Linux Journal - November 2011

Linux Journal - November 2011
OLPC | Arduino | Trim-Slice | vDSO | Elmer | MPD
™
One LaptOp per
ChiLd StatuS repOrt
uSe YOur phOne tO
LOCk YOur SCreen
autOmatiCaLLY
Since 1994: The Original Magazine of the Linux Community
NOveMber 2011 | ISSUe 211 |
www.linuxjournal.com
hack thiS
Build an
ultra-lowPower Server
with the trim-Slice
Set Up a Music
System That
Follows You Around
LJ211-November2011.indd 1
Get Started
Programming
the Arduino
+
How To:
Add A
Custom
vdso to
A Linux
KerneL
Create a Unified
Boot Environment
on a USB Drive
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CONTENTS
NOVEMBER 2011
ISSUE 211
HACK THIS
FEATURES
58
Building an Ultra-LowPower File Server with
the Trim-Slice
Try this for power, space and
noise savings.
Daniel Bartholomew
68
Learning to Program
the Arduino
Blink some LEDs, create some noise,
do something useful and fun.
Amit Saha
82
Roaming Media
Let your music come to you, no matter where you are in your house.
Michael Nugent
58
TRIM-SLICE
68
ARDUINO
One Key to Rule Them All:
GRUB, USB and a Multboot
Environment
88
Set up GRUB on a USB drive and
configure it with multiple boot
options, all installed on the
same drive.
Adrian Hannah
4 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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COLUMNS
30
Reuven M. Lerner’s At the Forge
36
Dave Taylor’s Work the Shell
40
Kyle Rankin’s Hack and /
2011 Book Roundup
Working with Image Files, Part II
Automatically Lock Your Computer
116 Doc Searls’ EOF
Losing Its Way
INDEPTH
98
OLPC: Are We There Yet?
106
Creating a vDSO: the Colonel’s
Other Chicken
Creating a vDSO is surprsingly
simple, but making it useful for
sharing data between the kernel and
user memory can be rather involved.
Matt Davis
OLPC currently has more than two
million laptops in the hands of
children in more than 25 languages
in more than 40 countries.
Sameer Verma
IN EVERY ISSUE
40
AUTOMATICALLY LOCK YOUR COMPUTER
8
Current_Issue.tar.gz
10
Letters
18
UPFRONT
46
New Products
50
New Projects
117
Advertisers Index
ON THE COVER
• One Laptop Per Child Status Report, p. 98
• Use Your Phone to Lock Your Screen Automatically, p. 40
• Build an Ultra-Low-Power Server with the Trim-Slice, p. 58
• How-To: Add a Custom vDSO to a Linux Kernel, p. 106
• Set Up a Music System That Follows You Around, p. 82
• Get Started Programming the Arduino, p. 68
• Create a Unified Boot Environment on a USB Drive, p. 88
98
OLPC: ARE WE THERE YET?
COVER IMAGE: © Can Stock Photo Inc. / zphoto
LINUX JOURNAL (ISSN 1075-3583) is published monthly by Belltown Media, Inc., 2121 Sage Road, Ste. 310, Houston, TX 77056 USA. Subscription rate is $29.50/year. Subscriptions start with the next issue.
WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 5
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Technical Editor
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Hack Editor
Virtual Editor
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[email protected]
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[email protected]
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Current_Issue.tar.gz
SHAWN POWERS
To Hack, or
Not To Hack
O
f course, here at Linux Journal,
we choose “hack” every time.
My wife doesn’t always agree
with my world-modding attitude,
however. She seems to think switches,
and not cron jobs, should be used for
turning lights on and off. She doesn’t
understand why a person would want to
mount a broken laptop on the wall as a
digital picture frame. And, of course, I’m
not allowed to use the ultimate adhesive,
duct tape, on anything our guests might
see. Because she’s also the reason I’m
dressed, fed, shaved and showered most
days, I’m really not complaining, it’s
probably for the best.
This issue is all about hacks. If you’re
smart and ambitious, you usually can
make an awesome thing even better by
hacking it a bit. Reuven M. Lerner starts
off with a book review for 2011. Reading
is one of the best ways to get better at
hacking, whether it’s hardware hacking or
programming. Reuven reviews his favorite
programming books and lets us know what
he thinks. Dave Taylor follows him up with
part II of his series on working with images
within scripts. Hacking the command line
is cool, but hacking graphics with the
command line? Even cooler.
As one of my favorite television
characters, Sheldon Cooper, says,
“Everything is better with Bluetooth.”
Kyle Rankin and Michael Nugent show
us some interesting Bluetooth hacks this
month. Kyle addresses the problem of
forgetting to lock your workstation when
you walk away from it. In a home office,
that’s no big deal, but in cubicle-land, it
can be an open invitation for pranks. Kyle
shows how to lock your workstations
automatically by setting up a dæmon to
monitor when you (or more specifically,
the Bluetooth-enabled phone in your
pocket) wander away. Michael Nugent
takes the opposite approach, and using
Bluetooth proximity, he explains how
to make your media PCs play music to
certain speakers based on your location.
It’s a little like having the party follow
8 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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CURRENT_ISSUE.TAR.GZ
If you’re smart and ambitious, you usually
can make an awesome thing even better
by hacking it a bit.
you wherever you go!
Daniel Bartholomew takes a hack at
his power bill this month and writes
about the Trim-Slice server. If you like
the power savings a NAS device offers,
but want the power of a full-blown Linux
server, Daniel’s article is right up your
alley. He manages to run his new server
with only 15% of the power his last one
took. As someone with a server rack in
my home office, I’m seriously considering
scaling back the power.
No hacking issue would be complete
without some talk about Arduino.
Amit Saha teaches how to program the
little buggers and bend them to your
will. Arduino boards come with USB
nowadays, which makes interfacing
with them a snap. And, while we’re
talking about USB, it’s the perfect time
to mention Adrian Hannah’s article on
USB Flash drives. Adrian manages to hack
multiple Linux distributions into a single
USB drive, while providing persistent
storage as well. Along the way, you’ll
become a GRUB expert to boot. He’ll
make you Lord of the keyRings, even if
you’re not a hobbit!
A few years back, the One Laptop Per
Child Project took the world by storm
with its aggressively priced laptops
designed for kids in areas that are lacking
in technology. The OLPC Project has
taken its share of hits along the way,
but it’s still going strong. Sameer Verma
provides an update on the OLPC initiative
and describes the new hardware. Sugar
is still alive and well on the OLPC
computers, and, of course, so is Linux.
Don’t think we just hacked this issue
together though; we have the full
lineup of Linux and open-source-related
goodies you’ve come to love. Matt Davis
describes how to create a vDSO (Virtual
Dynamic Shared Object). John Knight
demonstrates PdfMasher, a tool for
converting PDFs into HTML, and James
Coyner shows how to tweak the Android
memory management system. Add to
that countless other geeky goodies, and
you have an issue that’s bound to please.
Oh, and if you want to use duct tape in
your hacks? Don’t worry, I won’t tell. ■
Shawn Powers is the Associate Editor for Linux Journal. He’s
also the Gadget Guy for LinuxJournal.com, and he has an
interesting collection of vintage Garfield coffee mugs. Don’t
let his silly hairdo fool you, he’s a pretty ordinary guy and
can be reached via e-mail at [email protected]
Or, swing by the #linuxjournal IRC channel on Freenode.net.
WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 9
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letters
I’ll Be in
My Hole
As a regular reader
(and now
subscriber)
to LJ, I think
Shawn Powers’
Current_issue.
tar.gz is always
a great setup
to the issue.
His column in the August 2011 issue is a
particular case in point. I read the opening
paragraph to my wife. Her reply to Shawn’s
“basement-dwellers” comment was “or
upstairs” (which happens to be the home
of my toys).
I would like to thank you and all the
contributors to your magazine. I came to
Linux as an antique of 57 (now 63)—a
retired “mainframe” developer unable to
afford the constant upgrades to Windows
development tools. Your magazine has
helped me immeasurably get over the Linux
learning curve as well as the fear factor.
Though I don’t consider myself agile in the
environment, Windows is nowhere to be
seen on my desktop, and tools like the Qt
SDK have permitted me to continue to
explore C++ and learn about genetic
algorithms and programming.
One question: with so many more-experienced and knowledgeable Linux/open-source
developers, how does someone with my
limited experience contribute back to the
community? I doubt there is much I can
offer. Thank you again for Linux Journal.
—Pete R.
Thanks for your kind words! As hard as it
might be to believe, I try to tone down my
silliness in Current_Issue.tar.gz so as not to
confuse non-native English speakers. In real
life, I’m much weirder. (I’m sure the rest of
the Linux Journal staff would agree!)
When it comes to contributing, the
standard answer is “documentation”.
That said, I’ve never once been able to
contribute documentation to a project,
so perhaps the standard answer needs to
be reconsidered. I think just using Linux,
and enjoying it, and letting other people
see you enjoy it will really do a lot for the
community. And, if you’re near a town
with a Linux Users Group, try to attend
meetings. They might have a need only
you can fill!—Shawn
What Day Is It?
I know Dave Taylor must be really tired
of everybody telling him how to better
parse the output of cal to get the day
of the week (see Dave Taylor’s Work the
Shell column in the June–September 2011
issues of LJ), but I figured I’d go a slightly
different route. Many years ago, I was
searching for an algorithm that would allow
10 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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[
me to calculate the correct day of the
week for a given date, and I found a great
one. I no longer can remember where I
found it, or who wrote it originally, but I
have converted it into pretty much every
language I use, and this last time was into
a bash script:
LETTERS
]
echo "or"
echo "
dow.sh 01-01-1970"
exit
fi
# Replace slashes or dashes on the input
# with spaces:
INTEXT=$(echo $1 | sed -e 's/[\/-]/ /g')
# Use the 'set' command to transfer to $1, $2, $3
#!/bin/bash
set $INTEXT
declare -a DAYS=(0 3 2 5 0 3 5 1 4 6 2 4)
# Call get_dow function with date to check:
declare -a DAYS_IN_WEEK=('Sunday' 'Monday' 'Tuesday'
get_dow "$1" "$2" "$3"
➥'Wednesday' 'Thursday' 'Friday' 'Saturday')
# Print day of week date falls on:
echo "${DAYS_IN_WEEK[$DOW]}"
get_dow() {
# $1 is month, $2 is day, $3 is year
# Strip off leading zeros from month and day:
MONTH=${1#0}
DAY=${2#0}
YEAR=$3
if [ $MONTH -lt 3 ]; then
Sorry, I don’t have a ton of error-detection
code in here, but I didn’t want to overcomplicate it.
By the way, I am an avid reader of Dave’s
Work the Shell column, along with the rest
of Linux Journal!
—Howard Pepper
YEAR=$((YEAR-1))
fi
MONTH=$((MONTH-1))
DOW=$(echo "($YEAR + ($YEAR/4) - ($YEAR/100)
➥+ ($YEAR/400) + ${DAYS[$MONTH]} + $DAY) % 7" | bc)
}
if [ "$1" == "" ]; then
Dave Taylor replies: Thanks for this,
Howard. A few people had told me that
there is a formula for calculating the day of
the week for any given date in the Julian
calendar, but try as I might, I couldn’t find
one that seemed to be reliable with leap
years and such. Now we have one, and it’s
a terrific shell script too.
echo "dow.sh - Prints the day of the week,
➥for a given date"
echo "
Where the date is in the format of mm/dd/yyyy
➥or mm-dd-yyyy"
echo "usage:"
echo "
dow.sh 01/01/1970"
More on Calculating Day of the Week
This is regarding Dave Taylor’s column in
the August 2011 issue. Despite Dave’s
remark that his solution may be more
complicated than necessary and that he’ll
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[
LETTERS
]
stick to it, I’d like to say why not use the
%w option of the date command? The
following command does the job just fine:
date +%w -d <datespec>
—Mayuresh Warunjikar
Dave Taylor replies: Well sure, if you
have that version of the date command,
but not every distro of Linux has all those
advanced capabilities.
Thanks for the New All-Digital Format
I just want to take a moment to
congratulate and thank you on your
transition to the new electronic format.
The new format renders perfectly on
my Sony PRS-600, and it has made the
publication an absolute joy to read! I’ve
been an avid reader for the past ten years.
—Joel Coulson
Thanks! I really enjoy reading on my
PRS-300, the pocket-size version of your
e-reader. My favorite part is how well
the Sony device handles the table of
contents.—Ed.
More Thanks for Going Digital-Only
Thanks for making your magazine digital
only. I remember the demise of TUX
magazine, which I really liked, but not
many, including me, subscribed to it. And
yes, I have subscribed to LJ for a year. I like
the convenience of digital subscriptions
and being able to click on articles and
advertisers for more information.
I’ve already learned something new
from your magazine today about JEdit
(see Adrian Klaver’s “JEdit: a Text Editor
and More” in the September 2011 issue
of LJ) and discovered it in my OpenSUSE
repo. I wish you luck and success.
—Robert Smits
That’s great to hear, Robert. I too was a TUX
subscriber long before I was on staff here
at Linux Journal. I enjoyed it back then, and
now with digital reading devices, I like the
LJ electronic version even more!—Ed.
Why Portrait Mode?
Like countless others (I’m sure), I was
surprised by your recent “digital-only”
announcement. Time will tell if this was
a great or bad decision. I’m hoping it
works out! Over the years, LJ has been a
wonderful spokesperson and learning tool
for the Linux community.
However, I don’t understand why when
a magazine goes digital, it still clings to
the old print format. Yes, most magazines and books are printed in “portrait”
mode. But, the majority of computers
are stuck in “landscape”. Formatting
in portrait forces me to page up/down
constantly, especially when you continue
having multiple columns. Maybe it’ll
work when I get my 60" hi-res monitor?
Best of luck with the new venture!
—Bob van der Poel
The layout part is a complicated endeavor.
12 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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Yes, landscape would make sense if it were
viewed as a PDF on computer screens only. (If
you remember TUX magazine, that is exactly
how it was done.) But, Linux Journal now
can be read on e-readers, which are mainly
in portrait mode. Then, there are the devices
that happily switch from portrait to landscape,
so we need to take that into account as well.
We are trying to offer the same content
in as many forms as possible. The PDF looks
like a traditional magazine, the epub/mobi
versions have flowing text and graphics
specifically designed for e-readers, and our
on-line interactive version was made for
Web browsers. On top of that, we have
the Android app, etc., etc. Ideally, with all
those options, we can cover everyone’s
preferences for the most part.—Ed.
Why, Why All-Digital?
I’m kind of pissed off at you guys. An
all-digital publication? No more driving
home from the post office, glancing at
the cover of the LJ on the seat beside me,
anticipating a good read of Linux Journal
next to the fire when I get home or over
coffee and a croissant tomorrow morning?
No more digging an old issue out of the
stack to show somebody some awesome
article on Java or Linux on Mars? I really
hate reading anything of any length on
my laptop; it’s a major PITA. Now I have to
think about getting some kind of e-reader,
and I can’t think of one I like. I actually
write code to produce epub- and mobiformatted e-books, and I can tell you there
isn’t an e-reader on the market today that’s
LJ211-November2011.indd 13
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[
LETTERS
]
worth the box it comes in. The Nook comes
closest, except it uses Adobe’s e-reader
SDK, which is almost as bad as the software
in the Kindle. Man I am really pissed!
I know you guys are between a rock
and a hard place. I work for a publisher,
and I can see the writing on the wall, but
“all-digital”? Jeesh.
—Scott Derrick
Scott, I know the switch is frustrating. Like
you said, working for a publisher, I’m sure
you weren’t surprised, but that doesn’t
mean you have to be happy about it! I miss
the old version as well, but I’m hoping as
a tech magazine, we can push through
this awkward time in publishing history
and come out the other side stronger and
wiser. Our readers are mostly geeks, and I
think this transition is actually easier for us
than it would be for a knitting magazine.
If technology magazines can get over this
hump, perhaps the non-tech magazines will
be able to follow our blazed trail. Big plans,
yes, but heck, we’re the operating system
that wants to take over the world!—Ed.
It Could Have Been Worse
I am perhaps an unusual subscriber. I am
79 years old and am not an administrator
or a programmer. My wife and I have used
Linux since Red Hat 5.2 (1999) and haven’t
used Windows for most of that time. I
have about six years remaining on my
subscription. I enjoy sitting in my easy chair
in the evening and reading Linux Journal.
I guess that is to be no more.
Still, it could have been worse. The
magazine could have folded completely.
At least I will have the digital copy; I just
won’t be able to sit in the recliner.
By the way, Dave Taylor and his Work the
Shell column is my favorite.
—Bruce Bales
Bruce, hopefully e-reader prices will
continue to fall, and you’ll be able to read
Linux Journal from your recliner once again.
Amazon seems to be doing a decent job
with its $79 Kindle. If nothing else, you
could move the easy chair over to the
computer desk. I’m just teasing of course,
but thank you for sticking with us.—Ed.
Wow, Podcasts, Facebook and More?
I was extremely pleased to get the August
2011 issue of LJ. I recently released a
social network site around podcasts
(http://weHEARus.com), so I was excited
to see Charles Olsen’s article on podcasting
as a way to share Linux knowledge. The
Git article by Henry Van Styn was also
a good read, since I currently am using
SVN and have considered Git, but I was
surprised you didn’t really go into its
“distributedness” aspect and how that
works. Also, although I already have
implemented Facebook’s “like” button, the
rest of Mike Diehl’s “Facebook Application
Development” article was very informative.
A mobile Facebook app is something that
is planned for the future. Do you have any
plans to delve further into the Facebook API
and publish articles on this? There was so
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[
much appropriately timed good stuff in the
August 2011 issue. Thanks for yet another
awesome one!
—Malcolm Beaulieu
Malcolm, I kind of feel like we should
“high five” or something! I’m really glad
you enjoyed the issue. Hopefully, this one
is as useful for you too.—Ed.
Suggestions
The diff -u (kernel development) column
by Zack Brown is my favorite by far (my
second favorite is Doc Searls’ EOF). I
like getting “the inside scoop” on some
projects I don’t follow closely. Is there any
chance of having a full two-page spread
LJ211-November2011.indd 15
LETTERS
]
with kernel development as well as some
monthly rotating FOSS project development
news besides the kernel? Even just a quick
summary of “important” discussions on
their respective mailing lists would be nice.
—Matthew Brush
Matthew, that’s an interesting idea; we’ll
have to talk about it and see what we come
up with. Thanks!—Ed.
Digital Television FCC Rules
Regarding R. E. Mackey’s letter in the
August 2011 issue of Linux Journal about
digital TV and the FCC: although not really
on the subject of Linux, many people do
not realize that the FCC’s regulations are
10/20/11 10:14 PM
[
LETTERS
]
openly accessible to anyone, if you know
where to look and what to look for.
You could say this is the broadcast
equivalent of what “use the Source, Luke”
would be, or the four-letter equivalent.
The relevant rules are found in the Code of
Federal Regulations Title 47 (47 CFR). For
broadcast TV, the relevant part is 73 (47 CFR
73—broadcast as a whole is assigned parts
70–79). And, note that the CFR really is written in code. There are specific definitions of
specific terms, and, to use an INTERCALism,
COME-FROMs abound. But code it is. And,
well, there are bugs in the code.
I mentioned “open”; see
http://www.gpo.gov/fdsys to see how
open. Browse into the Code of Federal
Regulations, and drill down to, say,
47CFR73.616 to see how interference
protection, post-DTV transition is worked
out. (Anyone who can follow LKML
should have no trouble finding it.)
