
Accesses Repository
--revision (-r) REV
--verbose (-v)
--recursive (-R)
--username USER
--password PASS
--config-dir DIR
Subversion Complete Reference
svn list is most useful if you want to see what files a repository has without downloading a working
$ svn list
Like UNIX ls, you can also pass the --verbose switch for additional information:
svn list --verbose file:///tmp/repos
16 sally
28361 Jan 16 23:18 README.txt
27 sally
0 Jan 18 15:27 INSTALL
24 harry
Jan 18 11:27 examples/
For further details, see the section called “svn list”.
Subversion Complete Reference
svn log -- Displays commit log messages.
svn log
svn log [PATH]
svn log URL [PATH...]
The default target is the path of your current directory. If no arguments are supplied, svn log shows the
log messages for all files and directories inside of (and including) the current working directory of your
working copy. You can refine the results by specifying a path, one or more revisions, or any combination of the two. The default revision range for a local path is BASE:1.
If you specify a URL alone, then it prints log messages for everything that the URL contains. If you add
paths past the URL, only messages for those paths under that URL will be printed. The default revision
range for a URL is HEAD:1.
With --verbose, svn log will also print all affected paths with each log message. With --quiet,
svn log will not print the log message body itself (this is compatible with --verbose).
Each log message is printed just once, even if more than one of the affected paths for that revision were
explicitly requested. Logs follow copy history by default. Use --stop-on-copy to disable this behavior,
which can be useful for determining branch points.
Alternate Names
Accesses Repository
--revision (-r) REV
--quiet (-q)
--verbose (-v)
--targets FILENAME
--username USER
--password PASS
Subversion Complete Reference
--config-dir DIR
You can see the log messages for all the paths that changed in your working copy by running svn log
from the top:
$ svn log
-----------------------------------------------------------------------r20 | harry | 2003-01-17 22:56:19 -0600 (Fri, 17 Jan 2003) | 1 line
-----------------------------------------------------------------------r17 | sally | 2003-01-16 23:21:19 -0600 (Thu, 16 Jan 2003) | 2 lines
Examine all log messages for a particular file in your working copy:
$ svn log foo.c
-----------------------------------------------------------------------r32 | sally | 2003-01-13 16:43:13 -0600 (Mon, 13 Jan 2003) | 1 line
Added defines.
-----------------------------------------------------------------------r28 | sally | 2003-01-07 21:48:33 -0600 (Tue, 07 Jan 2003) | 3 lines
If you don't have a working copy handy, you can log a URL:
$ svn log
-----------------------------------------------------------------------r32 | sally | 2003-01-13 16:43:13 -0600 (Mon, 13 Jan 2003) | 1 line
Added defines.
-----------------------------------------------------------------------r28 | sally | 2003-01-07 21:48:33 -0600 (Tue, 07 Jan 2003) | 3 lines
If you want several distinct paths underneath the same URL, you can use the URL [PATH...] syntax.
$ svn log foo.c bar.c
-----------------------------------------------------------------------r32 | sally | 2003-01-13 16:43:13 -0600 (Mon, 13 Jan 2003) | 1 line
Added defines.
-----------------------------------------------------------------------r31 | harry | 2003-01-10 12:25:08 -0600 (Fri, 10 Jan 2003) | 1 line
Added new file bar.c
-----------------------------------------------------------------------r28 | sally | 2003-01-07 21:48:33 -0600 (Tue, 07 Jan 2003) | 3 lines
Subversion Complete Reference
That is the same as explicitly placing both URLs on the command line:
$ svn log \
When you're concatenating the results of multiple calls to the log command, you may want to use the -incremental switch. svn log normally prints out a dashed line at the beginning of a log message,
after each subsequent log message, and following the final log message. If you ran svn log on a range of
two revisions, you would get this:
$ svn log -r 14:15
-----------------------------------------------------------------------r14 | ...
-----------------------------------------------------------------------r15 | ...
However, if you wanted to gather 2 non-sequential log messages into a file, you might do something like
$ svn log -r 14 > mylog
$ svn log -r 19 >> mylog
$ svn log -r 27 >> mylog
$ cat mylog
-----------------------------------------------------------------------r14 | ...
----------------------------------------------------------------------------------------------------------------------------------------------r19 | ...
----------------------------------------------------------------------------------------------------------------------------------------------r27 | ...
You can avoid the clutter of the double dashed lines in your output by using the incremental switch:
$ svn log --incremental -r 14 > mylog
$ svn log --incremental -r 19 >> mylog
$ svn log --incremental -r 27 >> mylog
$ cat mylog
-----------------------------------------------------------------------r14 | ...
-----------------------------------------------------------------------r19 | ...
Subversion Complete Reference
-----------------------------------------------------------------------r27 | ...
The --incremental switch provides similar output control when using the --xml switch.
If you run svn log on a specific path and provide a specific revision and get no output at all
$ svn log -r 20
That just means that the path was not modified in that revision. If you log from the top of the
repository, or know the file that changed in that revision, you can specify it explicitly:
$ svn log -r 20 touched.txt
-----------------------------------------------------------------------r20 | sally | 2003-01-17 22:56:19 -0600 (Fri, 17 Jan 2003) | 1 line
Made a change.
Subversion Complete Reference
svn merge -- Apply the differences between two sources to a working copy path.
svn merge
svn merge sourceURL1[@N] sourceURL2[@M] [WCPATH]
svn merge -r N:M SOURCE [PATH]
In the first form, the source URLs are specified at revisions N and M. These are the two sources to be
compared. The revisions default to HEAD if omitted.
In the second form, SOURCE can be a URL or working copy item, in which case the corresponding
URL is used. This URL, at revisions N and M, defines the two sources to be compared.
WCPATH is the working copy path that will receive the changes. If WCPATH is omitted, a default
value of '.' is assumed, unless the sources have identical basenames that match a file within '.': in which
case, the differences will be applied to that file.
Unlike svn diff, the merge command takes the ancestry of a file into consideration when performing a
merge operation. This is very important when you're merging changes from one branch into another and
you've renamed a file on one branch but not the other.
Alternate Names
Working copy
Accesses Repository
Only if working with URLs
--revision (-r) REV
--non-recursive (-N)
--quiet (-q)
--diff3-cmd CMD
--username USER
--password PASS
--config-dir DIR
Subversion Complete Reference
Merge a branch back into the trunk (assuming that you have a working copy of the trunk):
$ svn merge \
U myproj/tiny.txt
U myproj/thhgttg.txt
U myproj/win.txt
U myproj/flo.txt
If you branched at revision 23, and you want to merge changes on trunk into your branch, you could do
this from inside the working copy of your branch:
$ svn merge -r 23:30 file:///tmp/repos/trunk/vendors
U myproj/thhgttg.txt
To merge changes to a single file:
$ cd myproj
$ svn merge -r 30:31 thhgttg.txt
U thhgttg.txt
Subversion Complete Reference
svn mkdir -- Create a new directory under version control.
svn mkdir
svn mkdir PATH...
svn mkdir URL...
Create a directory with a name given by the final component of the PATH or URL. A directory specified
by a working copy PATH is scheduled for addition in the working copy. A directory specified by a URL
is created in the repository via an immediate commit. Multiple directory URLs are committed atomically. In both cases all the intermediate directories must already exist.
Alternate Names
Working copy, repository if operating on a URL
Accesses Repository
Only if operating on a URL
--message (-m) TEXT
--file (-F) FILE
--quiet (-q)
--username USER
--password PASS
--editor-cmd EDITOR
--encoding ENC
--config-dir DIR
Create a directory in your working copy:
$ svn mkdir newdir
Subversion Complete Reference
Create one in the repository (instant commit, so a log message is required):
$ svn mkdir -m "Making a new dir."
Committed revision 26.
Subversion Complete Reference
svn move -- Move a file or directory.
svn move
svn move SRC DST
This command moves a file or directory in your working copy or in the repository.
This command is equivalent to an svn copy followed by svn delete.
Subversion does not support moving between working copies and URLs. In addition, you can
only move files within a single repository—Subversion does not support cross-repository moving.
WC -> WC
Move and schedule a file or directory for addition (with history).
Complete server-side rename.
Alternate Names
mv, rename, ren
Working copy, repository if operating on a URL
Accesses Repository
Only if operating on a URL
--message (-m) TEXT
--file (-F) FILE
--revision (-r) REV
--quiet (-q)
--username USER
--password PASS
--editor-cmd EDITOR
--encoding ENC
Subversion Complete Reference
--config-dir DIR
Move a file in your working copy:
$ svn move foo.c bar.c
Move a file in the repository (an immediate commit, so it requires a commit message):
$ svn move -m "Move a file" \
Committed revision 27.
Subversion Complete Reference
svn propdel -- Remove a property from an item.
svn propdel
svn propdel PROPNAME [PATH...]
svn propdel PROPNAME --revprop -r REV [URL]
This removes properties from files, directories, or revisions. The first form removes versioned properties
in working copy, while the second removes unversioned remote properties on a repository revision.
Alternate Names
pdel, pd
Working copy, repository only if operating on a URL
Accesses Repository
Only if operating on a URL
--quiet (-q)
--recursive (-R)
--revision (-r) REV
--username USER
--password PASS
--config-dir DIR
Delete a property from a file in your working copy
$ svn propdel svn:mime-type some-script
property `svn:mime-type' deleted from 'some-script'.
Delete a revision property:
Subversion Complete Reference
$ svn propdel --revprop -r 26 release-date
property `release-date' deleted from repository revision '26'
Subversion Complete Reference
svn propedit -- Edit the property of one or more items under version control.
svn propedit
svn propedit PROPNAME PATH...
svn propedit PROPNAME --revprop -r REV [URL]
Edits one or more properties using your favorite editor. The first form edits versioned properties in your
working copy, while the second edits unversioned remote properties on a repository revision.
Alternate Names
pedit, pe
Working copy, repository only if operating on a URL
Accesses Repository
Only if operating on a URL
--revision (-r) REV
--username USER
--password PASS
--encoding ENC
--editor-cmd EDITOR
--config-dir DIR
svn propedit makes it easy to modify properties that have multiple values:
$ svn propedit svn:keywords foo.c
<svn will launch your favorite editor here, with a buffer open
containing the current contents of the svn:keywords property. You
can add multiple values to a property easily here by entering one
value per line.>
Set new value for property `svn:keywords' on `foo.c'
Subversion Complete Reference
svn propget -- Prints the value of a property.
svn propget
svn propget PROPNAME [PATH...]
svn propget PROPNAME --revprop -r REV [URL]
Prints the value of a property on files, directories, or revisions. The first form prints the versioned property of an item or items in your working copy, while the second prints unversioned remote property on a
repository revision. See the section called “Properties” for more information on properties.
Alternate Names
pget, pg
Working copy, repository only if operating on a URL
Accesses Repository
Only if operating on a URL
--recursive (-R)
--revision (-r) REV
--username USER
--password PASS
--config-dir DIR
Examine a property of a file in your working copy:
$ svn propget svn:keywords foo.c
Subversion Complete Reference
The same goes for a revision property:
$ svn propget svn:log --revprop -r 20
Began journal.
Subversion Complete Reference
svn proplist -- Lists all properties.
svn proplist
svn proplist [PATH...]
svn proplist --revprop -r REV [URL]
Lists all properties on files, directories, or revisions. The first form lists versioned properties in working
copy, while the second lists unversioned remote properties on a repository revision.
Alternate Names
plist, pl
Working copy, repository only if operating on a URL
Accesses Repository
Only if operating on a URL
--verbose (-v)
--recursive (-R)
--revision (-r) REV
--quiet (-q)
--username USER
--password PASS
--config-dir DIR
You can use proplist to see the properties on an item in your working copy:
$ svn proplist foo.c
Properties on 'foo.c':
Subversion Complete Reference
But with the --verbose flag, svn proplist is extremely handy as it also shows you the values for the
$ svn proplist --verbose foo.c
Properties on 'foo.c':
svn:mime-type : text/plain
svn:keywords : Author Date Rev
owner : sally
Subversion Complete Reference
svn propset -- Set PROPNAME to PROPVAL on files, directories, or revisions.
svn propset
svn propset PROPNAME --revprop -r REV [PROPVAL | -F VALFILE] [URL]
Set PROPNAME to PROPVAL on files, directories, or revisions. The first example creates a versioned,
local property change in the working copy, and the second creates an unversioned, remote property
change on a repository revision.
Subversion has a number of “special” properties that affect its behavior. See the section called
“Special properties” for more on these properties.
Alternate Names
pset, ps
Working copy, repository only if operating on a URL
Accesses Repository
Only if operating on a URL
--file (-F) FILE
--quiet (-q)
--revision (-r) REV
--targets FILENAME
--recursive (-R)
--username USER
--password PASS
--encoding ENC
--config-dir DIR
Subversion Complete Reference
Set the mimetype on a file:
$ svn propset svn:mime-type image/jpeg foo.jpg
property `svn:mime-type' set on 'foo.jpg'
On a UNIX system, if you want a file to have the executable permission set:
$ svn propset svn:executable ON somescript
property `svn:executable' set on 'somescript'
Perhaps you have an internal policy to set certain properties for the benefit of your coworkers:
$ svn propset owner sally foo.c
property `owner' set on 'foo.c'
If you made a mistake in a log message for a particular revision and want to change it, use --revprop
and set svn:log to the new log message:
$ svn propset --revprop -r 25 svn:log "Journaled about trip to New York."
property `svn:log' set on repository revision '25'
Or, if you don't have a working copy, you can provide a URL.
$ svn propset --revprop -r 26 svn:log "Document nap."
property `svn:log' set on repository revision '25'
Lastly, you can tell propset to take its input from a file. You could even use this to set the contents of a
property to something binary:
$ svn propset owner-pic -F sally.jpg moo.c
property `owner-pic' set on 'moo.c'
By default, you cannot modify revision properties in a Subversion repository. Your repository
administrator must explicitly enable revision property modifications by creating a hook named
'pre-revprop-change'. See the section called “Hook Scripts” for more information on hook
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svn resolved -- Remove “conflicted” state on working copy files or directories.
svn resolved
svn resolved PATH...
Remove “conflicted” state on working copy files or directories. This routine does not semantically resolve conflict markers; it merely removes conflict-related artifact files and allows PATH to be committed again; that is, it tells Subversion that the conflicts have been “resolved”. See the section called Re“solve Conflicts (Merging Others' Changes)” for an in-depth look at resolving conflicts.
Alternate Names
Working copy
Accesses Repository
--targets FILENAME
--recursive (-R)
--quiet (-q)
--config-dir DIR
If you get a conflict on an update, your working copy will sprout three new files:
$ svn update
C foo.c
Updated to revision 31.
$ ls
Once you've resolved the conflict and foo.c is ready to be committed, run svn resolved to let your
working copy know you've taken care of everything.
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You can just remove the conflict files and commit, but svn resolved fixes up some bookkeeping data in the working copy administrative area in addition to removing the conflict files, so
we recommend that you use this command.
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svn revert -- Undo all local edits.
svn revert
svn revert PATH...
Reverts any local changes to a file or directory and resolves any conflicted states. svn revert will not
only revert the contents of an item in your working copy, but also any property changes. Finally, you
can use it to undo any scheduling operations that you may have done (e.g. files scheduled for addition or
deletion can be “unscheduled”).
Alternate Names
Working copy
Accesses Repository
--targets FILENAME
--recursive (-R)
--quiet (-q)
--config-dir DIR
Discard changes to a file:
$ svn revert foo.c
Reverted foo.c
If you want to revert a whole directory of files, use the --recursive flag:
$ svn revert --recursive .
Reverted newdir/afile
Reverted foo.c
Reverted bar.txt
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Lastly, you can undo any scheduling operations:
$ svn add mistake.txt whoops
$ svn revert mistake.txt whoops
Reverted mistake.txt
Reverted whoops
$ svn status
If you provide no targets to svn revert, it will do nothing—to protect you from accidentally
losing changes in your working copy, svn revert requires you to provide at least one target.
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svn status -- Print the status of working copy files and directories.
svn status
svn status [PATH...]
Print the status of working copy files and directories. With no arguments, it prints only locally modified
items (no repository access). With --show-updates, add working revision and server out-of-date information. With --verbose, print full revision information on every item.
The first five columns in the output are each one character wide, and each column gives you information
about different aspects of each working copy item.
The first column indicates that an item was added, deleted, or otherwise changed.
No modifications.
Item is scheduled for Addition.
Item is scheduled for Deletion.
Item has been modified.
Item is in conflict with updates received from the repository.
Item is being ignored (e.g. with the svn:ignore property)
Item is not under version control.
Item is missing (e.g. you moved or deleted it without using svn). This also indicates that a directory is incomplete (a checkout or update was interrupted).
Item is versioned as a directory, but has been replaced by a file, or vice versa
The second column tells the status of a file's or directory's properties.
No modifications.
Properties for this item have been modified.
Properties for this item are in conflict with property updates received from the repository.
The third column is populated only if the working copy directory is locked.
Item is not locked.
Item is locked.
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The fourth column is populated only if the item is scheduled for addition-with-history.
No history scheduled with commit.
History scheduled with commit.
The fifth column is populated only if the item is switched relative to its parent (see the section called
“Switching a Working Copy”).
Item is child of its parent directory.
Item is switched.
The out-of-date information appears in the eighth column (only if you pass the --show-updates
The item in your working copy is up-to-date.