The GPO is the Government Printing
Office, and it is in charge of publication
of rules and regulations. To see the law as
passed by Congress, you want the United
States Code. For the FCC, the relevant part
is Title 47 USC. Well, that’s an oversimplification. To use a revision control system’s
terminology, the USC is the trunk, and the
Public Laws as passed by Congress are the
commit logs (and the Federal Register is
the equivalent to LKML), and all are freely
available in electronic form, at the GPO.
I also meant “open” in another way. The
Media Bureau, which is over broadcast stations, has quite a bit of open-source code out
there, and it was a pioneer in government
open source. Drill down into Bureaus from the
main FCC page and find out for yourself.
Do note that the FCC.GOV site is huge. It
is easy to get lost in there, much like github
(and there is an FCC github).
—L. Owen
What to Do without Paper?
I understand that you have stopped (paper)
publishing your magazine—yet another
American (good) Linux magazine that is falling
off circulation. It is too bad. Our society has
found a more effective manner to publish. The
reality is that you can have more up-to-date
and timely content—that’s true, but Shawn,
an important question here: uh, uhm, what
am I to read during any important “business”
daily meeting? Well, I guess I’ll have to take
my laptop in with me from now on!
—Bob Wooden
Bob, you bring up the very reason I never
borrow someone else’s smartphone. And, now
I know to never borrow your laptop.—Shawn
Rip-off?
Your simplistic conversion of print
subscriptions to electronic subscriptions is
a rip-off. I paid for a print subscription and
have two years remaining.
Let’s review: Paid. For. A. Print.
Subscription. Get It?
Why? I can get a boat-load of on-line
Linux news for free. I paid for being able to
read it off-line. I won’t be renewing.
—MJD
16 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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The switch was sudden and frustrating for everyone—we
totally understand that. Unfortunately, we didn’t have a
choice. We are trying to offer as many digital options as
we can (PDF, epub, mobi, interactive on-line, Android app
and iPhone and iPad apps), but the print format just wasn’t
possible any longer. I am truly sorry you feel slighted.
Hopefully, you’ll find our digital offerings worthwhile at
least during the remainder of your subscription.—Ed.
Dream Come True
Linux Journal as digital-edition-only? Oh no, I thought,
when I was thinking about reading a PDF file on my
Notebook or my Kindle during my train ride to/from work.
What a surprise after I’ve realized that epub and mobi
versions also are ready for download. Now I’m able to read
my favourite Linux magazine comfortably on my Kindle.
Thank you guys, a dream came true!
—Thomas Balzer
Thomas, I’m really excited about the epub/mobi versions as
well. The PDF worked on my KindleDX, but on my smaller
Kindle and my Sony PRS-300, it really wasn’t easy to read.
The epub/mobi version is very convenient for me, and I’m
happy to see they are for you as well. Our Art Director,
Garrick Antikajian, really gets the credit for the epub
layout—three cheers for Garrick!—Ed.
Correction
Regarding my boto article “Python in the Clouds” in the
October 2011 issue: Mitchell Garnaat, the author of boto,
works for Eucalyptus Systems, not Canonical. I apologize
for the error.
—Adrian Klaver
WRITE LJ A LETTER We love hearing from our readers. Please send us
your comments and feedback via http://www.linuxjournal.com/contact.
At Your Service
SUBSCRIPTIONS: Linux Journal is available
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ext. 2.
WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 17
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UPFRONT
NEWS + FUN
diff -u
WHAT’S NEW IN KERNEL DEVELOPMENT
As Linus Torvalds released Linux 3.0
at long last, there followed a cascade
of minor breakages related solely to
the change in version number. Some of
these had to do with the kernel sources
themselves; others had to do with user
scripts out in the wild. The git tree had to
be renamed to git://git.kernel.org/pub/
scm/linux/kernel/git/torvalds/linux.git,
because the previous tree had “2.6”
in the URL. Then the kernel.org page
pointed to the wrong git tree, so that had
to be sorted out.
The kernel build scripts also expected
a three-numbered version number, with
an optional fourth (for the stable series),
while the 3.0 kernel will have only two,
with an optional third. But, it turns out that
there’s no easy answer, because the kernel
is so used to recognizing itself as a threenumbered entity, that it couldn’t (for now)
be made to identify as 3.0 internally.
A related problem is that some thirdparty software, including some that
exists in binary form only, can’t tolerate
the version number change. As Andi
Kleen reported, this means that Linux
3.0 is not fully backward-compatible with
Linux 2.6, even though the only cause
of that incompatibility is the version
number. He posted a patch to cause the
kernel to masquerade as a 2.6 kernel,
with an additional string tacked onto the
version number, indicating the proper
3.0 version. It’s about as ugly a solution
as you could imagine, but Andi said
that there didn’t seem to be any better
workaround that would still allow the
binary-only software to run under the
new kernels.
The OpenRISC architecture will be
included in the Linux kernel. OpenRISC is
a really cool hardware project for creating
an open-source CPU design. The project
has gone through various vicissitudes,
including being virtually dead for a while.
But, now there are about 25 developers
on the project, and they’ve had a kernel
port in development since 2.6.35. Jonas
Bonn recently submitted that code to
Linus Torvalds for inclusion, and it was
accepted readily enough, after a small
moment of confusion over whether a
related patch by Rusty Russell would be
cleaner to accept before or after Jonas’.
Another architecture also is well on the
way to being accepted into the kernel.
The C64x from Texas Instruments
recently got a GCC port, which means
it’s now possible to compile a full system
for that chip. The GCC port is actually
in a relatively early stage, but it’s still
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[
promising enough that Mark Salter
felt the time was right to post his patch
introducing the C64x architecture into
the kernel. He also set up a developer
wiki at linux-c6x.org.
An interesting detail about the C64x
processors is that they don’t support
cache coherency. In other words,
UPFRONT
]
multiple CPU cores are not guaranteed
to see the same data when they check
a given location in a shared data store.
Without cache coherency, supporting
SMP (Symmetric Multiprocessing) systems
is much more difficult. For now, C64x
systems may have to remain singleprocessor only. —ZACK BROWN
LinuxJournal.com
Since this issue is devoted to the fun and exciting world of hacking, consider this a friendly
reminder to visit our security section at http://www.linuxjournal.com/tag/security.
While most hacking you’ll read about here in Linux Journal is of the fun and
harmless variety, hacking occasionally comes in forms that can become a nuisance
or security risk to our dear readers. So, take some time to check out our offerings
at LinuxJournal.com, because you never know what threats lurk and what awesome
tips you might find for avoiding them. And, if that doesn’t convince you, just please
think of the children.
Give these a try to get started:
n “A Primer to the OAuth Protocol” by Adrian Hannah: http://www.linuxjournal.com/
article/10965.
n “Live-Fire Security Testing with Armitage and Metasploit” by Raphael Mudge:
http://www.linuxjournal.com/article/10973.
n “Linux Distro: Tails—You Can Never Be Too Paranoid“ by Michael Reed:
http://www.linuxjournal.com/content/
linux-distro-tales-you-can-never-be-too-paranoid.
—KATHERINE DRUCKMAN
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[
UPFRONT
]
Stop Installing
Outdated Ubuntu!
Have you ever installed Linux, only to be
greeted immediately with the system update
notification applet? If you have a fast Internet
connection or, even better, a local Ubuntu
mirror (see http://www.linuxjournal.com/
video/mirror-partner-repo-canonical
for some tips on creating your own local
mirror), you can use the “Installation
Minimal CD” and get a fully up-to-date
system the first time it boots.
Another advantage to using the Installation
Minimal CD is that it allows you to install
any official Ubuntu variant with the same
CD. Whether you want Ubuntu, Xubuntu,
Kubuntu or even the more specialized
*buntus for video editing and such, the
Minimal CD can do it. Download a copy at
https://help.ubuntu.com/community/
Installation/MinimalCD. It’s less than 20MB!
—SHAWN POWERS
Flow, Flow, Flow Your Code
Our recent transition to a fully
digital magazine has been exciting,
stressful, tumultuous and, thanks
to our readers, collaborative. As
we were converting our traditional
publishing skills into the digital
arena, we tried hard to preserve
the things that make magazines
popular. We didn’t want the magazine to
become less; we wanted it to become more.
Unfortunately, with all our efforts to maintain
useful layouts and provide interactive reading
apps, we did miss an important consumption
model: the traditional e-reader.
We’re so thankful for all the
feedback we received, and
continue to receive, regarding our
digital transition. Thanks to that
feedback, we now offer an epub
edition of Linux Journal, complete
with flowing text and functional
navigation for the vast majority of E Ink
devices. Yes, many devices can read PDF files,
but they’re just not pleasant to read on a
small screen. We’re excited about this issue,
and we hope you are too!—SHAWN POWERS
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[
UPFRONT
]
They Said It
“An empty stomach is not a good
political adviser.“ —Albert Einstein
“A question that sometimes drives me
hazy: am I or are the others crazy?“
—Albert Einstein
“A man should look for what is, and
not for what he thinks should be.“
—Albert Einstein
“Any man who can drive safely
while kissing a pretty girl is simply
not giving the kiss the attention it
deserves.“ —Albert Einstein
“Common sense is the collection of
prejudices acquired by age eighteen.“
—Albert Einstein
“Education is what remains after one
has forgotten what one has learned in
school.“ —Albert Einstein
Non-Linux
FOSS
Whether you’re trying
to use Google Voice and
a free SIP service to get
a free telephone system
or trying to connect to
your company’s internal
phone system, if you’re
on a Mac, you need a
SIP client. A few free
options exist, but none
are as simple as Alexei
Kuznetsov’s Telephone.
Telephone even
integrates with OS X’s
Contacts program, so
you can make a SIP call
directly from there. It’s
free, open source, and
it’s even available in
the Apple App Store.
If you need to make
a VoIP call on your
Macintosh, be sure to
check out Telephone:
http://www.tlphn.com.
—SHAWN POWERS
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[
UPFRONT
]
Tweak Your Android Memory
Management System
In my travels, I’ve discovered that not only
does the Linux community have a robust
following, but so does the Android hacking
community. My journey began two years
ago with the release of the Original Droid.
I had come from a Windows Mobile world
and didn’t know that phone hacking even
existed. Now hacking around on my Droid
is almost an everyday task.
Most of you own Android phones now,
and many of you already are running
hacked versions of Android, and many of
you already heavily tweak your builds. This
article is not for you. It’s an introduction
to the world of Android customization,
intended for Android users who don’t yet
know how to tweak their devices.
You’ve probably heard of Cyanogen
and CVPCS if you are at all involved in the
community. They are, in fact, a couple of the
most influential developers of CyanogenMod,
an open-source customized version of
Android—a distribution of sorts. With this
distro, you get the kernel for your device as
well as the latest version of Android.
Before I begin, the most important
requirement is that you are rooted. You can
find many guides on-line to do this. Once
you obtain root, let’s begin with the tweaks.
Android comes with the Linux kernel,
which, if you have not already inferred,
means that many of the mainline kernel
tweaks can be applied to the Android
version of the kernel through the use of
various configuration files. For this guide,
you’re going to edit build.prop, which is
located under /system, and the local.prop,
which is under /data.
On Linux, you can edit these files with vim
or nano, but Android is slightly different.
On Android, you need a file browser that is
able to run and edit files as the superuser or
root. There are many root-level browsers on
the Android market, but I have been quite
successful with an application called Root
Explorer, so I use that for the remainder of
this guide, but any root browser with text
editor support will suffice.
Now that you have rooted your device
and have the version of Android installed
that you want to tweak, you can begin
tweaking. The first thing I normally do
is optimize my TCP stack for faster 3G
download speeds. To do this, open your file
browser of choice (I used Root Explorer),
navigate to /system/build.prop or /data/
local.prop, and open it in the text editor.
Every Android device has a build.prop file,
but not all will have the local.prop file. If the
local.prop file exists, it’s generally safer to edit
this file rather than the build.prop file. So edit
whichever you feel safer editing, and copy the
code below into your file of choice:
ro.ril.hsxpa=2
ro.ril.gprsclass=12
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ro.ril.enable.fd.plmn.
script from the terminal, su to root, then
navigate to where you downloaded it to
your SD card and run it. To run it from
a script manager, again navigate to the
directory where it is located, and run it as
root. It will ask you which scrolling speed
you prefer, so select one. Next, the V8/V6
script will present you with 14 different
options from which to choose. I like to
multitask without my applications forcibly
closing, so I choose option 7, but there also
are options for gaming, aggressive memory
management and balanced management.
It’s that simple. Happy tweaking!
prefix=23402,23410,23411
—JAMES COYNER
ro.ril.hep=1
ro.ril.enable.dtm=1
ro.ril.hsdpa.category=28
ro.ril.enable.a53=1
ro.ril.enable.a52=1
ro.ril.enable.3g.prefix=1
ro.ril.htcmaskw1.bitmask=4294967295
ro.ril.htcmaskw1=14449
ro.ril.hsupa.category=9
ro.ril.def.agps.mode=2
ro.ril.def.agps.feature=1
ro.ril.enable.sdr=1
ro.ril.enable.gea3=1
I generally tend to add my tweaks of
preference to the local.prop file, but after you
edit it, reboot your device and enjoy the faster
download and browsing speeds. This method
is generally the more difficult of the two
methods that are available. The easiest way to
apply tweaks is to do it with a script. To run a
script on Android, you can, in fact, run your
script of choice exactly the same as you do on
your Linux desktop, through the terminal.
Two scripts that I now use to accomplish
the above are the V8/V6 Supercharge
and 3G Turbocharger scripts. The V8/V6
script modifies how Android manages the
available system memory as well as various
kernel tweaks to provide a smoother and
more fluid Android experience. A simple
Web search will help you find both of
these scripts. You can run these scripts in
either of two ways: through the terminal
application or a script manager. To run the
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WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 23
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[
UPFRONT
]
Elmer for PDEs
Elmer is an open-source multiphysics
simulation software that has been around
since 1995. It is developed by the CSC —
IT Center for Science Ltd. This group is
administered by the Ministry of Education,
Science and Culture in Finland. With Elmer,
you can model physical systems, such as
fluid dynamics, electromagnetism, heat
transfer and acoustics. All of those problem
areas have one thing in common—they
are all described by partial differential
equations (PDEs).
A PDE is a differential equation that
depends on more than one variable,
usually more than one space variable.
For example, an equation that describes
how heat gets transferred across a metal
plate, where a is the thermal diffusivity
of the metal plate, would look like the
formula shown in Figure 1.
volume and finite difference methods.
Elmer uses the finite element method.
The basic idea is to break up the problem
space into some kind of a mesh of smaller
spaces, and then either eliminate the
PDE completely, by reworking it into a
steady state problem on the mesh, or
approximating the PDE with a system of
ordinary differential equations that then
are integrated using standard methods,
like Euler’s method or Runge-Kutta.
Elmer is distributed under the GPL, so
you always can download the source and
compile your very own version. Binaries
are available for all those poor users still
stuck on Windows. Packages should be
available for most Linux distributions. For
Ubuntu-based distros, you simply can use
the following to install Elmer and all the
necessary libraries:
sudo apt-get install elmer
Figure 1. Sample Equation
Very simple PDEs have exact solutions,
but anything more complex that describes
more physical situations just can’t be
solved exactly. This is where numerical
solutions come into play. There are three
widely used methods: finite element, finite
Elmer is broken into several parts.
ElmerSolver is the part that actually takes
the input files and does the calculations
to evolve the PDE you are interested in.
ElmerPost is the visualization and postprocessing tool. With this tool, you actually
can see the results of your calculations.
ElmerGrid is the meshing tool that can
create simple 1-D, 2-D and 3-D meshes that
will be used to evolve your PDE. It also can
be used to import meshes generated using
other software packages, such as those
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created using the Ansys tools.
There also is a GUI interface called
ElmerGUI. ElmerGUI allows you to define
and generate input files for ElmerSolver, as
well as import external meshes from other
software (Figure 2).
Figure 2. ElmerGUI
Looking at all of this, you may be
thinking, “This is perfect!” So, I also should
mention some of Elmer’s downsides. Elmer
actually is a suite of tools, and those tools
are not always at the same development
level. The documentation tends to lag
behind the newest features, and ElmerGUI
may be missing some of the more esoteric
methods and models that ElmerSolver
can use. Elmer is a huge system, and
like any large software package, it has a
steep learning curve. The tools available
(ElmerGrid) can handle generating only
relatively simple meshes. This means that
if you have a very complicated system,
you likely will need to use some other tool
to generate the mesh and then import it
into Elmer. If you can work around these
possible deficiencies, Elmer may be exactly
the right solution for you.
ElmerGUI is likely to be what most people
prefer using. You can import element
mesh files in various formats, generate
element partitionings for geometry input
files, set up the PDE systems you want to
solve, and export model data to hand in to
ElmerSolver. Most conveniently, ElmerGui
also provides an interface to the parallel
version of the solver, ElmerSolver.mpi. There
also is a built-in post-processor that allows
you to view your results right there from
ElmerGUI. The menus in ElmerGUI are fully
programmable as well, so you can tune the
interface to match your specific problem
area better.
A user forum, wiki and other resources
are available at http://www.elmerfem.org,
and a very good tutorial is available from
the main Elmer Web site (http://www.csc.fi/
english/pages/elmer). Along with the
tutorial documentation, sample files are
available for each of the cases. Those
files can be great starting points for your
own calculations and help you as you are
learning the system. As an example, let’s
look at the sample “Computation of fringe
capacitance”. Once you have downloaded
the sample files and unpacked them,
you can load the project with File→Load
Project... from the menu. Once it is
loaded, all the input data also is loaded.
A project is simply a directory containing
all the files required to do a computation.
The actual mesh is defined by the files
mesh.header, mesh.nodes, mesh.elements
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[
UPFRONT
]
Figure 3. Solver Input File
Run→Postprocessor (VTK)...
(Figure 5).
As you can see, several
tools are available to help
you visualize the results of
your calculation.
Now that you have seen a
basic example of running one
of the tutorials, what else can
Elmer do for you? The solver
can handle solving linear
systems. It can do this by using
direct methods, through the
LAPACK library, for example.
You can use a set of Krylov subspace
methods to do iterative solutions. In
order to get rapid convergence though,
you usually need to use some form of
preconditioning. A class of iterative
methods called multilevel methods
are used for large linear systems.
Elmer provides two options: geometric
multigrid and algebraic multigrid.
More complex, and hence more
and mesh.boundary. The current settings
and state are stored in the file egproject.xml.
There also is a solver input file called
case.sif that is handed in to ElmerSolver
when you actually are ready to do your
calculations. You can edit this file via
Sif→Edit... (Figure 3).
You can edit the model details (like
physical constants) via Model→Setup....
When you are ready to run your
calculation, you can use
Run→Start Solver. This opens
a log window and shows
its progress. A convergence
monitor shows how quickly
Elmer converges on the results
(Figure 4).
This creates a new file
named case.ep in your project
directory containing the
results of your calculation.
You can view it using either
Run→Start Postprocessor or
Figure 4. Convergence Monitor
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Figure 5. Viewing the Results
physically accurate, problems tend to
be nonlinear. This nonlinearity may be
as simple as what you see in the full
equation for pendulum motion to the
Navier-Stokes equations for fluid flow to
the equations of General Relativity. Elmer
deals with nonlinear systems by first
linearizing the equations at each iteration
step. How the equations are linearized
depends on exactly which solver method
is being used. For example, the NavierStokes solver can use either the Picard
linearization or the Newton linearization.
There are methods for solving timedependent systems. First-order time
derivatives can be discretized using
either the Crank-Nicolson method or
the Backward Differences Formulae. You
also can solve eigenvalue problems with
Elmer. These tend to crop up in structural
analysis problems, including factors like
elasticity and damping.