A newer revision of the item exists on the server.
The remaining fields are variable width and delimited by spaces. The working revision is the next field
if the --show-updates or --verbose switches are passed.
If the --verbose switch is passed, the last committed revision and last committed author are displayed next.
The working copy path is always the final field, so it can include spaces.
Alternate Names
stat, st
Accesses Repository
Only if using --show-updates
--show-updates (-u)
--verbose (-v)
--non-recursive (-N)
--quiet (-q)
--username USER
--password PASS
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This is the easiest way to find out what changes you have made to your working copy:
$ svn status wc
A +
If you want to find out what files in your working copy are out-of-date, pass the --show-updates
switch (this will not make any changes to your working copy). Here you can see that wc/foo.c has
changed in the repository since we last updated our working copy:
$ svn status --show-updates wc
A +
Head revision:
--show-updates only places an asterisk next to items that are out of date (that is, items that
will be updated from the repository if you run svn update). --show-updates does not
cause the status listing to reflect the repository's version of the item.
And finally, the most information you can get out of the status subcommand:
$ svn status --show-updates --verbose wc
938 sally
922 harry
A +
687 harry
687 harry
Head revision:
For many more examples of svn status, see the section called “svn status”.
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svn switch -- Update working copy to a different URL.
svn switch
svn switch URL [PATH]
This subcommand updates your working copy to mirror a new URL—usually a URL which shares a
common ancestor with your working copy, although not necessarily. This is the Subversion way to
move a working copy to a new branch. See the section called “Switching a Working Copy” for an indepth look at switching.
Alternate Names
Working copy
Accesses Repository
--revision (-r) REV
--non-recursive (-N)
--quiet (-q)
--diff3-cmd CMD
--username USER
--password PASS
--config-dir DIR
If you're currently inside the directory 'vendors' which was branched to 'vendors-with-fix' and you'd like
to switch your working copy to that branch:
$ svn switch .
U myproj/foo.txt
U myproj/bar.txt
U myproj/baz.c
U myproj/qux.c
Updated to revision 31.
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And to switch back, just provide the URL to the location in the repository from which you originally
checked out your working copy:
$ svn switch .
U myproj/foo.txt
U myproj/bar.txt
U myproj/baz.c
U myproj/qux.c
Updated to revision 31.
You can just switch part of your working copy to a branch if you don't want to switch your entire working copy.
If the location of your repository changes and you have an existing working copy that you'd like to continue to use, you can use svn switch --relocate to change your working copy from one URL to another:
$ svn checkout file:///tmp/repos test
A test/a
A test/b
$ mv repos newlocation
$ cd test/
$ svn update
svn: Couldn't open a repository.
svn: Unable to open an ra_local session to URL
svn: Unable to open repository 'file:///tmp/repos'
$ svn switch --relocate file:///tmp/repos file:///tmp/newlocation .
$ svn update
At revision 3.
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svn update -- Updates your working copy.
svn update
svn update [PATH...]
svn update brings changes from the repository into your working copy. If no revision given, it brings
your working copy up-to-date with the HEAD revision. Otherwise, it synchronizes the working copy to
the revision given by the --revision switch.
For each updated item a line will start with a character reporting the action taken. These characters have
the following meaning:
A Added
D Deleted
U Updated
C Conflict
M Merged
A character in the first column signifies an update to the actual file, while updates to the file's properties
are shown in the second column.
Alternate Names
Working copy
Accesses Repository
--revision (-r) REV
--non-recursive (-N)
--quiet (-q)
--diff3-cmd CMD
--username USER
--password PASS
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--config-dir DIR
Pick up repository changes that have happened since your last update:
$ svn update
A newdir/toggle.c
A newdir/disclose.c
A newdir/launch.c
D newdir/README
Updated to revision 32.
You can also update your working copy to an older revision (Subversion doesn't have the concept of
“sticky” files like CVS does; see Appendix A, Subversion for CVS Users):
svn update -r30
A newdir/README
D newdir/toggle.c
D newdir/disclose.c
D newdir/launch.c
U foo.c
Updated to revision 30.
If you want to examine an older revision of a single file, you may want to use svn cat.
svnadmin is the administrative tool for monitoring and repairing your Subversion repository. For detailed information, see the section called “svnadmin”
Since svnadmin works via direct repository access (and thus can only be used on the machine that holds
the repository), it refers to the repository with a path, not a URL.
svnadmin Switches
Bypass the repository hook system.
Follow copy history when examining a path.
--in-repos-template ARG
Specify a template for the repository structure when creating a new
The “in-repository” templates specify the layout of the repository
itself (which lives in Berkeley DB files inside the db/ directory)
like /trunk, /branches, etc. These templates can be used by an administrator or application to do an initial load of the repository
(without invoking hooks). There is no default; the repository is
built “empty” unless you tell it otherwise.
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Dump a revision only as a diff against the previous revision, instead of the usual fulltext.
--on-disk-template ARG
Specify a template to use for the on-disk structure (i.e. conf/,
hooks/, etc.) of the repository you want to create.
The “on-disk” templates describe the repository directory itself.
Each of the templates have a name, and the “default” on-disk template contains:
The typical usage for the on-disk structures is to predefine the hook
scripts that will be created. For example, you could prepopulate the
post-commit script with a commit mailer and backup script.
Then, each time the administrator creates a new repository, she can
refer to this new template which automagically includes all of the
--revision (-r) ARG
Specify a particular revision to operate on.
svnadmin Subcommands
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svnadmin list-unused-dblogs -- Ask Berkeley DB which log files can be safely deleted.
svnadmin list-unused-dblogs
svnadmin list-unused-dblogs REPOS_PATH
Berkeley DB creates logs of all changes to the repository, which allow it to recover in the face of catastrophe. Over time, the log files accumulate, although most are no longer used and can be deleted to reclaim disk space. See the section called “” for more information.
Remove all unused log files from a repository:
$ svnadmin list-unused-dblogs /path/to/repos
$ svnadmin list-unused-dblogs /path/to/repos | xargs rm
## disk space reclaimed!
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svnadmin create -- Create a new, empty repository at REPOS_PATH.
svnadmin create
svnadmin create REPOS_PATH
Create a new, empty repository at the path provided. If the provided directory does not exist, it will be
created for you.
--on-disk-template arg
--in-repos-template arg
Creating a new repository is just this easy:
$ svnadmin create /usr/local/svn/repos
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svnadmin dump -- Dump the contents of filesystem to stdout.
svnadmin dump
svnadmin dump REPOS_PATH [-r LOWER[:UPPER]] [--incremental]
Dump the contents of filesystem to stdout in a 'dumpfile' portable format, sending feedback to stderr.
Dump revisions LOWER rev through UPPER rev. If no revisions are given, dump all revision trees. If
only LOWER is given, dump that one revision tree. See the section called “Migrating a Repository” for
a practical use.
--revision (-r)
Dump your whole repository:
$ svnadmin dump /usr/local/svn/repos
SVN-fs-dump-format-version: 1
Revision-number: 0
* Dumped revision 0.
Prop-content-length: 56
Content-length: 56
Incrementally dump a single transaction from your repository:
$ svnadmin dump /usr/local/svn/repos -r 21 --incremental
* Dumped revision 21.
SVN-fs-dump-format-version: 1
Revision-number: 21
Prop-content-length: 101
Content-length: 101
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svnadmin help
svnadmin help
svnadmin help [SUBCOMMAND...]
This subcommand is useful when you're trapped on a desert island with neither a net connection nor a
copy of this book.
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svnadmin load -- Read a “dumpfile-formatted” stream from stdin.
svnadmin load
svnadmin load REPOS_PATH
Read a “dumpfile”-formatted stream from stdin, committing new revisions into the repository's filesystem. Send progress feedback to stdout.
This shows the beginning of loading a repository from a backup file (made, of course, with svn dump):
$ svnadmin load /usr/local/svn/restored < repos-backup
<<< Started new txn, based on original revision 1
* adding path : test ... done.
* adding path : test/a ... done.
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svnadmin lstxns -- Print the names of all uncommitted transactions.
svnadmin lstxns
svnadmin lstxns REPOS_PATH
Print the names of all uncommitted transactions. See the section called “Repository Cleanup” for information on how uncommitted transactions are created and what you should do with them.
List all outstanding transactions in a repository.
$ svnadmin lstxns /usr/local/svn/repos/
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svnadmin recover -- Recovers any lost state in a repository.
svnadmin recover
svnadmin recover REPOS_PATH
Run this command if you get an error indicating that your repository needs to be recovered.
Only run this when you are absolutely certain you're the only process accessing the
repository—it requires exclusive access. See the section called “Managing Disk Space” for a
detailed explanation of repository recovery.