For really large problems, you likely
will want to look into running your
computation in parallel. Elmer
uses MPI as the parallelization
technique, along with domain
decomposition as the method
of dividing up the work. The
first step is to take the mesh
and subdivide it into chunks or
partitions, which, depending
on the actual calculation to
perform, will divide the load
evenly across all the CPUs.
These chunks then are sent
out to individual CPUs, and
the calculation is done. At the end of
the run, the results are combined back
into a single result. Because of the work
involved in partitioning and so forth,
most users likely will take advantage of
ElmerGUI’s parallelization tool.
The last of Elmer’s selling points is its
modular nature. The solver is written in
FORTRAN 90. This means if you want to
add your own user functions or a complete
solver, it is simply a matter of writing
a FORTRAN module and including it in
Elmer. The main Elmer site provides good
documentation covering the steps involved.
Hopefully, this introduction has given
you some ideas of what you can do with
Elmer. If you are studying multiphysics
problems, Elmer probably is a very good
tool to learn. It also might be a good
tool to introduce in a numerical physics
course, because you can model so much.
If you do end up using it in your research
or studies, I would love to hear about it.
—JOEY BERNARD
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2011 Book
Roundup
REUVEN M.
LERNER
Reuven’s annual list of recommended books and podcasts for
open-source developers.
Each year, I like to step back and write an
article describing and recommending some
of the computer-related books I have most
enjoyed during the previous 12 months. I’m
fortunate to come across a very wide variety
of books, as well as journals and podcasts,
and I enjoy sharing the best of what I’ve
found. I believe that everyone in our industry
should try to keep their skills up to speed not
only by practicing software development, but
also by learning more about it.
My rules for these reviews are pretty
simple. If I discovered and read a book
during the past 12 months or so, it’s fair
game for me to mention it. It’s possible
that some of the books I discuss here
were written and published long ago,
but if it’s new to me, I include it. I don’t
promise to be comprehensive. I can judge
only the books that came my way. And, I
obviously have my favorite technologies,
which tend to get more of my attention.
Ruby and Rails
Ruby continues to be my favorite
programming language, one I use
every day, and it pleasantly continues
to surprise me. Much of my work in
Ruby is as a Web developer, using the
Ruby on Rails framework. I do share
the concerns some have expressed—
that Rails is becoming too complicated
for newcomers, in part because of its
adoption of many new, unusual or Railsspecific technologies in recent versions.
However, I still think that if you’re writing
a Web application, you would be wise at
least to consider Ruby on Rails.
I’m not the only person who feels
this way, which is why a torrent of Ruby
books continues to be published. One
of the best I’ve seen in the past year is
Eloquent Ruby by Russ Olsen (AddisonWesley, ISBN 978-0321584106). This book
is aimed at intermediate-to-advanced
Ruby programmers who want to write
code that’s not only functional, but also
takes advantage of the language’s best
characteristics. Some of the techniques are a
bit advanced, but I’m all in favor of learning
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such techniques, even if I never use them,
because they deepen my understanding
of the language. This book has deservedly
received a great deal of praise.
For people new to Ruby and who want
to learn how to develop Web applications
using Rails, Michael Hartl has produced a
book, “Ruby on Rails 3 Tutorial” (AddisonWesley, ISBN 978-0321743121) and an
accompanying video. I must admit I haven’t
yet watched the video, but the book is a
great introduction to the environment,
spirit and techniques of Rails development.
The book has the attitude that you can
learn the Ruby language while you’re also
learning Rails, and although I think that a
better foundation probably is appropriate
before jumping into Web development, it’s
far from a fatal flaw. The book, which is
aimed explicitly at beginners, is full of useful
tidbits and hints on Ruby, includes hosting
an application on Heroku, and also is about
Rails and Web development in general.
One of the first books about Ruby to be
published is The Ruby Way by Hal Fulton,
and a second edition was published several
years ago. In the wake of this success,
Obie Fernandez published The Rails Way,
an almost encyclopedic description of
Ruby on Rails and the way it can (and
should) be used. This past year, Fernandez
published an updated version of this book,
The Rails 3 Way (Addison-Wesley, ISBN
978-0321601667), and although there are
many improvements and interesting tidbits
in this book, it’s no longer as extensive
and encyclopedic as the previous edition.
Now, that’s not necessarily a bad thing,
given that Fernandez is well known in the
Rails community, and he’s trying to show
what technologies he uses, as opposed to
the ones that others might use. That said,
I learn something new every time I read
through this book, typically saving me time
in the future. So, I recommend that Rails
developers read this book, but only after
they’ve had sufficient grounding in Rails.
Two more books, both from the
Pragmatic Programmers, are worth a look
for Rails developers: Continuous Testing
with Ruby by Ben Rady and Rod Coffin
(ISBN 978-1934356708) gives a step-bystep introduction to the world of automated
testing and how you can incorporate it
into your Ruby development environment.
Meanwhile, Jose Valim, author of the
popular “Devise” gem for authentication in
Rails, has written Crafting Rails Applications
(ISBN 978-1934356739), which is less an
introduction to Rails applications than a
tour of interesting projects you can do
with Rails, using advanced techniques that
might well come in handy.
Finally, I read at least two nice
short, independently published books
during the past year. Rails 3 Upgrade
Handbook by Jeremy McAnally
(http://www.railsupgradehandbook.com)
is a short but extremely useful guide to
moving your Rails applications from version
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It seems I’m not the only programmer
whose feelings about JavaScript have
changed dramatically during the years.
2 to version 3.
If you haven’t yet made this change,
McAnally walks you through many of the
necessary steps to get it done. Separately,
Avdi Grimm, an independent developer,
blogger and podcaster, published a
great little book about exceptions and
how to use them called Exceptional Ruby
(http://exceptionalruby.com). Unless
you’re thoroughly schooled in the way
Ruby exceptions work, this is a great book
to read through, understand and then put
into practice in your own projects.
JavaScript
It seems I’m not the only programmer
whose feelings about JavaScript have
changed dramatically during the years.
First, I dismissed it as a toy language that
wasn’t good for much. Next, I cursed it
every time I had to deal with it, because
of the strange syntax and conditions, and
then I cursed the implementations of the
language, which were slow, buggy and
incompatible with one another. Then,
almost overnight, JavaScript changed—or
at least, my attitude toward it did. The
differences between browsers were easily
ignored, thanks to libraries like Prototype
and jQuery. Bugs were fixed, and JavaScript
engines were tuned and re-tuned, making
it a very fast-executing language. And
libraries grew over time, such that you now
can do amazing things with JavaScript. I
still find the language to be a bit verbose
and annoying in some ways, but there’s
no doubt that JavaScript development
is an integral part of any modern Web
developer’s toolbox, and understanding
the way it works is essential.
Two great books that can help push
you forward are Eloquent JavaScript by
Marijn Haverbeke (ISBN 978-1593272821,
and at http://eloquentjavascript.net),
which introduces programming at a
basic level, but does so by showing many
powerful and interesting techniques
JavaScript has to offer. Even if you’re a
seasoned JavaScript hacker, it’s worth
looking at this book. A nice thing about
the on-line edition, available for free at
the URL listed above, is that you can run
the code right in your browser. I’ve also
seen many mentions of the JavaScript
Cookbook by Shelley Powers (O’Reilly, ISBN
978-0596806132). It doesn’t aim to be a
JavaScript tutorial, but rather a collection
of short techniques, ideas and articles
describing common tasks that JavaScript
coders might need. If you’re using
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JavaScript—and nearly all Web developers
are doing so nowadays—you probably will
get a lot out of this book.
Now that JavaScript executes so quickly
and is universally available in browsers,
we’ve seen the beginning of two new
trends: Web frameworks that operate
within the browser, using only JavaScript,
and languages that compile into JavaScript,
rather than into byte code or binary
executables. For now, the only reference to
Backbone.js that I have seen is a screencast
from Peepcode (https://peepcode.com/
products/backbone-js), which I enjoyed
and from which I learned quite a bit.
Meanwhile, if you’re interested in trying
CoffeeScript—a language that compiles
into JavaScript, which is mandatory in Rails
3.1, and which has taken the JavaScript
world by storm—you probably should read
Trevor Burnham’s CoffeeScript: Accelerated
JavaScript Development (Pragmatic
Programmers, ISBN 978-1934356784),
which introduces the language and
describes how you can use it.
Other Technologies
Although my main language is Ruby, I still
like and appreciate Python quite a bit, and
I still get to use it in some of my projects.
Mark Lutz, who has written many editions
of Learning Python and Programming
Python for O’Reilly has come out with
his latest book, Programming Python
4th edition (ISBN 978-0-596-15810-1). If
you’re using Python, you probably want to
have this book on your shelf, so that you
can refer to it on a regular basis. Moreadvanced Python programmers would do
well to read Pro Python (Apress, ISBN 9781430227571), which describes the behindthe-scenes implementation of many Python
idioms, such as metaclasses and common
protocols, which really can come in handy.
HTML and CSS form the foundation of
the Web, and HTML5 includes so many new
features that learning them can take some
time. From the Pragmatic Programmers comes
HTML5 and CSS3 by Brian Hogan. This book
is written well, providing (I think) a gentler
introduction to the subject than many other
books. Another great introduction, but one
that focuses on other aspects of HTML5,
is Mark Pilgrim’s on-line Dive into HTML5
(http://diveintohtml5.org), also available
as a print book, HTML5: Up and Running
(O’Reilly, 978-0596806026).
Regular readers of my articles know
that I have long used PostgreSQL for all of
my relational database needs. Although I
believe that PostgreSQL is a better fit for
most projects than MySQL and offers a
powerful host of features that is a serious
match for open-source and commercial
databases alike, it’s a sad fact that there
aren’t very many books about PostgreSQL
on the market. Fortunately, Packt Press has
released two very high-quality books in
the past year: PostgreSQL 9 Administration
Cookbook by Simon Riggs and Hannu
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Krosing (ISBN 978-1849510288) and
PostgreSQL 9.0 High Performance by
Gregory Smith (ISBN 978-1849510301).
I personally refer to these books all the
time when working on clients’ projects,
and I always learn something from them.
Other Languages
Lisp is one of those languages that people
either swoon over and dream about or
despise with a passion. I’m strongly in the
first category, and, thus, I continue to enjoy
the fact that Lisp books still are published. A
hilarious and excellent introduction to Lisp,
Land of Lisp, teaches Lisp programming and
concepts by writing games. I really enjoyed
reading this book, and I think it’s worth the
time even if you don’t write programs or
plan to develop in Lisp.
I’m still working my way through it, but
I want to mention Learn You a Haskell
for Great Good! (No Starch Press, ISBN
978-1593272838), which is both funny and
interesting, and it finally has managed to
keep my attention for a while on learning
Haskell. I’m not sure if I’ll ever use Haskell
in a real project, but I feel like at least
I’m in a better position to understand its
strengths and weaknesses.
R is a statistics language that I’ve been
using for many years, and it seems to be
getting more popular over time. O’Reilly
has published the R Cookbook (ISBN 9780596809157), which, in contrast to the
many free books available on-line, takes a
very practical approach to doing things in
R, whose data types and functions are a bit
different from other languages I’ve used.
Podcasts
I’ve become quite a fan of podcasts during
the past few years, in part because I tend
to sit on the train a great deal, as well as
walk to clients’ offices from the nearest
train stop, which isn’t always nearby!
Fortunately, many high-quality, interesting
podcasts exist—far more than I have time
to listen to. I’m listing here those that
have to do with open-source and Web
development; obviously many others are
available on-line on a variety of other
interesting topics.
Two of my staples are done by the pair
of Jason Seifer and Peter Cooper: “The
Ruby Show” (http://rubyshow.com) and
its younger sibling “The JavaScript Show”
(http://javascriptshow.com) are half-hour,
weekly news updates on the state of each
of these languages and the development
frameworks built on them. I imagine their
humor is not for everyone, but I find Jason and
Peter to be entertaining as well as informative,
and regret when they (or I) miss a week.
Another good open-source podcast is the
“Changelog” (http://thechangelog.com),
a weekly hour-long interview podcast hosted
by Adam Stacoviak and Wynn Netherland.
Finally, one of the most thought-provoking
and interesting podcasts I’ve started to listen
to is “Ruby Rogues” hosted by Charles
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Max Wood (http://rubyrogues.com) with
a panel of distinguished Rubyists every
week. Now, it’s true that the panel comes
from the Ruby world, and the discussion
centers around the Ruby language, but the
panelists are serious and clever software
engineers who take pride in their craft and
always are learning how to do things better,
which means the discussion is deeper than
most other blogs and podcasts I follow. If
you’re interested in hearing how truly great
software engineers think, this is a great
weekly one-hour dose.
Non-Computer Books
It’s true that I tend to read a great many
computer-related books during the year,
but I’m happy to report that I read about
other subjects as well. Two of the most
interesting books I’ve read in the past
year are Country Driving by Peter Hessler
(ISBN 978-0061804090), the former China
correspondent for the New Yorker, who
provides an interesting and nuanced picture
of modern China.
Another book about that area of the
world, which was haunting and disturbing
more than anything else, was Nothing
to Envy by Barbara Demick (ISBN 9780385523912), in which she describes what
life is like in North Korea. The stories she
tells in this book, based on interviews with
North Koreans who escaped, are beautifully
told but horrifying to read all the same.
I also read two books by Gail Collins,
the New York Times columnist, about
the history of women in America: When
Everything Changed (covering the 1960s
through the present) and America’s Women
(ISBN 978-0060185107), describing the
history of the United States from colonial
times through the 1960s, but from a
woman’s perspective.
Finally, I’m currently in the middle of
How Rome Fell by Adrian Goldsworthy
(ISBN 978-0300137194). My high-school
history classes didn’t go into much detail
on most subjects, and I’m learning through
this book just how much I don’t know
about an empire that ruled the part of the
world in which I currently live, and whose
influence still can be felt today by a very
large number of people. Although the book
is about how the Roman empire fell, I’m
using it as a way to better understand how
it worked when it did, and I’m enjoying
having that opportunity.
I’m sure I could recommend many other
books, but these were the first that came
to mind. My next article will return to our
regularly scheduled program, looking more
at open-source Web technologies that can
help us put the ideas from these books into
practice for ourselves and our clients.■
Reuven M. Lerner is a longtime Web developer, architect and
trainer. He is a PhD candidate in learning sciences at Northwestern
University, researching the design and analysis of collaborative
on-line communities. Reuven lives with his wife and three
children in Modi’in, Israel.
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Working with
Image Files, Part II
DAVE TAYLOR
Adding caption generation to the image-inclusion script.
If you’re a faithful reader of my LJ column
with a good memory, you’ll have realized
this is the second time I’ve written a set
of columns talking about my imagescaling script. My last article presented a
major revision to the script that added the
capability of scaling the image dimensions
in the resultant HTML code and also warning
if it produces a significantly smaller image
than the existing file specifies.
One thing I pay close attention to
with my Web sites is their search-engine
friendliness. After all, why put all the
effort into producing good content and
then omit the last step or two that can
help maximize search-engine results
placement (SERPs, in the biz)?
It turns out that if your page loads
slowly, you’re less likely to nab a really
great spot in the search results than if
it’s lightning fast. So, if you are loading a
73KB image and scaling it down 33%, for
example, it’d be faster to scale the image
file itself (even if you end up with multiple
versions of the image at different sizes)
and have the 39KB version or similar.
In this article, I want to turn our attention to
something else, generating attractive captions.
There are two ways that captions are specified
from the command line: -c tells the script to
use the filename as the caption, substituting
spaces for dash (-) or underscore (_)
characters, and -C xx tells the script to use
the user-specified value xx for the caption.
The latter is more accurate, but more
work, so I typically use -c, particularly
if I’m generating the image-inclusion
HTML for a group or collection of images
en masse. In that case, the filename is
typically something like “mac-pageshyphenation-control-1.png”.
Converting Filenames to Image Captions
The easy way to create a caption is to axe
the filename suffix and replace all dashes
or underscores with spaces. For the
filename mentioned above, that’d give
us “mac pages hyphenation control 1”,
which isn’t too bad. However, it would
be better to fix the capitalization so the
caption looks more like proper English.
The problem is, case-transliteration
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utilities in Linux are designed to be allor-nothing enterprises, so translating
“pages” into “PAGES” is easy, but
producing “Pages” is a bit trickier.
To do that, the script breaks the alllowercase caption into separate words,
then breaks each word into its first letter
and subsequent letters:
example, “The Black and the Blue” is
correct, not “the Black and the Blue”.
One problem needs to be fixed due
to how I reassemble the sentence in the
script: the removal of the final trailing
space. There are a bunch of ways to do
that, but I really like using rev twice and
cutting off the very first character:
firstletter=$(echo $word | cut -c1 |
rev | cut -c1- | rev
tr '[[:lower:]]' '[[:upper:]]')
newcaption="$newcaption$firstletter$otherletters "
The entire function is neatly wrapped in
a shell function:
Wrapped in the following for loop:
FixCaption()
otherletters=$(echo $word | cut -c2-)
{
for word in $nicecaption
newcaption="" ; wordcount=0
for word in $nicecaption
Ideally though, the sentence cap
function should be smart enough to
know that certain words shouldn’t be
capitalized, like “the”, “of” and “or”.
That I solve as generically as possible:
do
if [ $wordcount -gt 0 ] ; then
case $word in
the|and|or|a|an|of|in) newcaption="$newcaption$word ";
continue; ;;
esac
if [ $wordcount -gt 0 ] ; then
fi
case $word in
firstletter=$(echo $word | cut -c1 | tr '[[:lower:]]'
the|and|or|a|an|of|in) newcaption="$newcaption$word ";
Continue;
'[[:upper:]]')
;;
otherletters=$(echo $word | cut -c2-)
esac
newcaption="$newcaption$firstletter$otherletters "
Fi
wordcount=$(( $wordcount + 1 ))
done
Do you know why I check the word
count in the resultant properly capitalized
caption? Because if it’s the first word in
the caption, it should be capitalized. For
nicecaption=$(echo $newcaption | rev | cut -c1- | rev)
}
It’s complicated, but hopefully,
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still understandable!
Producing Good HTML Code
Are you wondering what we’ve created?
Here’s how this now gives us a nice, readable
caption based on the well-named file:
$ scale -c 1 facebook-upload-photo-computer-1.png
<center><img
src="http://www.askdavetaylor.com/pics/
➥facebook-upload-photo-computer-1.png"
alt="facebook upload photo computer 1" border="0"
➥width="604" height="204"/><div style="font-size:
➥80%;color:#777;">Facebook Upload Photo Computer
➥1</div></center>
I’ll unwrap that so you can see the HTML
with less headache:
<center>
<img
src="http://www.askdavetaylor.com/pics/
➥facebook-upload-photo-computer-1.png"
alt="facebook upload photo computer 1" border="0"
➥width="604" height="204"
If you know HTML, you might be
tempted to have some better code, where
the entire image + caption are in a single
div container. For that matter, there’s a
“caption” attribute to the “img” tag in
modern HTML, but I don’t use it because
I like to have more control over how the
actual text is positioned and rendered on
the page—old-school, I guess.
I’m going to stop hacking the script
here because it’s already almost 200
lines, and I have to say that if a script is
getting to be more than 100 lines or so,
it might be time to consider moving the
functionality into a Perl script or another
programming language like C or C++.
Not always, but shell scripts are really
good until a certain point, then you’re
just wrestling with limitations rather than
expanding your capabilities.