Recover a hung repository:
$ svnadmin recover /usr/local/svn/repos/
Acquiring exclusive lock on repository db.
Recovery is running, please stand by...
Recovery completed.
The latest repos revision is 34.
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svnadmin rmtxns -- Deletes transactions from a repository.
svnadmin rmtxns
svnadmin rmtxns REPOS_PATH TXN_NAME...
Deletes outstanding transactions from a repository. This is covered in detail in the section called Repos“itory Cleanup”
Remove named transactions:
$ svnadmin rmtxns /usr/local/svn/repos/ 1w 1x
Fortunately, the output of svn lstxns works great as the input for rmtxns:
$ svnadmin rmtxns /usr/local/svn/repos/
`svnadmin lstxns /usr/local/svn/repos/`
Which will remove all uncommitted transactions from your repository.
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svnadmin setlog -- Set the log-message on a revision.
svnadmin setlog
svnadmin setlog REPOS_PATH -r REVISION FILE
Set the log-message on revision REVISION to the contents of FILE.
This is similar to using svn propset --revprop to set the svn:log property on a revision, except that
you can also use the option --bypass-hooks to avoid running any pre- or post-commit hooks, which
is useful if the modification of revision properties has not been enabled in the pre-revprop-change hook.
Revision properties are not under version control, so this command will permanently overwrite
the previous log message.
--revision (-r) ARG
Set the log message for revision 19 to the contents of the file 'msg':
$ svnadmin setlog /usr/local/svn/repos/ -r 19 msg
svnlook is a command-line utility for examining different aspects of a Subversion repository. It does not
make any changes to the repository—it's just used for “peeking”. svnlook is typically used by the repository hooks, but a repository administrator might find it useful for diagnostic purposes.
Since svnlook works via direct repository access (and thus can only be used on the machine that holds
the repository), it refers to the repository with a path, not a URL.
If no revision or transaction is specified, svnlook defaults to the youngest (most recent) revision of the
svnlook Switches
Switches in svnlook are global, just like in svn and svnadmin, however, most switches only apply to
Subversion Complete Reference
one subcommand since the functionality of svnlook is (intentionally) limited in scope.
Prevents svnlook from printing differences for deleted files. The default behavior when a file is deleted in a transaction/revision is to print the same differences that you would see if you had left the file but removed all the content.
--revision (-r)
Specify a particular revision number that you wish to examine.
--transaction (-t)
Specify a particular transaction id that you wish to examine.
Show the filesystem node revision IDs for each path in the filesystem tree.
svnlook Subcommands
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svnlook author -- Prints the author.
svnlook author
svnlook author REPOS_PATH
Prints the author of a revision or transaction in the repository.
--revision (-r)
--transaction (-t)
svnlook author is handy, but not very exciting:
$ svnlook author -r 40 /usr/local/svn/repos
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svnlook cat -- Print the contents of a file.
svnlook cat
Print the contents of a file.
--revision (-r)
--transaction (-t)
This shows the contents of a file in transaction ax8, located at /trunk/README:
$ svnlook cat -t ax8 /usr/local/svn/repos /trunk/README
Subversion, a version control system.
$LastChangedDate: 2003-07-17 10:45:25 -0500 (Thu, 17 Jul 2003) $
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svnlook changed -- Print the paths that were changed.
svnlook changed
svnlook changed REPOS_PATH
Print the paths that were changed in a particular revision or transaction, as well as an “svn update-style”
status letter in the first column: A for added, D for deleted, and U for updated (modified).
--revision (-r)
--transaction (-t)
This shows a list of all the changed files in revision 39 of a test repository:
$ svnlook changed -r 39 /usr/local/svn/repos
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svnlook date -- Print the datestamp.
svnlook date
svnlook date REPOS_PATH
Print the datestamp of a revision or transaction in a repository.
--revision (-r)
--transaction (-t)
This shows the date of revision 40 of a test repository:
$ svnlook date -r 40 /tmp/repos/
2003-02-22 17:44:49 -0600 (Sat, 22 Feb 2003)
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svnlook diff -- Prints differences of changed files and properties.
svnlook diff
svnlook diff REPOS_PATH
Prints GNU-style differences of changed files and properties in a repository.
--revision (-r)
--transaction (-t)
This shows a newly added (empty) file, a deleted file, and a copied file:
$ svnlook diff -r 40 /usr/local/svn/repos/
Copied: egg.txt (from rev 39, trunk/vendors/deli/pickle.txt)
Added: trunk/vendors/deli/soda.txt
Modified: trunk/vendors/deli/sandwich.txt
--- trunk/vendors/deli/sandwich.txt (original)
+++ trunk/vendors/deli/sandwich.txt 2003-02-22 17:45:04.000000000 -0600
@@ -0,0 +1 @@
+Don't forget the mayo!
Deleted: trunk/vendors/deli/chips.txt
Deleted: trunk/vendors/deli/pickle.txt
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svnlook dirs-changed -- Print the directories that were themselves changed.
svnlook dirs-changed
svnlook dirs-changed REPOS_PATH
Print the directories that were themselves changed (property edits) or whose file children were changed.
--revision (-r)
--transaction (-t)
This shows the directories that changed in revision 40 in our sample repository:
$ svnlook dirs-changed -r 40 /usr/local/svn/repos
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svnlook help
svnlook help
Also svnlook -h and svnlook -?.
Displays the help message for svnlook. This command, like its brother svn help, is also your friend,
even though you never call it anymore and forgot to invite it to your last party.
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svnlook history -- Print information about the history of a path in the repository (or the root directory if
no path is supplied).
svnlook history
svnlook history REPOS_PATH
Print information about the history of a path in the repository (or the root directory if no path is supplied).
--revision (-r)
This shows the history output for the path /tags/1.0 as of revision 15 in our sample repository.
$ svnlook history -r 20 /usr/local/svn/repos /tags/1.0 --show-ids
/tags/1.0 <1.2.12>
/branches/1.0-rc2 <1.1.10>
/branches/1.0-rc2 <1.1.x>
/trunk <1.0.q>
/trunk <1.0.o>
/trunk <1.0.k>
/trunk <1.0.g>
/trunk <1.0.e>
/trunk <1.0.b>
/trunk <1.0.9>
/trunk <1.0.7>
/trunk <1.0.6>
/trunk <1.0.3>
/trunk <1.0.2>
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svnlook info -- Print the author, datestamp, log message size, and log message.
svnlook info
svnlook info REPOS_PATH
Print the author, datestamp, log message size, and log message.
--revision (-r)
--transaction (-t)
This shows the info output for revision 40 in our sample repository.
$ svnlook info -r 40 /usr/local/svn/repos
2003-02-22 17:44:49 -0600 (Sat, 22 Feb 2003)
Rearrange lunch.
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svnlook log -- Print the log message.
svnlook log
svnlook log REPOS_PATH
Print the log message.
--revision (-r)
--transaction (-t)
This shows the log output for revision 40 in our sample repository:
$ svnlook log /tmp/repos/
Rearrange lunch.
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svnlook proplist -- Print the names and values of versioned file and directory properties.
svnlook proplist
svnlook proplist REPOS_PATH PATH_IN_REPOS
List the properties of a path in the repository. With -v, show the property values too.
--revision (-r)
--transaction (-t)
--verbose (-v)
This shows the names of properties set on the file /trunk/README in the HEAD revision:
$ svnlook proplist /usr/local/svn/repos /trunk/README
This is the same command as in the previous example, but this time showing the property values as well:
$ svnlook proplist /usr/local/svn/repos /trunk/README
original-author : fitz
svn:mime-type : text/plain
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svnlook tree -- Print the tree
svnlook tree
Print the tree, starting at PATH_IN_REPOS (if supplied, at the root of the tree otherwise), optionally
showing node revision ids.
--revision (-r)
--transaction (-t)
This shows the tree output (with node-IDs) for revision 40 in our sample repository:
$ svnlook tree -r 40 /usr/local/svn/repos --show-ids
/ <0.0.2j>
trunk/ <p.0.2j>
vendors/ <q.0.2j>
deli/ <1g.0.2j>
egg.txt <1i.e.2j>
soda.txt <1k.0.2j>
sandwich.txt <1j.0.2j>
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svnlook youngest -- Print the youngest revision number.
svnlook youngest
svnlook youngest REPOS_PATH
Print the youngest revision number of a repository.
This shows the youngest revision of our sample repository:
$ svnlook youngest /tmp/repos/
Appendix A. Subversion for CVS Users
This appendix is a guide for CVS users new to Subversion. It's essentially a list of differences between
the two systems as “viewed from 10,000 feet”. For each section, we provide backreferences to relevant
chapters when possible.
Although the goal of Subversion is to take over the current and future CVS user base, some new features
and design changes were required to fix certain “broken” behaviors that CVS had. This means that, as a
CVS user, you may need to break habits—ones that you forgot were odd to begin with.