That’s it for this month. Do you have
a scripting challenge you’d like some
help with or just an idea for a fun or
interesting project we can tackle here in
Linux Journal? If so, get off your duff and
send me a message about it! ■
/>
<div style="font-size:80%;color:#777;">
Facebook Upload Photo Computer 1
Dave Taylor has been hacking shell scripts for a really long time,
30 years. He’s the author of the popular Wicked Cool Shell Scripts
and can be found on Twitter as @DaveTaylor and more generally
at http://www.DaveTaylorOnline.com.
</div>
</center>
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Automatically
Lock Your Computer
KYLE RANKIN
Your phone can do much more than make calls and install apps
that make obnoxious noises—learn how you can use it to lock
your screen automatically.
If you’ve ever worked with pranksters,
you’ve probably come across this classic
office prank. First, the unsuspecting victim
leaves his computer and goes to lunch or a
long meeting and doesn’t lock his screen.
The prankster then takes a screenshot of his
current desktop, hides all the desktop icons
and any taskbars, and sets the background
to be the screenshot the prankster just
took. When the victim gets back to his
computer, none of the icons work, and no
programs will open, yet when he inevitably
reboots, even that doesn’t fix it. Around
the time he calls the desktop support team,
the prank is revealed and everyone has a
good laugh about it—except maybe the
victim, who vows from that day on always
to lock his screen.
Good Locks Make Good Neighbors
I don’t know about you, but even though
I’ve never been the victim of a prank like
that, I’ve always tried to be good about
locking my screen when I’m away. I imagine
some of this just stems from trying to be
thoughtful about security, but also, if you
are a sysadmin, you often have access
to a lot of sensitive systems and data.
Although you’d like to extend trust to your
coworkers, an unlocked sysadmin computer
would be a great source for sensitive
information if you were a disgruntled
employee. In this article, I discuss a simple
program I’ve found that works great to
lock your screen automatically when you
walk away. At the end of the article, I also
discuss some ideas for how to hack in to a
system protected by this software.
Traditionally on any desktop environment
I’ve used, I would configure a Ctrl-Alt
L keybinding that locked my screen. It
was so committed to muscle memory,
that the moment I was about to stand
up, my fingers automatically would lock
my desktop without thinking about it.
Although this method works great, I’ve
recently discovered just how easy it is to
set up your desktop to lock automatically
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when you leave, and even better, to unlock
automatically when you return.
The solution to proximity-based desktop
locking has been around for a while. I
remember Linux Journal’s own Bill Childers
demonstrating such a thing to me with
Bluetooth on a Mac more than six years
ago, but I’ve never felt like messing around
with the Bluez tools on Linux to write my
own script. It turns out these days there’s
a simple program you can use to lock your
screen via Bluetooth that takes only a
minute to set up: BlueProximity.
How BlueProximity Works
Essentially, BlueProximity works on the
notion that most of us carry around a
Bluetooth device with us—our cell phone.
Because Bluetooth works only over a
limited range, with a bit of tuning, you can
make some assumptions about how close
a device is to your computer based on the
strength of its signal. BlueProximity works
via these assumptions to decide when to
lock or unlock your screen. When you leave
your computer, the Bluetooth signal gets
weaker until it crosses a threshold, and
your desktop is locked. When you return
to your computer, the signal gets stronger
until it crosses a different threshold, and
the computer automatically unlocks.
Install BlueProximity
You install BlueProximity much like any
other Linux program: with your package
manager. In my case, the package simply
was called blueproximity. Alternatively, if
your distribution doesn’t package it, you
can download and build the software from
the source available at the BlueProximity
SourceForge page. Once installed, you
either can type blueproximity in a
terminal to launch the program or click
on it in your applications menu (on my
system, it showed up under the Accessories
category).
Once you start the program, you will get
a new icon in your panel and also see a
window much like the one shown in Figure
1. BlueProximity requires that the device you
set up already has been paired with your
computer, so if you haven’t yet paired your
Figure 1. The Default BlueProximity Tab
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phone (or other Bluetooth device you wish to
use), you need to go through the steps to pair
your Bluetooth device first. In my case (on an
Ubuntu system), I first made sure Bluetooth
was enabled and visible on my phone, next I
clicked System→Preferences→Bluetooth, then
clicked Set up new device, and after that I just
followed through the wizard that appeared.
After you pair the Bluetooth device, go
back to the main BlueProximity screen and
click on Scan for devices. It may take a bit
for the scan to complete, but afterward,
you should see your Bluetooth device on
the list. At that point, just select it, click
Use selected device, and your device will be
configured and ready to use. You can safely
click the close button at the bottom of the
window, as BlueProximity will still stay in
your panel.
Fine-Tune Your Settings
Out of the box, BlueProximity tries to use
reasonable settings to determine when to
lock your screen; however, each Bluetooth
device is different, and I’ve personally seen
that different Bluetooth devices can have
much different antenna strengths. If you
notice that your screen doesn’t lock as soon
as you’d like, or worse, if it locks while you
are still at your desk, click on the Proximity
Details tab where you can edit thresholds
(Figure 2). In this window, you will find a
number of different sliders. The Distance
slider for both Locking and Unlocking lets
you control how close you need to be to the
computer. The Measured atm slider updates
every second or so and shows the current
Figure 2. The Proximity Details Tab
distance BlueProximity reads, so you can get
a sense of how sensitive your equipment is.
The Duration sliders let you control how long
the device needs to be at a certain distance
before it locks or unlocks the screen. This is
useful in particular when tuning the Locking
section so that one bad reading doesn’t lock
your screen when you don’t want it to.
If you do notice that the screen locks
on you often while you are at your desk,
increase the Distance slider for locking.
Alternatively, if you notice when you come
back to your desk you have to sit there for
some time before it unlocks, you may want
to increase the Distance slider for Unlocking
and decrease the Duration slider if it’s
higher than one. Just make sure that your
unlocking distance isn’t higher than your
locking distance.
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Use Your Own Locking Program
By default, BlueProximity is configured to
trigger gnome-screensaver commands. If
you use GNOME, that might be fine, but
if you use another desktop environment,
click the Locking tab (Figure 3) where
you can change what command gets
run to lock and unlock the screen. By
default, you can choose between gnomescreensaver and xscreensaver from the
drop-down list, but you could really put
any script you want in here. For instance,
you might want to create a locking
bash script that not only calls gnomescreensaver but also uses a DBUS signal to
pause your music. Then you could write a
LJ211-November2011.indd 43
Figure 3. The Locking Tab
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It is this convenience that may possibly open
you up to an attack.
similar script to unpause your music and
unlock the screen when you return.
Hack BlueProximity
Security is often a trade-off for
convenience. BlueProximity is interesting
in that it tries to increase your security (by
automatically locking your screen), and
it also tries to increase your convenience
(by automatically unlocking your screen
when you return). It is this convenience
that may possibly open you up to an
attack. That said, BlueProximity and the
Bluetooth protocol do make attacking
this method rather difficult, because
BlueProximity allows only one device to
unlock it at a time. You may think you
could hack this setup simply by cloning
the MAC address of a person’s phone
on your Bluetooth device. Although this
is possible, unfortunately, during the
pairing process, keys are shared between
the two devices that they will use for
secure communication later on, so even
if you can clone a phone’s MAC address,
it still will not necessarily accept your
device, because you don’t have the shared
secret. That having been said, Andrew
Y. Lindell released a paper for Blackhat
2008 demonstrating that if you could
sniff the pairing procedure, the password
potentially could be leaked to you. Even if
you weren’t there when the devices were
paired, the paper demonstrated how you
might be able to get a device to re-run
the pairing procedure.
Of course, such an attack is quite
sophisticated and might be difficult to pull
off. An easier approach simply would be
to borrow the person’s phone to make a
phone call or check out an app when he
isn’t at his desk and then sneak over there.
Along with that attack, BlueProximity
naturally would be vulnerable to knocking
the person out and stealing the phone, but
then we are talking about office security
here, and if you have to worry about
coworkers beating you over the head and
robbing you, maybe you should look into
another line of work.■
Kyle Rankin is a Sr. Systems Administrator in the San Francisco
Bay Area and the author of a number of books, including The
Official Ubuntu Server Book, Knoppix Hacks and Ubuntu Hacks.
He is currently the president of the North Bay Linux Users’ Group.
Resources
The BlueProximity Project Page:
http://sourceforge.net/projects/blueproximity
Blackhat 2008 paper on Bluetooth Hacking by
Andrew Y. Lindell: http://www.blackhat.com/
presentations/bh-usa-08/Lindell/BH_US_08_
Lindell_Bluetooth_2.1_New_Vulnerabilities.pdf
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LINUX JOURNAL
on your
e-Reader
FREE
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Subscribers
Customized Kindle and Nook
editions now available
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LJ211-November2011.indd 45
10/21/11 9:34 AM
NEW PRODUCTS
Protecode System 4
The most noteworthy enhancement
in the upgraded Protecode System
4, Protecode Inc.’s open-source
license management solution, is full
support for the Software Package
Data Exchange (SPDX) standard.
Sponsored by the Linux Foundation,
SPDX is an effort to create a
standard format for communicating
the components, licenses and copyrights associated with a software package. Protecode
says that System 4’s ability to read and generate SPDX information eases license information
exchange across the software supply chain and allows for a simpler license compliance
process. System 4 now also includes Code Administrator, an application that facilitates
requesting, analysis and approval of open-source and other third-party software within an
organization. It ensures that only a well-understood, preapproved set of software packages
of specific versions with defined use cases are deployed.
http://www.protecode.com
Nimbula Director
Nimbula has unveiled the new version 1.5 of Nimbula Director, which the
company says is the first cloud operating system that’s capable of supporting
a geographically distributed cloud. Nimbula Director helps enterprises and
service providers build powerful private, hybrid and public cloud infrastructures.
Nimbula Director abstracts the underlying technology to present a coherent view
of a completely automated compute and storage cloud. This one-stop virtual
data-center management solution isolates customers from the operational and
hardware complexity associated with deploying a private or public cloud. The
software can manage many geographic locations of a multi-site cloud from a
single view, which allows end users to access any resource worldwide and deploy
their workloads to any site in a self-service manner with a single login.
http://www.nimbula.com
46 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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NEW PRODUCTS
Akiri Solutions’ DevBox-EZ
Cheap is good, but free is better, and the
latter is what you’ll pay for Akiri Solutions’
DevBox-EZ, a new virtual appliance that offers all
the tools necessary for implementing software
development projects as well as simplifying
and accelerating the migration to Git. The free
version is modeled on Akiri’s popular DevBox
solution. DevBox-EZ, says its developer, “is up
and running within just a few minutes and
provides shared Git repositories, bug tracking, automated backup, file sharing and projectbased built-in wikis”. Integrated bug and issue tracking eliminates the need for the hassle
of a separate tool. The automated backup can be scheduled at any time with a click of the
mouse, and project-based built-in wikis that help ensure important project knowledge can
be captured easily. The file-sharing capability simplifies the painstaking process of adding or
deleting users and managing permissions versus using FTP sites or shared file servers.
http://www.akirisolutions.com
Samba
Messrs. Tridgell, Allison and the rest of the dedicated Samba team have been
forging ahead with a slew of new features and functionality, culminating
in a recent major new version 3.6 release. Samba, of course, is the famed
Windows interoperability suite of programs for Linux and UNIX. Most notable
in Samba 3.6 is the first free software implementation of Microsoft’s new
SMB2 file-serving protocol. The brand-new asynchronous server architecture
allows Samba’s new SMB2 server to double the performance of some network
applications when run with Microsoft Windows 7 clients. In addition, the print
subsystem has been rewritten completely to use automatically generated remote
procedure calls and provides greater compatibility with the Windows SPOOLSS
print subsystem architecture. Other features include improved clustered file
server support, simplified identity mapping and greater reliability, among others.
http://www.samba.org
WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 47
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NEW PRODUCTS
Steve Parker’s Shell Scripting:
Expert Recipes for Linux, Bash,
and More (Wrox)
A Linux geek’s reference shelf without a book on
shell scripting is painfully lonely. If your books are
experiencing this loneliness, consider picking up Steve
Parker’s new book Shell Scripting: Expert Recipes for
Linux, Bash, and More. This Wrox title is billed as
“a compendium of shell scripting recipes that can
immediately be used, adjusted and applied”. With this
book, Linux expert Steve Parker shares a collection
of shell scripting recipes that can be used “plug and
play” or easily modified for a variety of environments
or situations to avoid re-inventing the wheel. The book covers shell programming, with
a focus on Linux and the Bash shell; it provides credible, real-world relevance, as well as
including the flexible tools to get started immediately.
http://www.wrox.com
Lipson Robotics’ Robot Sculptures
All right geeks, let’s drop everything and talk Christmas presents!
Have you dropped any gift hints yet? Good, because good things
(sometimes) come to those who procrastinate. We suggest
requesting the gift of art, specifically art that a computer nerd can
love and appreciate. We recently stumbled upon the whimsical
robot sculptures from New York City artist David Lipson. Lipson
assembles these one-of-a-kind robots from random new and
old objects. All are inspired by Lipson’s love of tin toy robots,
sci-fi movies and retro design. Each artwork is sold exclusively at
Animazing Gallery in New York City, as well as via the gallery’s Web site.
http://www.lipsonrobotics.com and http://www.animazing.com
48 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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NEW PRODUCTS
BlackSky Computing’s Apollo
Enterprise HPC Storage System
It’s easy being green with BlackSky Computing’s Apollo Enterprise HPC Storage System, a
massively scalable storage architecture that packs 180TB in a 4U chassis while maintaining a light
footprint. Apollo can be expanded to support a single filesystem of more than 2 Petabytes “with
no degradation in performance”, says BlackSky, and it can work with HPC data sets up to 80Gb/s,
making the system reportedly “four times faster the I/O and one-fourth the price of the leading
competitors”. BlackSky built Apollo because all others failed its own internal needs, which include the
following requirements: tremendous capacity at low-price/TB, proportional network bandwidth in and
out of the device that will cripple HPC applications if not done correctly and expandability under
one filesystem to very large volumes. Other features include full redundancy and a Web-based UI.
http://www.blackskycomputing.com
Michael Sikorski and Andrew Honig’s
Practical Malware Analysis (No Starch)
Get smart and ward off malware by thoroughly understanding it
and those who make it by reading Practical Malware Analysis: The
Hands-On Guide to Dissecting Malicious Software. The new book,
authored by Michael Sikorski and Andrew Honig and published by No
Starch Press, provides a rapid introduction to the tools and methods
used to dissect malicious software, showing how to analyze, debug
and disassemble these threats safely. The book goes on to examine how to overcome the
evasive techniques—stealth, code obfuscation, anti-debugging, encryption, packing and
others—that malware authors employ to thwart analysis attempts. Key chapters include a
lab at the end, which reviews important concepts from the discussion in the context of
real-world malware examples. Both beginners and veterans alike will find the book useful.
http://www.nostarch.com
Please send information about releases of Linux-related products to [email protected] or
New Products c/o Linux Journal, PO Box 980985, Houston, TX 77098. Submissions are edited for length and content.
WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 49
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NEW PROJECTS
Fresh from the Labs
PdfMasher—E-Book Conversion
http://www.hardcoded.net/pdfmasher
If you’ve had problems reading PDF files
on various devices (like mobile phones),
PdfMasher may be just what you’re looking
for. According to the Web site:
PdfMasher is a tool to convert PDF
files containing text in ready-fore-book HTML files. Most e-book readers
support PDF files natively, but it’s often
a real pain to read those documents,
because we don’t have font-size
control over the document like we
have with native e-books. In many
cases, we have to use the zooming
feature, and it’s just a pain. Another
drawback of PDFs on e-book readers is
that annotations are not supported.
There are already tools to convert PDFs
to e-books, like Calibre, but what
they do is try to guess the role of each
piece of text in the PDF (and that’s if
you’re lucky). I think that in all but the
simplest cases, it’s a mistake to think
that anything short of an AI can do
that kind of guessing.
Installation If you can install this with a
binary, by all means do so. Available on the
site are 32- and 64-bit Linux .deb packages
for the ubiquitous Intel x86 architecture. For
masochists, or those who don’t have an Intelbased CPU, there is the obligatory source.
In order to grab the latest source, first
you need to install hg, which was under the
package name “mercurial” on my Kubuntu
system. Once that’s installed, grab the
Using PdfMasher, PDF files like these can be manipulated manually for conversion into other formats.
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latest source by entering the command:
n jobprogress 1.0.0
(http://hg.hardcoded.net/jobprogress)
$ hg clone https://bitbucket.org/hsoft/pdfmasher
n Sphinx 1.0.7 (http://sphinx.pocoo.org)
Once that has finished downloading,
keep this terminal open where it is,
because next you’ll need to sort out the
library requirements, and then you’ll
return to this terminal and continue
the installation. As far as dependencies
are concerned, the documentation lists
the following:
n Python 3.2 (http://www.python.org)
n pdfminer3k (http://hg.hardcoded.net/
pdfminer3k)
n pytest 2.0.3 to run unit tests
(http://pytest.org)
n Markdown 2.0.3
(http://www.freewisdom.org/
projects/python-markdown)
n PyQt 4.7.5
(http://www.riverbankcomputing.co.uk/
news)
With the dependencies out of the way,
With the original PDF on the left and outputted HTML on the right, this e-book now can be read on any
device without readability woes.
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re-open the terminal from before and enter
the following commands:
$ cd pdfmasher
$ python configure.py
$ python build.py
Then, run the program with:
$ python run.py
If you’re lucky enough to have the binary
installed, you simply can run the program with
the command:
$ pdfmasher
Usage Before I try to explain how to
use PdfMasher myself, I should include the
following from the Web site:
PdfMasher asks the user about the role
of each piece of text, and does it in an
efficient manner. Your PDF has a header
on each page, and you don’t want them
to litter your text? Sort text elements
by Y-position (thus grouping them all
together); Shift-select the elements
and flag them as ignored. They will not
appear on your final HTML. Your PDF
has footnotes on many pages? Sort your
elements by text content (thus grouping
all elements with the text starting with
a number together) and flag them as
footnotes. They will be moved to the end
of the document, and PdfMasher will try to
create hyperlinks to footnote references.
Before changing things under PdfMasher,
I recommend having your PDF open to one
side in another program so you can crosscheck bits of text as you’re culling sections.
When you’re ready to start, click on Open File
and choose the PDF you want to “mash”.
Once open, the pane below fills up in a
manner that at first glance is overwhelming
and incomprehensible. However, on a very
basic level, each line is a section of text
in your PDF. If you explore each line, you
can check which part of the PDF is being
examined, and if it’s redundant, you can
choose to ignore it in the conversion.
Looking at these PdfMasher lines in
detail, each line has an X and Y axis
reference, as well as font size, text length
and page number. Whenever you click a
line, the full text content of its section in
the PDF is shown in the pane below.
If you’ve decided on which sections to
remove, click Ignore to cut out the text
from the final product. Click Normal to
reinstate the text for inclusion. Depending
on which device you’ll be reading the
resulting e-book, the header and footer
information may be something you want to
cut out of the page.
For example, in the screenshot, I’m
removing the beginning references and
page headers in a psychology paper
that otherwise would leave a hard-tonavigate, garbled mess if I translated it into
something I could read on my phone.
However, if what you’re preparing is
intended to be something like a public
Web page instead of a trimmed-down
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e-book, you might want to use the Title
and Footnote buttons. Title will result in an
H1 title header in the outputted HTML. The
Footnote button will move the text to the
bottom of the document, and PdfMasher
will try to make one of the cool hyperlinks
mentioned earlier.
Once you’ve finished editing your
document, click on the Build tab below,
and then click on the Generate Markdown
button. A raw text file will be generated in
the same folder as the original PDF. Click on
Reveal Markdown, and the source folder will
be opened in your default file manager. Edit
Markdown will open the actual text file in
your default text editor, and View HTML will
show the end product in a Web browser.