Revision Numbers Are Different Now
In CVS, revision numbers are per-file. This is because CVS uses RCS as a backend; each file has a corresponding RCS file in the repository, and the repository is roughly laid out according to the structure of
your project tree.
In Subversion, the repository looks like a single filesystem. Each commit results in an entirely new
filesystem tree; in essence, the repository is an array of trees. Each of these trees is labeled with a single
revision number. When someone talks about “revision 54”, they're talking about a particular tree (and
indirectly, the way the filesystem looked after the 54th commit).
Technically, it's not valid to talk about “revision 5 of foo.c”. Instead, one would say “foo.c as it appears in revision 5”. Also, be careful when making assumptions about the evolution of a file. In CVS, revisions 5 and 6 of foo.c are always different. In Subversion, it's most likely that foo.c did not
change between revisions 5 and 6.
For more details on this topic, see the section called “Revisions”.
Directory Versions
Subversion tracks tree structures, not just file contents. It's one of the biggest reasons Subversion was
written to replace CVS.
Here's what this means to you, as a former CVS user:
The svn add and svn rm commands work on directories now, just as they work on files. So do svn
copy and svn move. However, these commands do not cause any kind of immediate change in the
repository. Instead, the working items are simply “scheduled” for addition or deletion. No repository
changes happen until you run svn commit.
Directories aren't dumb containers anymore; they have revision numbers like files. (Or more properly, it's correct to talk about “directory foo/ in revision 5”.)
Let's talk more about that last point. Directory versioning is a hard problem; because we want to allow
mixed-revision working copies, there are some limitations on how far we can abuse this model.
From a theoretical point of view, we define “revision 5 of directory foo” to mean a specific collection
of directory-entries and properties. Now suppose we start adding and removing files from foo, and then
commit. It would be a lie to say that we still have revision 5 of foo. However, if we bumped foo's revision number after the commit, that would be a lie too; there may be other changes to foo we haven't yet
received, because we haven't updated yet.
Subversion deals with this problem by quietly tracking committed adds and deletes in the .svn area.
Subversion for CVS Users
When you eventually run svn update, all accounts are settled with the repository, and the directory's
new revision number is set correctly. Therefore, only after an update is it truly safe to say that you have
a “perfect” revision of a directory. Most of the time, your working copy will contain “imperfect” directory revisions.
Similarly, a problem arises if you attempt to commit property changes on a directory. Normally, the
commit would bump the working directory's local revision number. But again, that would be a lie, because there may be adds or deletes that the directory doesn't yet have, because no update has happened.
Therefore, you are not allowed to commit property-changes on a directory unless the directory is upto-date.
For more discussion about the limitations of directory versioning, see the section called “The Limitations of Mixed Revisions”.
More Disconnected Operations
In recent years, disk space has become outrageously cheap and abundant, but network bandwidth has
not. Therefore, the Subversion working copy has been optimized around the scarcer resource.
The .svn administrative directory serves the same purpose as the CVS directory, except that it also
stores read-only, “pristine” copies of your files. This allows you to do many things off-line:
svn status
Shows you any local changes you've made (see the section called “svn status”)
svn diff
Shows you the details of your changes (see the section called “svn diff”)
svn revert
Removes your local changes (see the section called “svn revert”)
Also, the cached pristine files allow the Subversion client to send differences when committing, which
CVS cannot do.
The last subcommand in the list is new; it will not only remove local mods, but it will un-schedule operations such as adds and deletes. It's the preferred way to revert a file; running rm file; svn update will
still work, but it blurs the purpose of updating. And, while we're on this subject…
Distinction Between Status and Update
In Subversion, we've tried to erase a lot of the confusion between the cvs status and cvs update commands.
The cvs status command has two purposes: first, to show the user any local modifications in the working copy, and second, to show the user which files are out-of-date. Unfortunately, because of CVS's
hard-to-read status output, many CVS users don't take advantage of this command at all. Instead, they've
developed a habit of running cvs up to quickly see their mods. Of course, this has the side effect of
merging repository changes that you may not be ready to deal with!
With Subversion, we've tried to remove this muddle by making the output of svn status easy to read for
both humans and parsers. Also, svn update only prints information about files that are updated, not local modifications.
Here's a quick guide to svn status. We encourage all new Subversion users to use it early and often:
svn status Prints All Files That Have Local Modifications: The Network is not
Accessed by Default
Subversion for CVS Users
Add out-of-dateness information from repository.
Show all entries under version control.
The status command has two output formats. In the default “short” format, local modifications look like
% svn status
If you specify the --show-updates (-u) switch, a longer output format is used:
% svn status -u
Head revision:
In this case, two new columns appear. The second column contains an asterisk if the file or directory is
out-of-date. The third column shows the working-copy's revision number of the item. In the example
above, the asterisk indicates that faces.html would be patched if we updated, and that bloo.png is
a newly added file in the repository. (The - next to bloo.png means that it doesn't yet exist in the working copy.)
Lastly, here's a quick summary of the most common status codes that you may see:
Resource is scheduled for Addition
Resource is scheduled for Deletion
Resource has local modifications
Resource has conflicts (changes have not been completely merged
between the repository and working copy version)
Resource is external to this working copy (comes from another
repository. See the section called “svn:externals”)
Resource is not under version control
Resource is missing or incomplete (removed by another tool than
Subversion has combined the CVS P and U codes into just U. When a merge or conflict occurs, Subversion simply prints G or C, rather than a whole sentence about it.
For a more detailed discussion of svn status, see the section called “svn status”.
Branches and Tags
Subversion doesn't distinguish between filesystem space and “branch” space; branches and tags are ordinary directories within the filesystem. This is probably the single biggest mental hurdle a CVS user will
Subversion for CVS Users
need to climb. Read all about it in Chapter 4, Branching and Merging
Since Subversion treats branches and tags as ordinary directories, always remember to check
out the trunk ( of your project,
and not the project itself ( If you make the
mistake of checking out the project itself, you'll wind up with a working copy that contains a
copy of your project for every branch and tag you have.44
Meta-data Properties
A new feature of Subversion is that you can attach arbitrary metadata to files and directories. We refer to
this data as properties, and they can be thought of as collections of arbitrary name/value pairs attached
to each item in your working copy.
To set or get a property name, use the svn propset and svn propget subcommands. To list all properties
on an object, use svn proplist.
For more information, see the section called “Properties”.
Conflict Resolution
CVS marks conflicts with in-line “conflict markers”, and prints a C during an update. Historically, this
has caused problems, because CVS isn't doing enough. Many users forget about (or don't see) the C after
it whizzes by on their terminal. They often forget that the conflict-markers are even present, and then accidentally commit files containing conflict-markers.
Subversion solves this problem by making conflicts more tangible. It remembers that a file is in a state
of conflict, and won't allow you to commit your changes until you run svn resolved. See the section
called “Resolve Conflicts (Merging Others' Changes)” for more details.
Binary Files and Translation
In the most general sense, Subversion handles binary files more gracefully than CVS does. Because
CVS uses RCS, it can only store successive full copies of a changing binary file. But internally, Subversion expresses differences between files using a binary-differencing algorithm, regardless of whether
they contain textual or binary data. That means that all files are stored differentially (compressed) in the
repository, and small differences are always sent over the network.
CVS users have to mark binary files with -kb flags, to prevent data from being garbled (due to keyword
expansion and line-ending translations). They sometimes forget to do this.
Subversion takes the more paranoid route: first, it never performs any kind of keyword or line-ending
translation unless you explicitly ask it do so (see the section called “svn:keywords” and the section
called “svn:eol-style” for more details). By default, Subversion treats all file data as literal byte strings,
and files are always stored in the repository in an untranslated state.
Second, Subversion maintains an internal notion of whether a file is “text” or “binary” data, but this notion is only extant in the working copy. During an svn update, Subversion will perform contextual
merges on locally modified text files, but will not attempt to do so for binary files.
To determine whether a contextual merge is possible, Subversion examines the svn:mime-type
property. If the file has no svn:mime-type property, or has a mime-type that is textual (e.g. text/*),
That is, providing you don't run out of disk space before your checkout finishes.
Subversion for CVS Users
Subversion assumes it is text. Otherwise, Subversion assumes the file is binary. Subversion also helps
users by running a binary-detection algorithm in the svn import and svn add commands. These commands will make a good guess and then (possibly) set a binary svn:mime-type property on the file
being added. (If Subversion guesses wrong, the user can always remove or hand-edit the property.)
Versioned Modules
Unlike CVS, a Subversion working copy is aware that it has checked out a module. That means that if
somebody changes the definition of a module, then a call to svn update will update the working copy
Subversion defines modules as a list of directories within a directory property: see the section called
“Externals Definitions”.