If you’ve made any errors, the output will
reveal them quickly, and you can go back
and simply start the Build process again.
From here, you either can leave your output
as is or convert your files into specific
e-book formats.
Either way, PdfMasher uses some very
simple methods to create something very
clever and is a must-have for any regular
e-book reader.
Free Poker DB—Advanced On-line
Poker Database
http://fpdb.wiki.sourceforge.net
According to its Freshmeat entry:
Fpdb currently supports flop games
(Hold ’em, Omaha, Omaha hi/low),
stud games (7 card stud, Stud 8 and
Razz) and draw games (2–7 Lowball
single and triple draw, Badugi and 5
card draw).
Cash games are fully supported, and
tournament support is improving all
the time.
Currently supported sites include
PokerStars, Full Tilt Poker, the Everleaf
network, the Boss Media network
and others; see Features for a full list.
Additional poker sites can be supported
by writing a plugin to parse the site’s
hand history files. Several additional
plugins are under development and in
the development tree.
Installation Binaries may be available in
your repository (called python-fpdb on my
Kubuntu system). Source also is available,
and it doesn’t seem to require any awkward
compiling. To get an idea of the library
requirements, the documentation noted the
following successful package combination
for Ubuntu 9.10:
n Python 2.6
n GTK+ 2.18.3
Fpdb is a free/open-source tracker/
HUD for use with on-line poker. The
intent is to make fpdb capable of
supporting all games on all sites.
n PyGTK 2.16.0
n matplotlib 0.99.0
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n numpy 1.3.0
n sqlite3 2.4.1
n sqlite 3.6.16
n database mysql
Note the SQL dependencies, as they
are particularly important. The fpdb wiki’s
installation section has a very involved
section regarding MySQL under Gentoo,
so hopefully a combination of the
provided Ubuntu and Gentoo instructions
will point you in the right direction for
your system.
For those running with source, once you
have the library requirements out of the
way, you either can grab a source tarball or
set up a local repository with git. For the git
option, enter the command:
$ git clone git://git.assembla.com/free_poker_tools.git
For those wanting to use the source tarball,
grab the latest tarball from the Downloads
page and extract it. Open a terminal in the
new folder, and you should be able to run the
program simply by entering:
$ ./run_fpdb.py
Whereas my Kubuntu binary ran with the
command:
$ fpdb
Usage Before you start using fpdb, you
obviously have to play some poker on one
of the supported games, building up an
account with some dealt hands against
other players and whatnot. Once you’ve
done that, you need to locate the local
Fpdb provides impressive player statistics to give you the edge in on-line poker.
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NEW PROJECTS
account files for this game
so fpdb can find it later.
The best supported
commercial site for Linux
is PokerStars, as it runs
almost perfectly under
Wine. As a religious guy,
I can’t actually play for
money, but I can vouch
for PokerStars as it does
have a “Play Money”
mode for people like me.
However, the developers
did make it clear to me
that fpdb is focused on
real money games, so play
money support isn’t well
tested but should work for
Fpdb’s profit graph: looks like ChazDazzle had a bad weekend!
PokerStars’ cash games.
in the panel on the right.
Moving back to fpdb,
This last step really shows you how to
once you have some data ready to go,
use all of the other viewers as well, so feel
click on the Import menu and choose Bulk
free to explore the other features to your
Import. Browse for the file(s) of your poker
heart’s content—Ring Player Stats, Tourney
site below, and choose your game from the
Stats, Positional Stats, it’s all there. And
Site filter drop-down box. Now, click Bulk
don’t feel restricted to your own account
Import and wait a moment for your data to
either. You also can see the stats of other
be processed.
players, which, when you think of it, is
I can take you through only a few basic
really the whole point of this program!
steps, but it should be enough to get you
Ultimately, Free Poker DB will give a
started, after which you should pick up
genuine edge to any serious on-line poker
things pretty easily. Looking at the graphs
players, particularly those taking part
first, click on the Viewers menu and choose
in tournaments and the like. However,
Graphs. Find your game(s) below, and enter
I’d like to end this month on a slightly
your user ID. Now in the Sites pane, check/
different note—an unsolicited comment
uncheck the games you want to display,
from co-developer “Chaz” on some heartand choose Refresh Graph at the bottom. If
warming realities of OSS:
all went well, a profit graph should display
WWW.LINUXJOURNAL.COM / NOVEMBER 2011 / 55
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NEW PROJECTS
I got involved in the project about
a year ago after leaving my job
as a management consultant in
Washington, DC, to start Pokeit.
Pokeit is a similar product to fpdb,
except it’s a Web application and a
commercial venture. On the face of
it, Pokeit’s collaboration with fpdb
might seem a bit odd, given that we’re
trying to charge for something that
fpdb gives away for free. In practice,
it feels perfectly natural, and really it
should. It almost goes without saying
that you can’t launch a business
today without depending on opensource software—whether that be
databases, such as MySQL or Postgres,
free development tools, languages,
add-on modules or niche libraries.
Likewise for us, any tools that track
and analyze hands of Internet poker
require a set of core functionality for
reading and storing data. Developing
such a core function from scratch
would have been a monumental waste
of time for us when fpdb already
had a two-year head start and strong
foundation already built. So instead of
going it alone, we decided early on to
collaborate with fpdb on developing
the codebase in as many ways as it
made sense.
Let’s hope his example catches on.■
John Knight is a 27-year-old, drumming- and bass-obsessed
maniac, studying Psychology at Edith Cowan University in Western
Australia. He usually can be found playing a kick-drum far too much.
The Positional Stats are comprehensive to say the least.
BREWING SOMETHING FRESH, INNOVATIVE OR MIND-BENDING? Send e-mail to [email protected]
56 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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BUILDING AN
ULTRA-LOW-POWER
FILE SERVER WITH
THE TRIM-SLICE
HOW-TO: replace a large, inefficient
custom-built file server with the Trim-Slice.
DANIEL BARTHOLOMEW
F
or the past several years, I’ve used a custom-built
file server at my house. I’ve upgraded it many times,
but it began life, as near as I can recall, in April
2000. When I say “upgraded”, I mean the internals
have been swapped completely on at least two
occasions among other things. The most-recent major upgrade
was in 2006 (or thereabouts) when I added a software RAID5
with three 500GB hard drives (later expanded to six). It has
chugged along merrily for years, but lately it has begun showing
its age. For starters, two terabytes of space isn’t all that much
anymore. Also, it’s not as efficient power-wise as I would like
(in my measurements, it draws between 1.8 and 2.0 amps
continuously, depending on load). Finally, the case for this server
takes up way too much space (it’s a full tower).
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Figure 1. The Trim-Slice and Everything That
Comes in the Box
As an experiment, and finally to get rid
of that large, inefficient and ugly tower
case, I decided to use the new Trim-Slice as
the base for an ultra-low-power, ultra-small
replacement file server. The Trim-Slice is
built on the NVIDIA Tegra 2 platform, and
the specific model I purchased features a
1GHz dual-core ARM Cortex A9 processor,
1GB of RAM and a 32GB SATA SSD. Did I
mention that it’s really small? You know,
teeny—like, I-can’t-believe-this-is-afull-computer small. The dimensions are
130mm x 95mm x 15mm. For comparison
purposes, a standard 3.5" hard drive has
dimensions of approximately 146mm x
102mm x 25mm.
On the outside, it has an RS232 serial
port, SD and microSD card slots (both SDHCcompatible), four USB ports, HDMI and DVI-D
video out ports, 802.11n and a Gigabit
Ethernet port. Inside, it comes with Ubuntu
pre-installed on the SSD (10.10 “Maverick”
was installed on the one I received, but there
is now an update to 11.04 “Natty”, which I
applied and which I expect is now shipping on
newly ordered units).
The full Ubuntu Linux inside is what set
this solution above alternatives like the
Drobo FS, ReadyNAS and others, at least in
my mind. The price is in the same ballpark
too. The model I ordered, complete with
shipping from Israel, came to $335.
The main downside for my purposes is
that there is no place to connect internal
hard drives. I have to make do with external
USB drives instead. I don’t like the thought
of running a software RAID over USB, so I
further decided simply to use multiple large
external USB drives (each with at least one
corresponding backup drive).
To start with, my goal was to replace the
old tower server, which just requires the
Trim-Slice and two 2TB external USB hard
drives. Yes, a single hard drive, especially
a USB drive, is not as reliable or nearly as
fast as a RAID5 array, but it’s a compromise
Figure 2. Size Comparison: the Trim-Slice Next to
a Nokia N900 and the Ben NanoNote
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FEATURE Building an Ultra-Low-Power File Server with the Trim-Slice
I’m willing to make for the power, space
and noise savings. USB is plenty fast for
my needs, and besides, with two drives, I
have a backup.
Anatomy of a File Server
The purpose of a file server is to serve files
over a network. There are many ways to
do this, but I focus on the most common
ones here.
First, there is classic “file server”
software: NFS and Samba. These systems
don’t care what your data is. All they see
are files, and no file is any different from
the next (apart from size and permissions).
The new kids are content-aware file
servers like UPnP and DAAP. This type of
file server software does care about content
types, and it serves up metadata about your
files along with the files themselves. It will
refuse to serve files it doesn’t recognize
or support. But, it can do some tricks that
NFS and Samba can’t, like alter data on the
fly for clients who can’t read the original
data. So, they’re more fussy than classic file
server software, both to set up and run, but
they do have advantages.
UPnP and DAAP are designed specifically
for serving audio, video and image files.
DAAP is built-in, or available as a plugin,
for many popular audio jukebox apps,
such as Rythmbox, Amarok and Banshee,
but there also are standalone server
applications available. UPnP Media Server
support is built in to various consumer
devices, such as the PlayStation 3, Xbox
360 and various handheld and set-top
media players.
NFS
NFS is the classic Network File System, and
it is has been in use for decades on Linux
and UNIX. The Popcorn Hour media player
connected to my TV supports NFS, and I
don’t have any Windows computers, so
NFS is really the only classic file-serving
protocol I need (or want) on my network.
NFS has very limited security, so it’s not
ideal for everyone, but it’s lightweight and
easy to configure. In my opinion, if you
have a device that supports NFS and SMB,
go with NFS.
On Ubuntu, the NFS server I use is called
nfs-kernel-server, and you can install it with
the following:
sudo apt-get install nfs-kernel-server
To create an nfs share, edit the /etc/
exports file, and add the directory you want
to export. Here is an example:
/mnt/disk01 popcorn(ro,sync,root_squash,no_subtree_check)
The above line exports the /mnt/disk01
directory to my Popcorn Hour, with the
following flags:
n ro — read only: in other words, don’t
allow anything that could change the
filesystem. The Popcorn Hour has the
ability to delete items, but I don’t want
to let my kids delete things arbitrarily or
accidentally with the remote.
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n sync — reply to requests only after
the changes have been committed to
stable storage.
Or, I could add an entry like the following
to my /etc/fstab file:
trimslice:/mnt/trimslice/disk01
n root_squash — map requests from
uid/gid 0 to the anonymous uid/gid. This
makes things a little more secure.
n no_subtree_check — from the man
page: “This option disables subtree
checking, which has mild security
implications, but can improve reliability in
some circumstances.” See the man page
for more information (man exports).
With the line in place, I run the sudo
exportfs -ra command to refresh the
exports. Then on the Popcorn Hour, I can
mount the exported directory, and away I
go. There are several other options you can
use in the /etc/exports file. See the exports
man page for details.
The example entry above can’t be
mounted on any other host, but to permit
other hosts to do so, I either can change
popcorn to the IP address and netmask
of the network I want to share it with
(for example, 192.168.10.0/24 for every
host with an IP address starting with
192.168.10.), or I can add additional host
definitions to the end of the line.
With the exports file updated and
refreshed, I can mount the export with
something like this:
sudo mount -t nfs trimslice:/mnt/trimslice/disk01
➥/mnt/trimslice/disk01
➥nfs
defaults
/mnt/trimslice/disk01
0 0
and the NFS share always would be
mounted at boot time.
Samba SMB/CIFS
Samba, aka SMB/CIFS, is how you go
about sharing files with computers
running Windows. If I had a Windows
machine or two, using Samba would be
a given. I don’t, but I’ll go ahead and
describe the process here. For starters,
Samba is installed on the Trim-Slice with
the following:
sudo apt-get install samba
After installation, edit the /etc/samba/
smb.conf file to set up your shares (add
them to the end of the file). A read-only
share equivalent to the NFS one described
above is:
[disk01]
comment = trimslice disk01
path = /mnt/disk01
browsable = yes
guest ok = yes
read only = yes
Add the above to the end of the
smb.conf file, and the share will pop into
existence on the network. With Samba,
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FEATURE Building an Ultra-Low-Power File Server with the Trim-Slice
there is no need to restart the service or run
a command after editing the smb.conf file;
any changes are applied automatically as
soon as the file is saved.
It’s a good idea to uncomment the
security = user line in the smb.conf
file to add some security (and if you do
want security, you should set guest ok
in the above example to no). And, if you
have a proper Windows network, you
should change the workgroup name in
the smb.conf file to the actual name of
your Windows workgroup.
As with NFS, you can enter a lot more
settings in the smb.conf file to tweak
things just the way you want them. The
default file is filled with examples, and
the Samba documentation goes into even
greater detail.
DAAP
DAAP, in case you are interested, stands
for Digital Audio Access Protocol. An
older, but serviceable, standalone DAAP
server for Linux is mt-daapd, also known
as the Firefly Media Server. Unfortunately,
it is not under active development. Some
forks are in the works (which aren’t in
the Ubuntu repositories yet), so maybe
the situation will improve in the future.
To install it, do the following:
sudo apt-get install mt-daapd
After installing mt-daapd, set the
password for the admin account in the
/etc/mt-daapd.conf file. Technically, the
Figure 3. mt-daapd, aka the Firefly Media Server
password already is set, but it’s good
practice to change it. You can tweak other
settings in the file, but the GUI is easier.
After changing the password, restart
mt-daapd with:
sudo /etc/init.d/mt-daapd restart
Then, go to the Web interface to
configure it: http://trimslice:3689 (replace
“trimslice” in the URL with the correct IP
address or name).
The configuration page is simple and
self-explanatory. You can set the name,
change the admin password and set
a password for listening to the music
(in case you don’t want to share your
collection of classic Dr. Who music with
everyone on your network). You also
set which folder or folders contain your
music (multiple folders can be specified).
Finally, you can configure how often
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to have mt-daapd rescan your music
folder(s).
Once the changes are to your liking,
pressing the Save button saves the settings
to the /etc/mt-daapd.conf file. But, the GUI
is there so you might as well use it.
All should be well and good at this
point. Unfortunately, mt-daapd, as
packaged in the repository the Trim-Slice
uses, does not support FLAC files. If your
collection is mostly MP3 files, that won’t
be an issue. If it is an issue, your options
are to compile your own, live with the
limitation or find an alternative.
UPnP
For serving up video files to my PS3,
I use the MediaTomb UPnP media server.
Or at least, I would, if I didn’t have
the Popcorn Hour. MediaTomb, like
mt-daapd, is a nice piece of software
and works just fine for what it does, but
devices like the PS3 can be very picky
about what file types they will support.
On-the-fly transcoding (supported by
both mt-daapd and MediaTomb) can
eliminate some of these issues, especially
with audio files (for example, by
transcoding a FLAC file to WAV while it is
being transferred, so that iTunes can play
it). Transcoding isn’t practical for video
files though. It can be done, but the CPU
requirements are hefty to say the least,
especially when you start talking about
720p and larger video files.
Limitations aside, installing and
configuring MediaTomb is similar to
mt-daapd. First, enter the following:
sudo apt-get install mediatomb-daemon
After the install completes, edit the
/etc/mediatomb/config.xml file to enable
the graphical user interface (GUI) and
set the default user and password. To
do this, change enabled="no" in the
following lines to enabled="yes"
(both of them), and set the password to
something more secure:
<ui enabled="no" show-tooltips="yes">
<accounts enabled="no" session-timeout="30">
<account user="mediatomb" password="mediatomb"/>
The above lines should be near the top
of the file. Save the file, and restart the
server with:
sudo /etc/init.d/mediatomb stop
Figure 4. The Media Tomb File Browser
sudo /etc/init.d/mediatomb start
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FEATURE Building an Ultra-Low-Power File Server with the Trim-Slice
Once restarted, connect to
http://trimslice:49152/. Enter the user
name and password, and you will be
in the GUI. To add a folder, click the
Filesystem link, and browse to the folder
you want MediaTomb to index. With
the correct folder selected in the left
pane, click on the plus, or plus-with-acircle icon, to have MediaTomb scan the
contents of the folder. The plus-with-acircle icon adds the folder as an autoscan
folder, meaning it will rescan the folder
periodically looking for new files.
For PS3 support, a couple lines need to
be changed in the config.xml file; they
are commented and easy to find if you
search for “PS3”.
Backups
With this new file server, I lose the
protection of RAID, so backups are
more important. RAID, of course, does
not eliminate the need for backups;
it just makes the primary filesystem
more reliable. Because I already needed
backups with my old setup, I had a
backup system in place.
The “system” itself is a custom rsync
backup shell script. The backup drive
contains several directories: one named
current and then 14 others named 01,
02, 03 and so on, up to 14. The basic
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flow of the script is:
rm -rf '14'
mv '13' '14'
mv '12' '13'
...
mv '01' '02'
cp -al 'current' '01'
rsync drive-to-back-up to 'current'
The -al part of the copy command
above is important. It tells the command to
operate in archive mode, which preserves
attributes and copies directories
recursively, and to create hard links
instead of actually copying the files.
When rsync comes upon a changed file,
it will de-link the file before updating it,
so the combination of rsync and the cp
command gives me 14 days of backups
(assuming the script is run once a day).
The extra space required for these
backups is low, so I can use the same
size drive for the backups that I do for
the primary. Once a backup drive starts
nearing its limit, the primary drive likely
will be close to its limit too, and it will
be time to shop for an additional pair
of drives.
I’ve used variations of this script for
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FEATURE Building an Ultra-Low-Power File Server with the Trim-Slice
Lots of excellent backup programs are
available for Linux. The point is to make
backups, as many as necessary.
Conclusion
The Trim-Slice has worked out very well as
a file server. The built-in serial port lets me
operate it completely without a monitor,
and the hardware has so far been more
than adequate for my household’s modest
file-serving needs.
With dual 2TB external USB disk
drives (and more to come), the Trim-Slice
is even more energy-efficient than I
thought it would be. My consumer-grade
“Kill-a-Watt” power meter (which I admit
is probably not very accurate) shows
an average power draw of 0.28 amps,
which, completely accurate or not, is
much better than the 1.8 to 2.0 amps the
old server was pulling. The power draw
of the Trim-Slice by itself is an astounding
0.08 amps.
Power is just one benefit. I also like the
smaller footprint. Noise is much better
too. The old case needed several fans,
but the Trim-Slice is passively cooled.
There are fans in the external drive
enclosures, but they don’t come on very
often, and when they do, I don’t notice
them at all. The Trim-Slice does get a bit
hot to the touch, but I suppose that’s
what you get when you make the outer
casing a heat sink.
The jury is still out on how long this
new setup will last. I consider USB drives
to be less reliable, and although the
build quality of the Trim-Slice appears
high, it’s a new product with no history.
To mitigate this, I am going to be very
careful to make sure important stuff is
copied across all future drives. Despite
my worries, I must admit, I did replace a
few of the drives in my RAID5 over the
years, and I don’t imagine the difference
in reliability will be so great as to cause
any huge problems. ■
Daniel Bartholomew works for Monty Program
(http://montyprogram.com) as a technical writer and system
administrator. He lives with his wife and children in North Carolina
and often can be found hanging out in #maria on Freenode IRC
(he occasionally pokes his head into #linuxjournal too).
Resources
The Trim-Slice: http://trimslice.com
The Trim-Slice User Manual:
http://trimslice.com/download/
documentation/trim-slice-user-guide.pdf
Linux NFS-HOWTO:
http://nfs.sourceforge.net/nfs-howto
Samba: http://www.samba.org
MediaTomb: http://mediatomb.cc
Firefly Media Server: http://en.wikipedia.org/
wiki/Firefly_Media_Server
The Popcorn Hour:
http://www.popcornhour.com
66 / NOVEMBER 2011 / WWW.LINUXJOURNAL.COM
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Nov. 16–18;
MiniConfs Nov. 14–15
For developers.
By developers.
8 th annual Open Source Developers’ Conference
this year at the Australian National University,
Canberra, Australia.
43
Speakers
6
MiniConfs
5
Days
with keynotes by Sen. Kate Lundy, Damian Conway,
Brian Catto, and Tony Beal.
schedule & registration at
osdc.com.au
LJ211-November2011.indd 67
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Learning
to Program
the Arduino
Want to learn how to program a microcontroller and
set up a home automation system? Read on to learn
the basics of Arduino so you can get started.
Amit Saha
T
his article should acquaint you with basic Arduino programming and show you how to
write programs that interact with objects in the real world. (A mandatory disclaimer: the
last time I really studied electronics was way back in high school, so this article focuses
more on the programming aspects, rather than the electronic side of things.)
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Physical Computing
Before I start talking about this really cool
thing called Arduino (Italian for “good
friend”), let me say a few things about the
fascinating subject of physical computing.
Physical computing has been defined in
various ways, but the central idea seems to
be the same: physical computing is concerned
with developing software that interacts with
the world beyond the host computer through
a combination of hardware and software—
it’s aware of the world, so to speak. Such
awareness makes these applications capable
of sensing external events and responding
to them in a predefined way. This is
accomplished by the use of sensors and
actuators (which I describe next).
Actuators and Sensors
The Arduino interacts with the world through
actuators and sensors. Sensors are electronic
components that describe the world to your
application. One common way sensors work
is that their electrical properties change (in a
mathematically known way) as an effect of
the changes in the conditions in which it’s
operating. For example, the resistance of a
photo-resistor changes when the intensity
of light incident on it changes. Thermistors
are another example of such sensors whose
resistance changes when the operating
temperature changes. A flex sensor is a
different category of sensor, where the
resistance changes depending on the extent
of the flex or “bend”. Such changes can be
read as electrical signals on the Arduino’s
input pin. Depending on the kind of sensor,
the signal either can be digital (on or off) or
analog (a continuous stream of values). The
latter part of this article shows how to work
with analog sensors.
Actuators, on the other hand, are electronic
components that are used to react to an
external event. For example, when it gets
dark, the light should be switched on.
Sensors and actuators, thus, are used to
achieve complementary objectives: one
senses, and the other reacts. Examples of
actuators are solenoids and servos. Later
in this article, I explain how to control a
servo using Arduino.
Arduino
The Arduino is an open-source electronics
prototyping platform composed of two major
parts: the Arduino board (hardware) and the
Arduino IDE (software). The Arduino IDE is
used to write the program that will interact
with your Arduino and the devices connected
to it. In the Arduino world, such a program
is called a sketch, which has its origin in its
mother language, Processing (see Resources).
The Arduino board is a small-form
microcontroller circuit board. At the time of
this writing, a number of Arduino boards
exist: Arduino UNO, Nano, Mega, Mini, Pro
and others (see Resources for a complete
list). The Arduino UNO (Figure 1) is the
latest version of the basic Arduino board,
and you need one of these to follow this
article (see Resources for the UNO’s detailed
specifications).
Besides the UNO, you need the following
hardware to work through this article:
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FEATURE Learning to Program the Arduino
Figure 1. Arduino UNO
(Courtesy of http://arduino.cc/en/Main/ArduinoBoardUno)
1. Breadboard to set up the circuit.
2. Some LEDs.
3. Resistors: 330 Ohm (at least as many as
LEDs), 10 kOhm resistors.
4. Continuous rotation servo (SpringRC
SM-S4303R continuous rotation servo:
http://www.robotgear.com.au/
Product.aspx/Details/482).
If you haven’t already opened up your
Arduino and plugged it in to your USB
port, plug it in. For the purposes of this
article, it will be sufficient to use the
power supply via the USB connection. If
you connect more devices, you will need
to connect an external supply.
You will program the Arduino in a
language that looks very similar to C
and is based on Processing. You can
download the Arduino IDE from the
Arduino Project Web site.
Arduino IDE
As you might guess, the IDE is as always
the front end. The real pieces are the
compilers, linkers and libraries that need to
be present to communicate and program
the AVR microcontroller-based Arduino.
Depending on your Linux distribution, the
exact names of the packages will vary, so
I just list the software by name here:
n The GNU C and C++ compiler for AVR.
n AVR binutils.
5. Flex sensor.
n AVR libc.
6. Linear potentiometer.
7. Connecting wires.
One excellent way to get started with
Arduino is the Arduino starter kit from
Sparkfun. This starter kit contains all the
hardware and more that you need to follow
this article (except the servo).
n avrdude (a program for uploading code to
the microcontroller board).
n rxtx (for serial communication).
Once these packages are installed, fire
up your Arduino IDE. Take a moment to
explore the IDE. The buttons for compiling
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(verifying) and uploading the sketch are the
important ones.
The communication between your
computer and the Arduino will be via
the USB cable that has been packaged
with your Arduino board. Once you plug
the USB cable in to your computer (with
the other end plugged in to the Arduino
board), it should show up in the Arduino
IDE under Tools→Serial Port as /dev/
ttyACMx. If you have more than one USB
serial device communicated, be careful to
select the correct one. You need to set up
user permissions correctly to access the
serial port (see Resources for distributionspecific instructions).
Blink Those LEDs
For the first sketch, let’s blink an LED and then
extend it to blink multiple LEDs alternately.
Before the software part, let’s first set up the
circuit to connect the LED to the Arduino. The
Figure 2. Circuit for a Single LED Blink
Listing 1. Simple LED Blink Sketch
/*
Blink
Turns on an LED on for one second,
then off for one second, repeatedly.
This example code is in the public domain.
*/
void setup() {
// initialize the digital pin as an output.
// Pin 13 has an LED connected on most Arduino boards:
pinMode(13, OUTPUT);
}
void loop() {
digitalWrite(13, HIGH);
delay(1000);
digitalWrite(13, LOW);
delay(1000);
}
//
//
//
//
set the LED on
wait for a second
set the LED off
wait for a second
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FEATURE Learning to Program the Arduino
completed circuit should look like Figure 2.
Next, in your Arduino IDE, open the
sketch in Examples→Basics→Blink, which
should look like Listing 1.
As you can see from that sketch and
the circuit diagram, the LED is connected
to the digital pin 13 of the Arduino.
Once you verify (compile) the sketch
and upload it to the Arduino board, you
should see the blinking LED.
Because this is your first sketch, take some
time to understand the general framework
of an Arduino sketch. If you are familiar with
C or C++, you will notice that you have two
functions in this sketch: setup() and loop().
The code that you write in setup() is meant for
initialization and is executed once the sketch
is uploaded to the board. The code in loop() is
executed repeatedly as long as the power to
the Arduino is supplied. Even if you power off
Listing 2. Multiple LED Blink Sketch
/* Multiple LED Blinking program
Amit Saha
*/
// constants won't change. Used here to
// set pin numbers:
const int numPins = 3;
const int ledPin [] =
{11,12,13};
// the number of LED pins
int interval = 100;
// interval at which to blink (milliseconds)
void setup() {
// Iterate over each of the pins and set them as output
for(int i=0;i<numPins;i++)
pinMode(ledPin[i], OUTPUT);
}
/* Loop until death */
void loop()
{
for(int i=0;i<numPins;i++)
{
digitalWrite(ledPin[i],HIGH);
delay(interval);
digitalWrite(ledPin[i],LOW);
delay(interval);
}
}
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the Arduino and power it back on, the sketch
still resides until you overwrite it with another
sketch. An Arduino sketch should be saved in
a file with the extension pde and is stored in a
directory of the same name.
For the next sketch, let’s connect multiple
LEDs and blink them alternately to create
a cool rippling effect. (You might want to
Listing 3. Fade an LED On/Off Using a Linear Potentiometer
/* Using potentiometer to fade on/off an LED
*
Original code notice below:
* -----------------------------* Demonstrates analog input by reading an analog sensor on
* analog pin 0 and turning on and off a light emitting
* diode (LED) connected to digital pin 13.
* The amount of time the LED will be on and off
* depends on the value obtained by analogREAD().
* Created by David Cuartielles
* Modified 16 Jun 2009
* By Tom Igoe
* http://arduino.cc/en/Tutorial/AnalogInput
*/
int sensorPin = 0;
int ledPin = 13;
int sensorValue = 0;
void setup() {
//declare the ledPin as an OUTPUT:
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
}
void loop() {
sensorValue = analogRead(sensorPin);//
digitalWrite(ledPin, HIGH);
delay(sensorValue);
digitalWrite(ledPin, LOW);
delay(sensorValue);
}
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FEATURE Learning to Program the Arduino
Listing 4. Fade an LED On/Off Using a Flex Sensor
/* Flex sensor + LED
/* Analog Input
* Demonstrates analog input by reading an analog sensor
* on analog pin 0 and turning on and off a light emitting
* diode (LED) connected to digital pin 13.
* The amount of time the LED will be on and off depends
* on the value obtained by analogREAD().
* Created by David Cuartielles
* Modified 16 Jun 2009
* By Tom Igoe
* http://arduino.cc/en/Tutorial/AnalogInput
* Modified 16 July, 2011
* By Amit Saha
* Current code was tested with a Flex sensor
*/
int sensorPin = 0; /*Flex sensor pin */
int ledPin = 13; /* LED pin*/
void setup() {
pinMode(ledPin, OUTPUT);
}
void loop() {
int loop=1;
float sensorValues=0.0,delaytime;
for(loop=1;loop <=10 ;loop++)
{
sensorValues = sensorValues + analogRead(sensorPin);
}
//Use the average as a delay value
delaytime = sensorValues/10;
digitalWrite(ledPin, HIGH);
delay(delaytime);
digitalWrite(ledPin, LOW);
delay(delaytime);
}
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Figure 3. Circuit for Multiple Blinking LEDs
connect more than three LEDs of different
colors.) The circuit for this sketch is shown
in Figure 3.
Once you have uploaded this sketch to
your Arduino UNO board, your LEDs should
put on a colorful performance.
flex sensor in place of the potentiometer
of the earlier circuit. A flex sensor is an
analog sensor whose resistance changes
with its bending angle. You will see that
the resistance changes as you bend on
either side—increasing on one side and
decreasing on the other. The Arduino
sketch is shown in Listing 4.
The flex sensor has two pins: one end
should be connected to the +5V input, and
the other pin should be connected to the
analog pin 0 and farther on to the ground
via a 10 kOhm resistor.
Listing 5. Example of a Server Sketch
/* Serial communication demo: +1*/
/* Server program
Analog Sensors
In the first sketch, you turned the LED
on and off by writing to the Arduino’s
digital pin. What if you wanted
something in between—say, to fade on
and off? Say hello to a tiny little device
called a potentiometer. To set up the
circuit, connect the central pin of the
potentiometer to the analog pin 0, and
the other two pins to the +5V supply and
ground, respectively. The LED should be
connected as in the first sketch.
In Listing 3, you can see that the reading
from the potentiometer is used to control
the delay time, so the effect of fading in
and out is produced.
Next, let’s use an electronic component
called a flex sensor to (you guessed it)
control an LED. Basically, let’s use the
Amit Saha*/
int number;
void setup()
{
// Open the serial connection, 9600 baud
Serial.begin(9600);
}
void loop()
{
// Get the data "packet"
// Wait for some data to arrive
if (Serial.available()>1) {
//operation=Serial.read();
number=Serial.read();
Serial.println(number + 1);
}
}
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FEATURE Learning to Program the Arduino
Serial Communication
All the sketches so far have made use of
the Arduino library calls to read and write
to the Arduino pins. You haven’t directly
made use of the serial communication
between the host computer and the
Arduino board. First, I’ll describe how to
write a basic client/server style program.
The “server” program is a sketch that
lives on the Arduino board waiting for serial
data to be available (an integer in this case)
and sends back the number by adding 1 to
it to the “client”.
The client side of the program is
written in Processing using its serial
library (Listing 6).
To run the client, download the
processing IDE and create a new sketch
with the code as shown in Listing 5. Run
this code after you have uploaded the
server sketch (Listing 5) to the Arduino.
Controlling a Servo
Now, let’s make things move with your
Arduino code. For this example, let’s
control the movement of a servo—that
is, start and stop the servo and control its
speed and rotation. Three wires protrude
out of the servo: control (white/yellow),
power (red) and ground (black/brown).
First, set up the circuit such that the the
control wire is connected to the Arduino’s
digital pin 2, the red wire is connected
to the Arduino’s 5V input and the black
wire to the ground. Now, upload the
sketch (Listing 7) to your Arduino. You
also optionally may connect an LED to
the digital pin 13 (in the same way you
connected a single LED earlier), which
will turn on or off depending on whether
the servo is rotating.
Once the sketch is uploaded, open
a serial communication channel using
screen (feel free to substitute it with your
favorite terminal communication program).
Type screen /dev/tttyACM0 9600,
and you should see the “servo prompt” at
your service:
Arduino Serial Servo Control
Keys:'(s)lower' or '(f)aster', spacebar to center and o to stop
Pressing the keys to the servo should
produce the desired behavior. If you see
the code listing for the servo mechanism,
you will see that the key to controlling the
speed is basically the duration of the delay
(variable pulseWidth) between sending a
HIGH and LOW signal to the servo. Here,
we are simulating an analog behavior
using the important technique called Pulse
Width Modulation, which you can read
about elsewhere.
If you have gotten this servo example
up and running, you also might want to
check out the other example sketches for
working with servos in the Arduino IDE
under File→Examples→Servo.
A Peek under the Hood
I’m drawing toward the close of this
article, and I hope you have had a lot
of fun. However, if you are like me, you
already have started wondering what’s
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Listing 6. Example of a Serial Client Sketch
/*Client for Serial communication*/
/* Amit Saha */
import processing.serial.*;
Serial myPort; // The serial port
// initial variables:
int i = 1; // counter
char inData;
void setup () {
size(400, 350); // window size
// List all the available serial ports
println(Serial.list());
// Pick up the first port, since I usually have
// just the Arduino connected.
// Make sure the correct port is selected here.
myPort = new Serial(this, Serial.list()[0], 9600);
myPort.clear();
// set initial background:
background(255); }
void draw () {
myPort.write(4);
//myPort.write(5);
if (myPort.available() > 0) {
inData = (char)myPort.read(); // Typecast it to the corresponding
// character for the
// ASCII value
serialEvent();
}
}
void serialEvent () {
System.out.println(inData);
}
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FEATURE Learning to Program the Arduino
Listing 7. Servo Control Sketch
/*
* servo1: servo1.pde
* Servo control from the Serial port
*
* Slower, faster, Center and Stop a Servo with an LED Blinky
* Created: 1 June, 2011, Amit Saha (http://echorand.me)
* Adapted from http://principialabs.com/arduino-serial-servo-control/
*/
/**
int
int
int
int
Adjust these
servoPin
minPulse
maxPulse
turnRate
int refreshTime
values for your servo and setup, if necessary **/
= 2;
// control pin for servo motor
= 500; // minimum servo position
= 3000; // maximum servo position
= 10; // servo turn rate increment (larger value,
faster rate)
= 20;
// time (ms) between pulses (50Hz)
int OFF=0; // This variable will be used to get/set the status of the servo
/** The Arduino will calculate these values for you **/
int centerServo;
// center servo position
int pulseWidth;
// servo pulse width
int moveServo;
// raw user input
long lastPulse
= 0;
// recorded time (ms) of the last pulse
/* LED setup*/
int ledPin=13;
void setup() {
pinMode(ledPin, OUTPUT); // LED Blink
pinMode(servoPin, OUTPUT); // Set servo pin as an output pin
centerServo = maxPulse - ((maxPulse - minPulse)/2);
pulseWidth = 0;
Serial.begin(9600);
Serial.println("
Arduino Serial Servo Control");
Serial.println("Keys:'(s)lower' or '(f)aster', spacebar to center
and o to stop");
Serial.println();
moveServo = 60;
}
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void loop() {
// wait for serial input
if (Serial.available() > 0) {
// read the incoming byte:
moveServo = Serial.read();
// ASCII 's' is 115, ASCII 'f' is 102, 'o' is 111, 'spacebar' is 32
if (moveServo == 115) { pulseWidth = pulseWidth - turnRate; OFF=0;}
//slower
if (moveServo == 102) { pulseWidth = pulseWidth + turnRate;OFF=0; }
//faster
if (moveServo == 32) { pulseWidth = centerServo; OFF=0;} //center
if (moveServo == 111) { OFF= 1;} //STOP
// limit the servo pulse at min and max
if (pulseWidth > maxPulse) { pulseWidth = maxPulse; }
if (pulseWidth < minPulse) { pulseWidth = minPulse; }
}
// pulse the servo every 20 ms (refreshTime) with current pulseWidth
// this will hold the servo's position if unchanged, or move it if
// changed
if (OFF == 0)
{
/* Turn ON the LED*/
digitalWrite(ledPin,HIGH);
if (millis() - lastPulse >= refreshTime) {
digitalWrite(servoPin, HIGH);
// start the pulse
delayMicroseconds(pulseWidth); // pulse width
digitalWrite(servoPin, LOW);
// stop the pulse
lastPulse = millis();
// save the time of the last pulse
}
}
else
{
/* Turn OFF the LED*/
digitalWrite(ledPin,LOW);
//Stop the servo
digitalWrite(servoPin, LOW);
}
}
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FEATURE Learning to Program the Arduino
going on behind the scenes—the journey
of the processing sketch to the bytes
getting executed on the Arduino board.
The real work behind the scenes is
done by the GNU C/C++ compilers,
linkers and libraries for the AVR
microcontroller. If you hold the Shift key
when you compile your sketch, you will
see that the commands - avr-g++,
avr-g++, avr-ar and avr-objcopy
are invoked. First, your Arduino sketch
is converted to a suitable C++ file
(with the .cpp extension), which then is
compiled, linked and finally converted
to the hex file that is uploaded to the
Arduino board. You can see all these
intermediate files in the /tmp/build*.
tmp directory. Knowledge of this build
process can enable you to bypass the
IDE for your Arduino development by
writing an appropriate Makefile. See the
“Command-line Arduino development”
article listed in Resources for an example.
Arduino ecosystem. Be sure to see the
Resources for this article for some of the
most interesting Arduino books, articles
and projects.
Also note that wires are good, but
only when you want to limit yourself to
the confines of your tabletop or even
your room. If you want your Arduino to
be out there, decoupled from your host
machine, you need to explore ways of
wireless communication. Say hello to XBee
modules, which allow communication
with the ZigBee communication standard.
And before I end, you might face
issues with erratic serial communication.
Especially during extended periods of
experimenting with serial communication,
I found that the serial ports would remain
locked or just be plainly not accessible
from the host computer. My advice is
to be patient. Unplug and plug back in
a few times, and try killing the lock file
manually. Now, you should be good to go.