With CVS's pserver, you are required to “login” to the server before any read or write operation—you
even have to login for anonymous operations. With a Subversion repository using Apache HTTPD as
the server, you don't provide any authentication credentials at the outset—if an operation that you perform requires authentication, the server will challenge you for your credentials (whether those credentials are username and password, a client certificate, or even both). So if your repository is worldreadable, you will not be required to authenticate at all for read operations.
As with CVS, Subversion still caches your credentials on disk (in your ~/.subversion/auth/ directory) unless you tell it not to by using the --no-auth-cache switch.
Converting a Repository from CVS to Subversion
See the section called “Repository Converters”.
Appendix B. Troubleshooting
Common Problems
There are a number of problems you may run into in the course of installing and using Subversion.
Some of these will be resolved once you get a better idea of how Subversion does things, while others
are caused because you're used to the way that other version control systems work. Still other problems
might be unsolvable due to bugs in some of the operating systems that Subversion runs on (considering
the wide array of OS'es that Subversion runs on, it's amazing that we don't encounter many more of
The following list has been compiled over the course of several years of Subversion usage, and they
cover just about every frequently occurring problem that you'll see in Subversion—from building, to installing, to using Subversion. If you can't find the problem you're having here, or you've tried everything
we recommend with no success, send mail to <> with a detailed
description of the problem you're having 45
Problems Using Subversion
Every time I try to access my repository, svn just hangs.
Every time I try to run svn, it says my working copy is locked.
I'm getting errors finding or opening a repository, but I know my repository URL is correct.
How can I specify a Windows drive letter in a file:// URL?
I'm having trouble doing write operations to a Subversion repository over a network.
Under Windows XP, the Subversion server sometimes seems to send out corrupted data.
What is the best method of doing a network trace of the conversation between a Subversion client
and server?
Problems Building Subversion
I just built the distribution binary, and when I try to check out Subversion, I get an error about an
“Unrecognized URL scheme”.
When I run configure, I get errors like subs-1.sed line 38: Unterminated `s' command.
I'm having trouble building Subversion under Windows with MSVC++ 6.0.
Problems Using Subversion
Every Time I Try to Access My Repository, My Subversion Client
Remember that the amount of detail you provide about your setup and your problem is directly proportional to the likelihood of
getting an answer from the mailing list. You're encouraged to include everything short of what you had for breakfast and your
mother's maiden name.
Just Hangs.
Subversion uses Berkeley DB, which keeps your data in a series of database files. Berkeley DB is journaling system, meaning that it logs every action it is about to perform before it actually performs the action. If your client is interrupted while in the process of talking to the database, then a lockfile is left behind in the database, along with a log file describing the unfinished actions.
Any other client that attempts to access the database will just hang, waiting for the lockfile to disappear.
To awaken your repository, you need to tell Berkeley DB to either finish the work, or rewind the
database to a previous state that is known to be consistent. To do this, run the following command from
the machine that contains your Subversion Repository:
$ svnadmin recover /path/to/repos
Be sure that you disable all access to the repository before doing this (by shutting down httpd or
svnserve). Make sure you run this command as the user that owns and manages the database, and not as
root, else it will leave root-owned files in the db/ directory which cannot be opened by the non-root
user that manages the database, which is typically either you or your Apache httpd process.
Every Time I Try to Run svn, It Says My Working Copy is Locked.
Subversion's working copy, just like Berkeley DB, uses a journaling mechanism to perform all actions.
That is, it logs everything it is about to do before it does so. If svn is interrupted while performing an action, then one or more lockfiles are left behind, along with log files describing then unfinished actions.
(svn status will show an L next to locked directories.)
Any other process that attempts to access the working copy will fail when it sees the locks. To awaken
your working copy, you need to tell the svn client to finish the work. To fix this, run this command from
the top of your working copy:
$ svn cleanup working-copy
I'm Getting Errors Finding or Opening a Repository, but I Know My
Repository URL is Correct.
See the section called “Every Time I Try to Access My Repository, My Subversion Client Just Hangs.”.
How can I specify a Windows drive letter in a file:// URL?
See Repository URLs.
I'm Having Trouble Doing Write Operations to a Subversion Repository over a Network
If import works fine over local access:
$ mkdir test
$ touch test/testfile
$ svn import test file:///var/svn/test -m "Initial import"
Transmitting file data .
Committed revision 1.
But not from a remote host:
$ svn import test -m "Initial import"
harry's password: xxxxxxx
svn_error: #21110 :
The specified activity does not exist.
We've seen this when the REPOS/dav/ directory is not writable by the httpd process. Check the permissions to ensure that Apache httpd can write to the dav/ directory (and to the corresponding db/ directory, of course).
Under Windows XP, the Subversion Server Sometimes Seems to
Send Out Corrupted Data.
You need to install Window XP Service Pack 1. You can get all sorts of information about that Service
Pack at;EN-US;q317949
for details.
What is the Best Method of Doing a Network Trace of the Conversation Between a Subversion Client and Server?
Use Ethereal to eavesdrop on the conversation:
The following instructions are specific to the graphical version of Ethereal, and may not apply
to the command line version (whose binary is usually named tethereal).
Pull down the Capture menu, and choose Start.
Type port 80 for Filter, and turn off promiscuous mode.
Run your Subversion client.
Hit Stop. Now you have a capture. It looks like a huge list of lines.
Click on the Protocol column to sort.
Then, click on the first relevant TCP line to select it.
Right click, and choose Follow TCP Stream. You'll be presented with the request/response pairs of
the Subversion client's HTTP conversion.
Alternatively, you may set the http-debug parameter in the server's configuration file to cause neon's debugging output to appear when you run the svn client. The numeric value of neon-debug is a combination of the NE_DBG_* values in the header file ne_utils.h. Setting http-debug to 130 (i.e.
NE_DBG_HTTP + NE_DBG_HTTPBODY) will cause the HTTP data to be shown.
You may well want to disable compression when doing a network trace, see the compression parameter
in the config configuration file.
Problems Building Subversion
I Just Built the Distribution Binary, and When I Try to Check Out
Subversion, I Get an Error About an “Unrecognized URL Scheme”
Subversion uses a plugin system to allow access to repositories. Currently there are three of these plugins: ra_local allows access to a local repository, ra_dav which allows access to a repository via
WebDAV, and ra_svn allows local or remote access via the svnserve server. When you attempt to perform an operation in Subversion, the client tries to dynamically load a plugin based on the URL scheme.
A file:// URL will try to load ra_local, an http:// URL will try to load ra_dav, and so on.
The error you are seeing means that the dynamic linker/loader can't find the plugins to load. This normally happens when you build Subversion with shared libraries, then attempt to run it without first running make install' Another possible cause is that you ran make install, but the libraries were installed in a location that the dynamic linker/loader doesn't recognize. Under Linux, you can allow the
linker/loader to find the libraries by adding the library directory to /etc/ and running
ldconfig. If you don't wish to do this, or you don't have root access, you can also specify the library directory in the LD_LIBRARY_PATH environment variable.
When I Run configure, I Get Errors Like subs-1.sed line 38:
Unterminated `s' command
usr/local/bin/apu-config on your system. Remove them, make sure the apr/ and aprutil/ that you're building with are completely up-to-date, and try again.
I'm Having Trouble Building Subversion Under Windows with
MSVC++ 6.0.
You need to get the latest platform SDK. The one that ships with VCa++ 6.0 is not recent enough.
WebDAV is an extension to HTTP, and is growing more and more popular as a standard for filesharing. Today's operating systems are becoming extremely Web-aware, and many have now built-in
support for mounting “shares” exported by WebDAV servers.
If you use Apache/mod_dav_svn as your Subversion network server, then to some extent, you are also
running a WebDAV server. This appendix gives some background on the nature of this protocol, how
Subversion uses it, and how well Subversion interoperates with other software that is WebDAV-aware.
Basic WebDAV Concepts
This section provides a very brief, very general overview to the ideas behind WebDAV. It should lay the
foundation for understanding WebDAV compatibility issues between clients and servers.
Just Plain WebDAV
RFC 2518 defines a set of concepts and accompanying extension methods to HTTP 1.1 that make the
web into a more universal read/write medium. The basic idea is that a WebDAV-compliant web server
can act like a generic file server; clients can mount WebDAV “shares” that behave much like NFS or
SMB shares.
However, it's important to note that RFC 2518 does not provide any sort of model for version control,
despite the “V” in DAV. Basic WebDAV clients and servers assume only one version of each file or directory exists, and can be repeatedly overwritten. 46
Here are the new concepts and methods introduced in basic WebDAV:
New write methods
Beyond the standard HTTP PUT method (which creates or overwrites a web
resource), WebDAV defines new COPY and MOVE methods for duplicating
or rearranging resources.
This is simply the WebDAV term for a grouping of resources (URIs). In
most cases, it is analogous to a “directory”. You can tell something is a collection if it ends with a trailing “/”. Whereas file resources can be written or
created with a PUT method, collection resources are created with the new
MKCOL method.
This is same idea present in Subversion—metadata attached to files and collections. A client can list or retrieve properties attached to a resource with
the new PROPFIND method, and can change them with the PROPPATCH
method. Some properties are wholly created and controlled by users (e.g. a
property called “color”), and others are wholly created and controlled by the
WebDAV server (e.g. a property that contains the last modification time of a
file). The former kind are called “dead” properties, and the latter kind are
called “live” properties.
A WebDAV server may decide to offer a locking feature to clients—this
part of the specification is optional, although most WebDAV servers do offer the feature. If present, then clients can use the new LOCK and UNLOCK
methods to mediate access to a resource. In most cases these methods are
For this reason, some people jokingly refer to generic WebDAV clients as “WebDA” clients!
WebDAV and Autoversioning
used to create exclusive write locks (as discussed in the section called “The
Lock-Modify-Unlock Solution”), although shared write locks are also possible.
DeltaV Extensions
Because RFC 2518 left out versioning concepts, another capable group was left with the responsibility
of writing RFC 3253, which adds versioning to WebDAV. WebDAV/DeltaV clients and servers are often called just “DeltaV” clients and servers, since DeltaV implies the existence of basic WebDAV.
DeltaV introduces a whole slew of new acronyms, but don't be intimidated. The ideas are fairly straightforward. Here are the new concepts and methods introduced in DeltaV:
Per-resource versioning
Like CVS and other version-control systems, DeltaV assumes that
each resource has a potentially infinite number of states. A client
begins by placing a resource under version control using the new
VERSION-CONTROL method. This creates a new Version Controlled Resource (VCR). Every time you change the VCR (via
PUT, PROPPATCH, etc.), a new state of the resource is created,
called a Version Resource (VR). VCRs and VRs are still ordinary
web resources, defined by URLs. Specific VRs can have humanfriendly names as well.
Server-side working-copy model
Some DeltaV servers support the ability to create a virtual
“workspace” on the server, where all of your work is performed.
Clients use the MKWORKSPACE method to create a private area,
then indicate they want to change specific VCRs by “checking
them out” into the workspace, editing them, and “checking them
in” again. In HTTP terms, the sequence of methods would be
created, and edited VCR's contents now “point to” the latest VR.
Each VCR has also has a “history” resource which tracks and orders its various VR states.
Client-side working-copy model
Some DeltaV servers also support the idea that the client may
have a private working copy full of specific VRs. (This is how
CVS and Subversion work.) When the client wants to commit
changes to the server, it begins by creating a temporary server
transaction (called an activity) with the MKACTIVITY method.
The client then performs a CHECKOUT on each VR it wishes to
change, which creates a number of temporary “working
resources” in the activity, that can be modified using PUT and
PROPPATCH methods. Finally, the client performs a CHECKIN
on each working resource, which creates a new VR within each
VCR, and the entire activity is deleted.
DeltaV allows you define flexible collections of VCRs called
“configurations”, which don't necessarily respond to particular directories. Each VCR's contents can be made to point to a specific
VR using the UPDATE method. Once the configuration is perfect,
the client can create a “snapshot” of the whole configuration,
called a “baseline”. Clients use the CHECKOUT and CHECKIN
methods to capture specific states of configurations, much like
they use these methods to create specific VR states of VCRs.
DeltaV defines a new method, REPORT, which allows the client
WebDAV and Autoversioning
and server to perform customized data exchanges. The client
sends a REPORT request with a properly-labeled XML body full
of custom data; assuming the server understands the specific report-type, it responds with an equally custom XML body. This
technique is very similar to XML-RPC.
For many, this is the “killer” feature of DeltaV. If the DeltaV
server supports this feature, then basic WebDAV clients (i.e.
those unaware of versioning) can still write to the server, and the
server will silently perform versioning anyway. In the simplest
example, an ignorant PUT from a basic WebDAV client might be
translated by the server as a CHECKOUT, PUT, CHECKIN.
Subversion and DeltaV
So how “compatible” is Subversion with other DeltaV software? In two words: not very. At least not
yet, not in Subversion 1.0.
While libsvn_ra_dav sends DeltaV requests to the server, the Subversion client is not a general-purpose
DeltaV client. In fact, it expects some custom features from the server (especially through custom REPORT requests). Further, mod_dav_svn is not a general-purpose DeltaV server. It only implements a
strict subset of the DeltaV specification. A more general WebDAV or DeltaV client may very well be
able to interoperate against it, but only if that client operates within the narrow confines of those features
that the server has implemented. The Subversion development team plans to address general WebDAV
interoperability in a future release of Subversion.
Mapping Subversion to DeltaV
Here is a very “high-level” description of how various Subversion client operations use DeltaV. In many
cases, these explanations are gross oversimplifications. They should not be taken as a substitute for reading Subversion's source code or talking with its developers.
svn checkout/list
Perform a PROPFIND of depth 1 on the collection to get a list of
immediate children. Perform a GET (and possibly a PROPFIND)
on each child. Recurse into collections and repeat.
svn commit
Create an activity with MKACTIVITY, and do a CHECKOUT of
each changed item, followed by a PUT of new data. Finally, a
MERGE request causes an implicit CHECKIN of all working resources.
svn update/switch/status/merge/diff
Send a custom REPORT request that describes the mixed-revision
(and mixed-url) state of the working copy. The server sends a custom response that describes which items need updating. The client
loops over the response, performing GET and PROPFIND requests as needed. For updates and switches, install the new data in
the working copy. For diff and merge commands, compare the
data to the working copy, possibly applying changes as local
Autoversioning Support
At the time of writing, the truth is that there are very few DeltaV clients in the world; RFC 3253 is still
WebDAV and Autoversioning
relatively new. However users do have access to “generic” clients, because almost every modern operating system now has an integrated basic WebDAV client. With this in mind, Subversion developers realized that if Subversion 1.0 was to have any interoperability features, support for DeltaV autoversioning
would be the best approach.
To activate autoversioning in mod_dav_svn, use the SVNAutoversioning directive within the
httpd.conf Location block, like so:
<Location /repos>
DAV svn
SVNPath /absolute/path/to/repository
SVNAutoversioning on
Normally, if a generic WebDAV client attempted a PUT to a path within your repository location,
mod_dav_svn would outright reject the request. (It normally only allows such operations on “working
resources” within DeltaV “activities”.) With SVNAutoversioning turned on, however, the server interprets the PUT request as an internal MKACTIVITY, CHECKOUT, PUT, and CHECKIN. A generic log
message is auto-generated, and a new filesystem revision is created.
Because so many operating systems already have integrated WebDAV abilities, the use-case for this feature borders on fantastical: imagine an office of ordinary users running Microsoft Windows or Mac OS.
Each computer “mounts” the Subversion repository, which appears to be an ordinary network share.
They use the server as they always do: open files from the server, edit them, and save them back to the
server. But in this fantasy, the server is automatically versioning everything. Later on, a sysadmin can
use a Subversion client to search and retrieve all older versions.
Is this fantasy real? Not quite. The main snag is that Subversion 1.0 has no support whatsoever for the
WebDAV LOCK or UNLOCK methods. Most operating system DAV clients attempt to LOCK a resource
opened directly from a DAV-mounted network share. For now, users may have to copy a file from the
DAV share to local disk, edit the file, then copy it back again. Not ideal autoversioning, but still doable.
The mod_dav_lock Alternative
The mod_dav Apache module is a complex beast: it understands and parses all of the WebDAV and
DeltaV methods, yet it depends on a back-end “provider” to access the resources themselves.
In its simplest incarnation, a user can use mod_dav_fs as a provider for mod_dav. mod_dav_fs uses the
ordinary filesystem to store files and directories, and only understands vanilla WebDAV methods, not
Subversion, on the other hand, uses mod_dav_svn as a provider for mod_dav. mod_dav_svn understands
all WebDAV methods except LOCK, and understands a sizable subset of DeltaV methods. It accesses
data in the Subversion repository, rather than in the real filesystem. Subversion 1.0 doesn't support locking, because it would actually quite difficult to implement, since Subversion uses the copy-modify-merge model.47
In Apache httpd-2.0, mod_dav supports the LOCK method by tracking locks in a private database, assuming that the provider is willing to accept them. In Apache httpd-2.1 or later, however, this locking
support has been broken into an independent module, mod_dav_lock. It allows any mod_dav provider to
take advantage of the lock database, including mod_dav_svn, even though mod_dav_svn doesn't actually understand locking.
Confused yet?
In a nutshell, you can use mod_dav_lock in Apache httpd-2.1 (or later) to create the illusion that
Subversion may someday develop a reserved-checkout locking model that can live peaceably with copy-modify-merge, but it
probably won't happen soon.