Conclusion
I’ve described a few simple but cool things
that can be done with an Arduino, but
this article barely scratches the surface. A
number of excellent books are available
that list a great number of Arduino
projects you can build for fun and profit.
These are, of course, in addition to all
the excellent on-line resources available.
During exploring Arduino purely from the
various blog posts on the Web and a trialand-error-based approach to learning,
I discovered many great projects in the
Acknowledgements
Thanks to the awesome Arduino community
members for their documentation and
numerous other bloggers on the Web.
The Arduino circuit diagrams were drawn
with Fritzing (http://fritzing.org). ■
Amit Saha is currently a PhD research student in the area of
Evolutionary Algorithms and Optimization. Like his random echoes
show (http://echorand.me), he has been writing on myriad Linux and
open-source technologies during the past five years. Overall, he
loves playing around with a bit of this and a bit of that. He welcomes
comments on this article and beyond at [email protected]
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Resources
Author’s Code for This Article:
https://bitbucket.org/amitksaha/articles_code/src/6bed469945fd/arduino_article
Plumbing for the Arduino: http://www.concurrency.cc/book
PureData (Audio Processing and Visualization): http://puredata.info
Firefly Experiments (bridging the gap between Grasshopper, the Arduino microcontroller, the Internet and
beyond): http://www.fireflyexperiments.com
Arduino: http://arduino.cc
Processing Language: http://processing.org
Arduino Hardware (I/O Boards): http://www.arduino.cc/en/Main/Hardware
Arduino Uno: http://arduino.cc/en/Main/ArduinoBoardUno
Sparkfun’s Starter Kit for the Arduino: http://www.sparkfun.com/products/10174
Installing Arduino on Linux (for different distributions): http://www.arduino.cc/playground/Learning/Linux
Command-Line Arduino Development: http://shallowsky.com/software/arduino/arduino-cmdline.html
Getting Started with Arduino by Massimo Banzi, O’Reilly Media/Make: http://shop.oreilly.com/
product/9780596155520.do
Programming Interactivity: A Designer’s Guide to Processing, Arduino, and openFrameworks by Joshua
Noble, O’Reilly: http://shop.oreilly.com/product/9780596154158.do
Arduino Cookbook by Michael Margolis, O’Reilly: http://shop.oreilly.com/product/0636920022244.do
Arduino Language Reference: http://www.arduino.cc/en/Reference/HomePage
Tom Igoe’s Physical Computing Page: http://www.tigoe.net/pcomp
Experimenter’s Guide for Arduino: http://ardx.org/src/guide/2/ARDX-EG-ADAF-WEB.pdf
Arduino Tutorials (tronixstuff): http://tronixstuff.wordpress.com
Principia Labs, Arduino Serial Servo Control: http://principialabs.com/arduino-serial-servo-control
Make’s Arduino Web Site: http://blog.makezine.com/arduino
Arduino Tutorial on Lady Ada: http://www.ladyada.net/learn/arduino
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ROAMING
MEDIA
PORTABLE MUSIC DOESN’T NEED TO BE RESTRICTED
TO HEADPHONES. HERE’S A STEP-BY-STEP HOW-TO
ON SETTING UP A MUSIC SYSTEM THAT FOLLOWS
YOU AROUND THE HOUSE LIKE A PUPPY.
Michael Nugent
L
ike many of you, I store all my music digitally on a central server in my home.
The problem is when I walk from room to room, my music doesn’t come with
me. I could carry around an iThingy or put it on my phone, but I’d rather not have
to wear headphones, and no matter how awesome they are in their class, tiny phone
speakers still are tiny phone speakers. Fortunately, I have a lot of computer hardware lying
around from past upgrades, so it was fairly easy for me to come up with some small, older
systems for each area of my house. Now, instead of listening to music on a little device,
I use a device to tag my location and have the music follow me wherever I go.
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The system is easy to build and uses
mostly off-the-shelf open-source programs.
In addition to the player and control
system, you need a way of tagging your
location in the house. I use the Bluetooth
radio on my phone, but you also could use
RFID tags, Webcams with motion detection
or facial recognition, or pretty much
anything else that will let the system know
where you are. For this setup though, I’m
assuming you’re using a Bluetooth device.
The central piece to this project is a
server-based music player. I am using the
Music Player Dæmon (MPD), a wonderful
outside boxes may have trouble connecting
to it.
The audio_output section defines
where the music goes when it plays. In
this case, you want to transcode it to Ogg
format and send it to the Icecast server
on the same host (although you could
run these on different systems if it makes
sense for your setup). Within this section,
the port and password must match the
configuration for the Icecast server, and
the mount will define the portion of the
URI after the server name. For simplicity,
I’ve left it at /. If you start MPD after
THE SYSTEM IS EASY TO BUILD AND USES MOSTLY
OFF-THE-SHELF OPEN-SOURCE PROGRAMS.
server-based system released under the GNU
General Public License and available from
the repositories of most Linux distributions.
Install the software with your favorite
package management system. In addition to
this player, you need to set up a streaming
system. Icecast fulfills this requirement and
also is widely available. Install it as well.
Configuring MPD is fairly straightforward.
The default file for your distribution is
probably very similar to the example below,
but you may need to change a few things.
The music_directory entry should point
to the directory that contains the music
files and one bind_to_address should
contain the non-loopback name or address
of the server. If it binds only to 127.0.0.1,
this configuration file is set up, it will be
missing the Icecast socket to play to, so you
need to set that up next. I’ve added some
comments to the configuration below to
help document the options there:
music_directory
"/data/arown/files/audio" #Point this at
the top level of your music directory. If you have more than
one, a directory of symbolic links may help you.
playlist_directory "/var/lib/mpd/playlists" #The following
files must be writable. I suggest making the directory owned
by the user running MPD.
db_file
"/var/lib/mpd/database"
log_file
"/var/lib/mpd/log"
state_file
"/var/lib/mpd/state"
user
"mpd" #This is the user that the MPD
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FEATURE Roaming Media
program runs under. I highly suggest making this a nonroot user.
and 2 is the number of audio channels. Experimenting here
bind_to_address
may give you better or worse quality, depending on your audio
"templar" #Place your machine name here, not
"localhost" or "127.0.0.1" if you want to reach the MPD
hardware and number of speakers.
server from another machine.
}
filesystem_charset "UTF-8"
bind_to_address
"/var/lib/mpd/socket"
port
"6600" #This is the client control port for
starting and stopping the MPD player as well as building
playlists and changing server side volume.
log_level
"verbose"
input {
plugin "curl"
}
In order to finish off the server portion,
you need to configure Icecast to stream the
music it receives from MPD. The sample
Icecast configuration file is quite long, but
I’ve cut out the areas that I’ve changed.
Make sure that the source-password here
matches the password from the MPD server.
This allows the MPD server authorization to
stream music to Icecast:
audio_output {
type
"shout"
encoding
"ogg" #This is the media type for the stream,
<authentication>
<!-- Sources log in with username 'source' -->
if your player wants MP3, use encoding "mp3" and be sure you
<!-- This password must match the MPD password above -->
have the proper tools to transcode to MP3 on your box.
<source-password>passthis</source-password>
name
"MusicPuppy"
<!-- Relays log in username 'relay' -->
host
"localhost" #The name of the box
<relay-password>passthis</relay-password>
that the Icecast server is hosted on.
port
"8000" #The port of the
<admin-user>admin</admin-user>
Icecast server.
mount
<!-- Admin logs in with the username given below -->
"/" #This is the part
of the URI after the hostname. I have left it to "/" for
<admin-password>passthis</admin-password>
</authentication>
simplicity, but often things like "/music.ogg" are used
to make it clearer to the user.
password
"passthis" #The source password to the
Icecast server. You probably should change this to something
complex because you'll never have to type it in.
bitrate
"128" #The bitrate to transcode to. You
Be sure that the bind addresses and
ports are correct. The bind address can be
localhost if the MPD server is on the same
box. The port must match the port from
the MPD configuration above:
may want to raise or lower this based on your CPU, bandwidth
or your quality preference.
format
"44100:24:2" #This is three variables:
44,100 represents the sample frequency, 24 is the bitwidth,
<listen-socket>
<port>8000</port>
<bind-address>127.0.0.1</bind-address>
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</listen-socket>
While you’re in this configuration file,
change the default passwords from
“hackme” and “hackmemore” to
something more secure, and check the
location of the logs for debugging. Mine
are in /var/log/icecast, but yours may vary.
After you start Icecast, the server
configuration should be complete. At
this point, start MPD as well. It should
hook itself up to the Icecast port, and
the logs should be free of errors. Next,
an MPD client is needed in order to set
up playlists on the server. I use MPDroid
for this, an Android variant I use to
control playlists from my phone, but
there are clients for a wide variety of
platforms available via your package
manager or from http://mpd.wikia.com/
wiki/Clients. Fire up a client, and add a
few songs to a playlist for a test and tell
it to play. The Icecast access log (not the
MPD logs) should show that a SOURCE
has connected, and it should show a 200
return. For example:
that the connection between MPD and
Icecast is up and working properly, though
it does not tell you that any data actually is
being passed. For that, you’ll need to test it
end to end.
To test it, you need a music player that
supports Ogg format (or MP3 if you’ve
gone that route). I’ve chosen Rhythmbox
for this example, because it supports
Ogg, is popular across a wide range of
distributions and has a command-line
control system that you can use to start
and stop the music as well as set the server
URI. Install and launch Rhythmbox (or fire
up your favorite player with these features)
and set it to play from the Icecast URI. For
example, mine is at http://templar:8000/.
If you have changed the mount directive in
the MPD configuration file to "/music.ogg",
the URI would then be http://templar:8000/
music.ogg. Either way, when the music
player is pointed at this URI, the Icecast
access.log file should show something
like this:
mj-12 - - [01/Aug/2011:15:28:52 -0700] "GET /
➥HTTP/1.1" 200 1194382 "-" "-" 70
127.0.0.1 - - [20/Jul/2011:01:15:03 -0700] "SOURCE /
➥HTTP/1.0" 200 19 "-" "MPD" 424
This shows the incoming connection
from MPD on the local box, the current
date and time and the fact that this is a
SOURCE request as opposed to a player
request. It shows the directory accessed
“/”, the protocol used and the return code
“200”. This is a great source of verification
The format for this line is very similar
to the one above. The only real difference
is that this is a GET request instead of a
SOURCE request. Seeing this line in the
access logs without a corresponding error
in the error log shows you that the media
player is requesting the music stream from
the Icecast server properly.
If you don’t hear music at this time, go
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FEATURE Roaming Media
back over the setup and check the log files.
Check the volume level within MPD, and
make sure that the MPD client says a song
is playing. Many MPD clients also let you
stream music directly, so you can verify that
it’s working as well.
The next step is to set up your Bluetooth
token. In my case, this is my Android
phone, but pretty much any Bluetooth
device will work. Ranges vary, so placement
of the Bluetooth receivers is important to
avoid overlap or gaps in the area you’re
trying to cover.
The Linux package for Bluetooth support
is called Bluez. It is widely available and
comes as part of most distributions. Install
command line:
[email protected]:~$ hcitool scan
Scanning ...
D4:E9:C0:37:00:0Deris
Make a note of the Bluetooth ID, and
be sure that the name field is not blank. It
can be anything, but it has to be something.
After this step, you can turn off the
discoverable mode on the Bluetooth device
for increased security. You now have all the
information that you need.
The following script checks whether the
Bluetooth device is in range and stops or
starts the music player based on the result.
THE FOLLOWING SCRIPT CHECKS WHETHER THE
BLUETOOTH DEVICE IS IN RANGE AND STOPS OR
STARTS THE MUSIC PLAYER BASED ON THE RESULT.
this package if it is not installed on your
system already. You don’t need to make
any configuration changes, because all you
need to do is identify that the Bluetooth
device is in range. You don’t need to pair
with it or transfer data between devices.
After installing the Bluez package, start
the software. Your logs should show that
the software started correctly and that it
identified your Bluetooth hardware properly.
In order to find the Bluetooth token,
it needs to be put into discoverable
mode temporarily. Turn that on, and run
the following scan command from the
Replace the SERVER_URI variable with your
MPD/Icecast server and the BTADDR variable
with your device’s Bluetooth ID (this ID comes
from the hcitool scan command above):
#!/bin/bash
SERVER_URI="http://templar:8000/"
BTADDR="D4:E9:C0:37:00:0D"
DBUSADDR=`grep -z DBUS_SESSION_BUS_ADDRESS /proc/*/environ 2>
➥/dev/null|
sed 's/DBUS/\nDBUS/g' | tail -n 1`
if [ "x$DBUSADDR" != "x" ]; then
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export $DBUSADDR
else
echo "Cannot find DBUS Session for Rhythmbox. Please
be sure the application is running"
exit 1
fi
NAME=`hcitool name $BTADDR`
if [ -z "$NAME" ] ; then
`rhythmbox-client --pause`
else
`rhythmbox-client --play-uri=$SERVER_URI`
fi
Save this script as /usr/local/bin/
musiccontrol.sh. Next, add the script as a
crontab entry that runs every minute. This
entry must be run as the same user as the
user that owns the Rhythmbox process.
Edit the crontab from the correct user:
[email protected]:~$ crontab -e
Add the following line, and then save
and exit:
* * * * * /usr/local/bin/musiccontrol.sh
Now, turn on the Bluetooth device (it
does not need to be discoverable this time
because you already have the address). At
the turn of the next minute, the cron script
will see the Bluetooth device and then tell
Rhythmbox to start playing the music from
the MPD/Icecast server. If you move the
Bluetooth device out of range, the cron
script will no longer see the Bluetooth
device and will stop the music.
Rhythmbox, Bluetooth and this cron
script must be set up on every machine that
you intend to play music for you. If you do
it on only one box, only that box will start
and stop music as you enter or leave range.
If you set up the system on multiple pieces
of hardware, it will transition the music for
you. When moving out of the range of one
server and into the range of another, the
music automatically will stop in the room
you were in before and start in the room
you are in now.
This is just a simple setup for moving
media around automatically. Multiple
Bluetooth devices could be set up for
different members of the house, and a
priority system could be put in place.
Motion detection using the “motion”
package could be set up to differentiate
areas of your home further with
overlapping Bluetooth. You even could
use facial recognition with help from the
OpenCV Project. There are many places you
can go from here.■
Michael Nugent has spent a good deal of his time designing
large-scale solutions to fit into a tiny budget and leveraging
Linux to fulfill the roles that typically would be filled by large
commercial appliances. Recently, Michael has been working
to design map-reduce clusters and elastic cloud systems for
growing startups in the Silicon Valley area. When not building
systems, he likes sailing, cooking and making things out of other
things. Michael can be reached at [email protected],
and code and notes for this article can be found at
https://github.com/michaelnugent/MusicPuppy.
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ONE KEY
TO RULE
THEM ALL:
GRUB, USB and a
Multiboot Environment
Do you have a spindle of CDs, each of which with a live environment you
use for a specific purpose? Read this article to learn how to combine
them all into one unified boot environment on a USB drive.
ADRIAN HANNAH
I
t’s inevitable. If you work with Linux professionally, you will end up with a bevy of CDs
or USB drives, each with their own live environment, each with a specific purpose. You
likely have some haphazard system for keeping track of which device has what on it
(my personal method was masking tape and pencil). But, there’s no reason to keep doing
this! Improvements in bootloaders (particularly GRUB) let you have live, persistent operating
environments installed on USB drives as well as allowing for multiboot environments. Put this all
together, and you get a single USB drive that replaces the gaggle of devices you used to have.
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GRUB
GRUB, short for Grand Unified Bootloader, is the default bootloader for a vast
majority of Linux distributions. The bootloader is a tiny program that is loaded
into memory immediately when the computer is powered on that knows how to
load data from a nonvolatile source (HDD, USB drive, optical device and so on)
and, in turn, loads an operating system from the specified device.
Setting Up GRUB on USB in Linux
Thanks to the Linux community’s prolific
use of GRUB as the default bootloader,
installing GRUB to the Master Boot Record
for a USB device is incredibly easy. Assume
that you want to call your new volume
“Multipass” and that your target device
resides at /dev/sdb1. First, you need to
create the filesystem:
sudo mkfs.vfat -n Multipass /dev/sdb1
Next, you need to mount the filesystem
and install GRUB:
mount /dev/sdb1 /mnt/
grub-install --no-floppy --root-directory=/mnt /dev/sdb
Now you can add .cfg files to grub.d/ in
order to add/edit/delete menu items to the
boot menu or customize the boot menu.
Setting Up GRUB on USB in Windows
Installing GRUB on a USB device is markedly
different in an environment that doesn’t
natively have GRUB utilities, but it isn’t
impossible. Tools like GRUB4DOS and
WinGRUB are available that give you
access to the same tools in Windows
that are available in Linux. Basically, you
need to find tools to initialize the drive
as a bootable drive and install GRUB to
the device. PeToUSB, GRUB4DOS and
grubinst are the most widely used set of
tools to accomplish this. PeToUSB uses a
simple GUI interface to initialize the USB
device as a bootable device. grubinst is
a GUI installer that installs GRUB to the
USB device. The only reason you need to
download GRUB4DOS is because you need
to copy “grldr” to the USB device. You can
find more detailed instructions on how to
use these tools on-line. But, as Windows
installations are outside the purview of this
publication, I digress.
Adding Distributions
Once you have GRUB set up, you need to
add something to boot. Download your
favorite live CD or app CD, and extract it
using something like the GNOME Archive
Manager. Do not extract this to your USB
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FEATURE One Key to Rule Them All: GRUB, USB and a Multiboot Environment
drive! Instead, extract it to a temporary
location. Once you have performed this
procedure several times, you will notice
that almost all Linux distributions have a
boot directory, and the files within this
directory are the kernel image and vary
from distribution to distribution. Then,
rename the boot directory to something
apropos to the distribution (for instance,
“boot-ubuntu”), and copy it to the USB
device. Aside from the boot folder, there
typically is another folder in these ISOs
that contains the boot image for the OS
(for instance, BackTrack4’s image is stored
in a directory called bt4). Copy this folder
to the USB device as well. You then need
to add an entry in the configuration file so
that this distribution will show up in the
boot menu.
This is where a major schism occurs, and
a little more background knowledge of
GRUB is required. There are two versions
of GRUB, initially referred to as GRUB and
GRUB2, they now are called GRUB Legacy
and GRUB, respectively (GRUB4DOS is a
derivative of GRUB Legacy). There are a
significant number of differences between
the two, but the one that is important to
us right now is that GRUB Legacy uses the
menu.lst file for boot menu configuration,
and GRUB uses grub.cfg. So depending
on the source of the GRUB installation on
your USB device, you will use a different
configuration file.
Some distributions are distributed as a
floppy disk image. Those are the best—all
you have to do is copy the file to the root
of the USB device and add a one-line entry
to the config file.
Even though this takes time, you’re
better off testing each distribution after
installing a new distribution. That way,
if you find an error, it’ll be easier to
troubleshoot the problem. Trust me,
installations can be finicky when you do
things this way, and they can break for
what seems like no good reason.
Adding a Menu Item in grub.cfg
At its most common and basic form, each
menu entry will provide:
1. A user-friendly title.
2. The root filesystem.
3. A kernel image.
4. A boot image or initial ramdisk.
For example:
menuentry "Made Up Distro" { #user-friendly title
set root=(hd0,1) #root filesystem
linux /boot-madeup/vmlinuz0 #the kernel image
initrd /madeup/initrd0.img #the boot image
}
Some distributions take some tweaking
to get them to load properly. For instance,
some live CDs need to be booted into
16-bit mode, and in that case, you would
use linux16 and initrd16 instead.