WebDAV and Autoversioning
mod_dav_svn is honoring LOCK requests. Make sure mod_dav_lock is either compiled into httpd, or being loaded in your httpd.conf. Then simply add the DAVGenericLockDB directive to your Location like so:
<Location /repos>
DAV svn
SVNPath /absolute/path/to/repository
SVNAutoversioning on
DavGenericLockDB /path/to/store/locks
This technique is a risky business; in some sense, the mod_dav_svn is now lying to the WebDAV client.
It claims to accept the LOCK request, but in reality the lock isn't being enforced at all levels. If a second
WebDAV client attempts to LOCK the same resource, then mod_dav_lock will notice and correctly deny
the request. But there's absolutely nothing preventing an ordinary Subversion client from changing the
file via a normal svn commit! If you use this technique, you're giving users the opportunity to stomp on
each others' changes. In particular, a WebDAV client might accidentally overwrite a change committed
by regular svn client.
On the other hand, if you set up your environment very carefully, you may mitigate the risk. For example, if all of your users are working though basic WebDAV clients (rather than svn clients), then things
should be fine.
Autoversioning Interoperability
In this section, we'll describe the most common generic WebDAV clients (at the time of writing), and
how well they operate against a mod_dav_svn server using the SVNAutoversioning directive. RFC
2518 is a bit large, and perhaps a bit too flexible. Every WebDAV client behaves slightly differently,
and creates slightly different problems.
Win32 WebFolders
Windows 98, 2000, and XP have an integrated WebDAV client known as “WebFolders”. On Windows
98, the feature might need to be explicitly installed; if present, a “WebFolders” directory appears directly within My Computer. On Windows 2000 and XP, simply open My Network Places, and run the
Add Network Place icon. When prompted, enter the WebDAV URL. The shared folder will appear
within My Network Places.
Most write operations work fine against an autoversioning mod_dav_svn server, but there are few problems:
If the computer is a member of an NT Domain, then it seems to be unable to connect to the WebDAV share. It repeatedly asks for a name and password, even when the Apache server isn't issuing
an authentication challenge! Some have speculated that this might happen because WebFolders is
specifically designed to operate against Microsoft's SharePoint DAV server. If the machine isn't part
of an NT Domain, then the share is mounted without a problem. This mystery is not yet solved.
A file can't be opened for direct editing from the share; it always comes up read-only. The
mod_dav_lock technique doesn't help, because WebFolders doesn't use the LOCK method at all. The
previously mentioned “copy, edit, re-copy” method does work, however. The file on the share can be
successfully overwritten by a locally edited copy.
Mac OS X
WebDAV and Autoversioning
Apple's OS X operating system has an integrated WebDAV client. From the Finder, select the “Connect
to Server” item from the Go menu. Enter a WebDAV URL, and it appears as a disk on the desktop, just
like any file server.48
Unfortunately, this client refuses to work against an autoversioning mod_dav_svn because of its lack of
LOCK support. Mac OS X discovers the missing LOCK ability during the initial HTTP OPTIONS feature
exchange, and thus decides to mount the Subversion repository as a read-only share. After that, no write
operations are possible at all. In order to mount the repository as a read-write share, you must use the
mod_dav_lock trick discussed previously. Once locking seems to work, the share behaves very nicely:
files can be opened directly in read/write mode, although each save operation will cause the client to do
a PUT to a temporary location, a DELETE of original file, and a MOVE of the temporary resource to the
original filename. That's three new Subversion revisions per save!
One more word of warning: OS X's WebDAV client can be overly sensitive to HTTP redirects. If you're
unable to mount the repository at all, you may need to enable the BrowserMatch directive in your
BrowserMatch "^WebDAVFS/1.[012]" redirect-carefully
Unix: Nautilus 2
Nautilus is the official file manager/browser for the GNOME desktop. Its main home page is at By simply typing a WebDAV URL into the
Nautilus window, the DAV share appears like a local filesystem.
In general, Nautilus 2 works reasonably well against an autoversioning mod_dav_svn, with the following caveats:
Any files opened directly from the share are treated as read-only. Even the mod_dav_lock trick
seems to have no effect. It seems that Nautilus never issues the LOCK method at all. The “copy locally, edit, copy back” trick does work, however. Unfortunately, Nautilus overwrites the old file by
issuing a DELETE first, which creates an extra revision.
When overwriting or creating a file , Nautilus first does a PUT of an empty file, then overwrites it
with a second PUT. This creates two Subversion filesystem revisions, rather than one.
When deleting a collection, it issues an HTTP DELETE on each individual child instead of on the
collection itself. This creates a whole bunch of new revisions.
Linux davfs2
Linux davfs2 is a filesystem module for the Linux kernel, whose development is located at Once installed, a WebDAV network share can be mounted
with the usual Linux mount command.
The word on the street is that this DAV client doesn't work at all with mod_dav_svn's autoversioning.
Every single attempt to write to the server is preceded by a LOCK request, which mod_dav_svn doesn't
support. At this time, there is no data indicating whether the use of mod_dav_lock resolves this problem.
Unix users can also run mount -t webdav URL /mountpoint.
Appendix D. Other Subversion Clients
Out of One, Many
The Subversion command line client, svn, is the official49 implementation of a Subversion client. Fortunately for those interested in developing additional Subversion clients, Subversion is implemented as a
series of libraries. These libraries are accessible via C API, as well as other languages (see the section
called “Using Languages Other than C and C++”).
This component design means that it's easy (well, at least easier) to write clients and utilities using these
libraries. As a result, even pre-1.0, there are a number of GUI clients available for Subversion, each in
various phases of development.
We used to describe all those clients here, but lately there are too many of them, and they're moving too
fast, for a printed manual to keep track of them. So instead, we recommend you to the links page at, which is kept reasonably up to
Because we says so, that's why.
Appendix E. Third Party Tools
Subversion's modular design (covered in the section called “Layered Library Design”) and the availability of language bindings (as described in the section called “Using Languages Other than C and C++”)
make Subversion a likely candidate for use as an extension or backend to other pieces of software. In
this appendix, we'll introduce you to some of the third-party tools that work with Subversion. We will
not cover actual Subversion clients—see Appendix E, Third Party Tools for those.
Repository Converters
There are several different converters available to turn your CVS repository into a Subversion repository. We'll mention a few here, but you should also check the list at to see if any new ones
have been added.
cvs2svn is a Python script that converts a CVS repository to a
Subversion repository. It is under active development. It currently
ships with Subversion, though it may become an independent
project soon. For now, you should always run the most recent version you can, by checking out this subdirectory of the Subversion
cvs2svn/. For more information about, read the
README file in that subdirectory. As of this writing (February
2004), is not really "1.0 quality": it has successfully
converted many people's repositories (including branches and
tags), but for others it has either failed to complete the conversion,
or converted the data in an unexpected or subtly wrong way.
However, by the time you read this, the situation may have
changed; check the README for updates.
Subversion plugin for VCP
Chia-liang Kao has written a converter based on VCP. The converter doesn't seem to have its own name, it's just "the Subversion
plugin to VCP", but it can be checked out from
/lib/VCP/Dest/ It depends on the Subversion Perl
bindings as well as VCP. (For more information about VCP, see
Lev Serebryakov has written a converter called RefineCVS,
from We
don't have any direct experience with it.
Perhaps the first—and definitely the most popular—utility to take advantage of Subversion's public API
is ViewCVS. ViewCVS is essentially a CGI script which enables browsing of the files and directories of
a version control system. Originally designed as a Python-based replacement for the popular cvsweb
Third Party Tools
utility, 50 ViewCVS provides a full-featured Web-based interface to CVS repositories, allowing folks to
see the version control history of the files in those repositories and to perform such nifty tasks as generating differences between arbitrary versions of those files.
In the early part of 2002, the repository accessing portion of ViewCVS was modularized into a semigeneric interface, and a pair of modules were grown to provide that functionality for CVS repositories.
Later that year, Subversion's Python language bindings sufficiently matured, and a Subversion repository module was written for the ViewCVS interface. Now, ViewCVS is able to browse Subversion
repositories, providing essentially the same history and differencing mechanisms for those repositories
as are available for CVS ones.
For more information on ViewCVS, see the project's website at
SubWiki is a Subversion-backed Wiki program. Wikis have sprung up on the World Wide Web as
unique publishing and community tools—essentially, web-based interfaces for editing web pages. SubWiki takes the Wiki concept one step further by using a version control system for its backend storage
mechanism. The result is a CGI program which allows web pages to be essentially edited in-place, yet
never loses old versions of those web pages.
To learn more about SubWiki, visit that project's website at
CVSWeb was written in Perl.
An svn command that is used to add a file or directory to a repository.