You can look in the GRUB manual on-line
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for all sorts of boot parameters and
tweaks you can use on the menu item
to make it work, but your best resource
is the grub.cfg that was on the original
ISO for the distribution. Some entries can
become ridiculously complex in order to
work right, like for Fedora:
Adding a Menu Item to menu.lst
The menu.lst file, with regard to menu
items, is quite similar to the grub.cfg
entries. You still specify the user-friendly
title, the root filesystem, and the kernel
and boot images, but the syntax is a little
different. An entry in menu.lst would look
something like this:
linux /fedora1/isolinux/vmlinuz0 live_locale=en_US.UTF-8
➥live_keytable=us live_dir=/fedora1 root=UUID=A716-9810
title Made Up Distro
➥rootfstype=auto ro liveimg quiet rhgb
root (hd0,1)
➥rd_NO_LUKS rd_NO_MD noiswmd
kernel /boot-madeup/vmlinuz0
initrd /madeup/initrd0.img
This is the actual kernel image command
from my own multipass device. It is long
and tedious, but it works.
boot
As with the grub.cfg entries, you can use
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FEATURE One Key to Rule Them All: GRUB, USB and a Multiboot Environment
Listing 1. Sample grub.cfg File
menuentry "Ubuntu Live 11.04 64bit" {
loopback loop /boot/iso/ubuntu-11.04-desktop-amd64.iso
linux (loop)/casper/vmlinuz boot=casper
➥iso-scan/filename=/boot/iso/
➥ubuntu-11.04-desktop-amd64.iso noeject noprompt-initrd (loop)/casper/initrd.lz
}
menuentry "Ubuntu Live 9.10 32bit" {
loopback loop /boot/iso/ubuntu-9.10-desktop-i386.iso
linux (loop)/casper/vmlinuz boot=casper
iso-scan/filename=/boot/iso/ubuntu-9.10-desktop-i386.iso
➥noeject noprompt-initrd (loop)/casper/initrd.lz
}
menuentry "Ubuntu Live 9.10 64bit" {
loopback loop /boot/iso/ubuntu-9.10-desktop-amd64.iso
linux (loop)/casper/vmlinuz boot=casper
iso-scan/filename=/boot/iso/ubuntu-9.10-desktop-amd64.iso
➥noeject noprompt-initrd (loop)/casper/initrd.lz
}
menuentry "Grml small 2009.10" {
loopback loop /boot/iso/grml-small_2009.10.iso
linux (loop)/boot/grmlsmall/linux26 findiso=/boot/
➥iso/grml-small_2009.10.iso apm=power-off lang=us vga=791
➥boot=live nomce noeject noprompt -initrd (loop)/boot/grmlsmall/initrd.gz
}
menuentry "tinycore" {
loopback loop /boot/iso/tinycore_2.3.1.iso
linux (loop)/boot/bzImage -initrd (loop)/boot/tinycore.gz
}
menuentry "Netinstall 32 preseed" {
loopback loop /boot/iso/mini.iso
linux (loop)/linux auto
url=http://www.panticz.de/pxe/preseed/preseed.seed locale=en_US
➥console-setup/layoutcode=de
netcfg/choose_interface=eth0 debconf/priority=critical -initrd (loop)/initrd.gz
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}
menuentry "debian-installer-amd64.iso" {
loopback loop /boot/iso/debian-installer-amd64.iso
linux (loop)/linux vga=normal -initrd (loop)/initrd.gz
}
menuentry "BackTrack 4" {
linux /boot/bt4/boot/vmlinuz BOOT=casper boot=casper
➥nopersistent rw vga=0x317 -initrd /boot/bt4/boot/initrd.gz
}
menuentry "Memory test (memtest86+)" {
linux16 /boot/img/memtest86+.bin
}
menuentry "BackTrack ERR" {
loopback loop /boot/iso/bt4-pre-final.iso
linux (loop)/boot/vmlinuz find_iso/filename=/boot/iso/
➥bt4-pre-final.iso BOOT=casper boot=casper
➥nopersistent rw vga=0x317-initrd (loop)/boot/initrd.gz
}
menuentry "XBMC ERR" {
loopback loop /boot/iso/XBMCLive.iso
linux (loop)/vmlinuz boot=cd isofrom=/dev/sda1/boot/iso/
➥XBMCLive.iso xbmc=nvidia,nodiskmount,tempfs,setvolume
➥loglevel=0 -initrd (loop)/initrd0.img
}
menuentry "netboot.me" {
loopback loop /boot/iso/netbootme.iso
linux16 (loop)/GPXE.KRN
}
menuentry "debian installer amd64 netboot XEN pressed" {
linux /boot/debian/linux auto
preseed/url=http://www.panticz.de/pxe/preseed/xen.seed
➥locale=en_US console-setup/layoutcode=de netcfg/
➥choose_interface=eth0 debconf/priority=critical -initrd /boot/debian/initrd.gz
}
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FEATURE One Key to Rule Them All: GRUB, USB and a Multiboot Environment
many more commands than you can use in
menu.lst, and you can make a lot of tweaks
to make a nonfunctional entry suddenly work.
ISO Loopback
It all seems pretty daunting, no? Don’t you
wish there were a way to dump all your ISO
files onto one disk and then mount them
all? Your wish is granted! With GRUB2,
we were introduced to the loopback boot
option. This allows you to use GRUB to
mount an ISO file and boot from it as if
it were a physical piece of media. All you
have to do for the menu entries is add a
loopback command and then adjust the
linux and initrd commands:
menuentry "Made Up Distro" { #user-friendly title
set root=(hd0,1) #root filesystem
loopback loop "/madeup.iso"
linux (loop)/boot/vmlinuz0 #the kernel image
initrd (loop)/initrd0.img #the boot image
}
GRUB then mounts the ISO file and boots
accordingly. Note that you still may need to
add some arguments to either command to
get it to boot properly. Unfortunately, this
doesn’t work for all ISO files. If you can’t
get the loopback to work for an ISO, you
have to load it the old-fashioned way as
described above.
Customizing the Boot Menu
What good would a fancy tool like this be
if you couldn’t customize it to your liking?
The default boot menu is white text on
black background, which, let’s face it, is
boring. In your config file, you can specify
a background image or color, text color,
highlight color, alternate text for your menu
entries, and the list goes on.
Set the Background Image
First, if you are using GRUB4DOS, the
background picture has to be converted
to 640x480 and 14-color, so you need
to make sure that whatever you’re using
will look good under those constraints.
GRUB2 has a bit more-advanced rendering
capability, and it can handle JPG-, TGA- and
PNG-formatted pictures as long as they are
in RGB mode and not indexed mode.
The basic process for doing this is to
scale and crop the image to your liking,
limit the number of colors in the image
palette to 14, save the image as an xpm
file, and gzip it. For a more in-depth
explanation of this process, I will use
GIMP, although there are a number of
other ways to do this.
After opening the image in GIMP,
use a combination of scaling the image
(Image→Scale Image) and the crop tool
to make the image 640x480. To drop the
number of palette colors in the image,
click Image→Mode→Indexed, and choose
“Generate optimum palette” with 14
colors. That’s all there is to it. You can do
other things to the image to make it look
better in 14 colors:
nFilters→Blur→Selective Gaussian Blur: this
smooths out the image without losing detail.
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nColors→Posterize: this turns subtle
differences in color into a large field of a
single color. This is done smoothly, which
makes the image look better in 14 colors.
nColors→Levels→Auto: this increases
the contrast of the image, lessening the
number of colors used in the image.
nColors→Map→Gradient Map: maps
the existing colors in your image into
a gradient, essentially minimizing the
colors used.
Once you’ve got your image the way you
want it, save it as an XPM image file, then
gzip the XPM file. You’ll end up with a file
named something like image.xpm.gz. Move
this file to your USB device.
If you are running GRUB4DOS, look in
menu.lst for a line something similar to this:
Set the Menu and Highlight Color
You also can adjust the color of the menu
text itself. You can adjust two separate
values: the normal color (consisting of
most of the text and the menu border)
and the highlight color (the colors for
the item currently selected in the menu
list). Each of these values consists of
two colors: the foreground and the
background. Colors you can choose
from include black, dark-gray, light-gray,
white, brown, yellow, red, light-red,
blue, light-blue, green, light-green, cyan,
light-cyan, magenta and light-magenta. If
black is chosen as the background color,
it will show as transparent.
The command to adjust the colors
in menu.lst for GRUB4DOS is color,
followed by the normal color and then the
highlight color. Specify the foreground and
background colors by using a forward slash.
For example:
splashimage splash.xpm.gz
color white/black white/blue
If you find it, replace the splash.xpm.gz
with the path and filename of your file.
Otherwise, add the line.
If you are running GRUB2, open grub.cfg
and find a line that looks something like this:
GRUB_BACKGROUND=splash.xpm.gz
If it exists, replace the image name with
the path and filename for your image.
Otherwise, add the line, then run:
The above signifies white text on a
transparent background, and the highlighted
text is white on a blue background.
GRUB2 uses two variables in grub.cfg
to accomplish the same thing. These
variables are COLOR_NORMAL and
COLOR_HIGHLIGHT. Again, use the
forward slash to separate foreground color
from background color:
COLOR_NORMAL="white/black"
update-grub
COLOR_HIGHLIGHT="white/blue"
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FEATURE One Key to Rule Them All: GRUB, USB and a Multiboot Environment
Change the Text Font
As far as I’ve been able to discern,
you can change the font used in the
menu only if you are using GRUB2. To
accomplish this, you need to utilize one of
the many nifty tools that come with grub:
grub-mkfont. Assuming you already
have the font and you know where the
font file resides, you simply need to run
grub-mkfont, and specify the location
of the font file, the destination for the
grub font file and the size you want the
text to be in points. For example:
menu to your heart’s content.
I was first introduced to the concept
of a multiboot USB device several years
ago when the only way to set it up was
manually with a lot of guessing and
checking. I don’t mind telling you, it was
a royal pain to get anything working, let
alone be elegant. As time goes by, utilities
to help you set them up have emerged,
and they’ve gotten better. What took me
several hours to set up two years ago,
took me only about 15 minutes this time
around (and that includes the time to
download the ISOs). ■
sudo grub-mkfont --output=/path/to/usb_device/comicsans.pf2 --size=14
/usr/share/fonts/comicsans.ttf
Then, in your grub.cfg file, add the
variable GRUB_FONT and set it to the
path and name of the grub font file you
just created:
GRUB_FONT=/path/to/usb_device/comicsans.pf2
Applications to Automate the Process
Take everything I’ve taught you up to this
point and throw it out the window! There
are a number of different applications
for all the major operating systems
that easily will replicate the previously
outlined procedure with little to no fuss.
YUMI and SARDU are the top picks for
generating a multipass in Windows, and
MultiSystem is the tool of choice in Linux.
Each of these applications has a handy
GUI that walks you through adding all
the images you want and customizing the
Adrian Hannah has spent the last 15 years bashing keyboards to make
computers do what he tells them. He currently is working as a system
administrator for the federal government. He is a jack of all trades and
a master of none. Find out more at http://about.me/adrianhannah.
Resources
Windows Resources for GRUB:
http://sourceforge.net/projects/grub4dos/
files and http://www.gocoding.com/
page.php?al=petousb
Multisystem (original site in French):
http://liveusb.info/dotclear
Multisystem (via Pendrivelinux.com):
http://www.pendrivelinux.com/
multiboot-create-a-multiboot-usb-from-linux
YUMI: http://www.pendrivelinux.com/
yumi-multiboot-usb-creator
SARDU: http://www.sarducd.it
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OLPC: Are We
There Yet?
An update on the One Laptop Per Child Project. SAMEER VERMA
Just the other day, I ran into someone in the
parking lot, who looked at the silly-looking
green laptop slung across my shoulder and
said “Didn’t the founder of that project ditch
and disappear?” News travels fast, no matter
where it comes from, and no matter how
wrong it is. I’m amused.
Of course, I am talking about the One
Laptop per Child (OLPC) Project, founded
by Professor Nicholas Negroponte in 2005.
Conceived as a learning project at MIT back
in the early 1980s (with Professor Seymour
Papert), it morphed into a laptop project in
Cambodia in 1999 and eventually into the
current OLPC Project in 2005. OLPC currently
has more than two million laptops in the
hands of children in more than 25 languages
in more than 40 countries.
I got involved in July 2007, when I first
saw the XO laptop at OSCON (thanks to Rob
Savoye) and instantly fell in love with it. I
quickly signed up with the developer program
and got myself a beta machine. However,
unlike my short-lived affairs with other
gadgets, I’ve hung onto this one for more
than four years now. Along the way, I became
the de facto organizer for the OLPC San
Francisco volunteer community. OLPC also has
found a spot on my research agenda. I now
run projects in Jamaica, India and Tuva (yes,
that Tuva, of Richard Feynman fame), and I
help out with others in Armenia, Madagascar,
Morocco and a whole bunch of other places.
Making technology work in remote places
has been a welcome challenge. Making it
work for children the world over has been a
fulfilling experience.
Hardware
Speaking of laptops, the lean, green children’s
machine is quite the icon. It gathers crowds
with little effort. It brings forth the inner child
in many a tough adult. Let’s take a peek into
what’s under the plastic. Table 1 shows the
different incarnations of the OLPC XO laptop.
The XO has many cool features. It is
rugged, solar-chargeable, has a sunlightreadable screen, supports mesh networking
and has a very aggressive suspend-resume
cycle, but the importance of these features
supersedes their coolness when deployed in
the field. One of my projects is in Bhagmalpur,
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Table 1. XO Laptop Hardware Evolution
MACHINE
CPU
RAM
STORAGE
FORM FACTOR
XO-1
AMD Geode LX 700 (x86)
at 433MHz
256MB
1024MB NAND Flash
JFFS2 filesystem
Laptop (green, with
membrane keyboard
XO-1
AMD Geode LX 700 (x86)
at 433 MHz
256MB
2048MB NAND Flash
JFFS2 filesystem
Laptop (red, with
membrane keyboard)
XO-1.5
VIA C7-M (x86) at 1GHz
(variable)
1024MB
4GB microSD Ext4
filesystem
Laptop (green, with
membrane keyboard)
XO-1.5HS
VIA C7-M (x86) at 1GHz
(variable)
1024MB
4GB microSD Ext4
filesystem
Laptop (blue, with Netbook
keyboard)
XO-1.75
Marvell Armada 610 (ARM)
SoC at 1GHz (variable)
512MB
Undecided (still in testing)
Laptop
XO-3
ARM (proposed)
Undecided
Undecided
Tablet
a cow!), and I am glad to be able to give
back. Bhagmalpur is beautiful, but it has its
own problems. Electricity is elusive at best.
There’s no Wi-Fi. Internet access rarely works,
and when it does, it trickles. There are no
classrooms; the kids sit under a tree. This is
where we see the real benefits of sunlightreadable screens, solar chargers, under-a-tree
mesh-networking technology and aggressive
suspend-resume cycles that conserve every
fraction of a watt. All of this made possible
by a combination of free and open-source
software.
Figure 1. Red-Green-Blue Spectrum of XOs
a rural village in northern India. Bhagmalpur
is close to my heart. A part of my family
lives there, and keeping up with the village
helps me stay grounded in their realities. I
have learned much from them (I can milk
Internet in a Box
Another neat setup we have in Bhagmalpur
is an off-line server. Remember SneakerNet
from the days of tapes and floppies?
SneakerNet is a wonderful concept. You can
think of it as a kind of mirroring with a very
high latency. Given that about 70% of the
world’s population still is not on the public
Internet, SneakerNet approaches become
important stopgap measures. OLPC has a
Fedora-based image (called the XS) that is
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designed to run an off-line server at the local
school, village or library. Think of it as an
“Internet in a box”. Yes, it’s not the entire
Internet, but storage is cheap these days.
You can pack plenty of content on a 2TB
drive, be it Khan Academy videos, TED Talks,
books from Project Gutenberg, the Internet
Archive, Wikipedia and so on. This approach
acts as a stopgap, so that we can get the
kids access to some information at least for
now. Eventually, when the Internet gets there
24/7, this server can continue to function as
a conduit to the outside.
The school server runs on x86 machines
(ours in Bhagmalpur draws 8 watts) and
provides a plethora of services. The design
of this server revolves around Moodle, a
learning management system. Some of the
administrative capabilities also are plugged
in to Moodle, so teachers don’t have to
drop to a command line to administer the
server. Other services that run on the XS
are Apache, PHP and PostgreSQL (to run
Moodle), ejabberd (to provide XMPP-based
collaborative services), Squid, DHCP, DNS
and a few others. In the Bhagmalpur setup,
we also use Munin to keep an eye on server
health and OpenVPN to tunnel back to San
Francisco to pull logs and to push content via
rsync. The server not only serves up content
and courses, but it also seamlessly backs
up each laptop’s datastore, pushes both
OS and application updates, manages theft
deterrence, network access and more.
The XS is designed to follow a curricular
model, complete with courses, teachers,
students, enrollment and assessment all
Figure 2. Garima in Bhagmalpur
managed via Moodle. However, in some
instances, a curricular model isn’t suitable.
Sometimes we simply don’t have a functional
school in the neighborhood. In such cases,
a reference library is more apt. There’s a
parallel effort to fill the need for an offline digital library, but without a specific
curricular underpinning. Pathagar (in Bengali,
path=lesson, agar=repository) is a Djangobased digital library that serves up an XML
catalog of content using the Open Publication
Distribution System (OPDS). Content can be
searched and downloaded using a browser
or custom reader. Uruguay has been using
Pathagar in production for some time now.
We are testing it for Bhagmalpur (using
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Debian Squeeze on a SheevaPlug) right now
and hope to put it into production soon.
Deployments
OLPC projects come in all sizes. Projects that
implement laptops in the field are called
deployments. There are large, top-down
OLPC-managed deployments and small
third-party deployments managed by NGOs
and volunteer communities. As Professor
Negroponte puts it, uppercase OLPC is the
“official” effort, whereas lowercase olpc is
the community effort. Of course, one without
the other wouldn’t get very far. Uppercase
deployments, like Peru, are the largest with
almost a million machines. Uruguay follows
closely with 100% saturation at the primary
school level, and Rwanda recently crossed the
100,000 laptop mark. In the lowercase olpc
realm there are several projects with much
less volume, but nevertheless, a strong intent.
Some are in the hundreds, like my projects
with the University of the West Indies in
Jamaica. Others are in the tens, like the effort
in Bhagmalpur. We even have some efforts
with a single eBay-bought XO laptop lighting
up someone’s world somewhere. It’s a spark
that holds the potential to ignite.
Keeping track of smaller deployments
is difficult. We have two planet feeds to
keep track of various deployments (see
Resources). We also have an effort to
map the community at large—who they
are, where they live, what they do and
whom they work with. olpcMAP.net maps
out deployments, projects and volunteers
from Armenia to Zambia, with language
translation efforts from Amazigh to Zulu.
Kids Like Sugar
Looking past the hardware, one of the
key features of OLPC deployments is its
software—more precisely, its software as
a learning platform. Sugar is a learning
platform designed for children. It originally
was designed for the OLPC XO laptop, but
since then it has grown to run on most
Netbooks and PCs. Sugar is used by more
than two million students in Peru, Uruguay,
Rwanda, Nepal, the United States and more
than 40 other countries.
Sugar is distributed as free software,
released under GPL v2. It is available in more
than 25 languages, although the translation
infrastructure has 132 languages in various
stages of completion. Sugar is a collaborative
learning platform that promotes collaborative
learning. Sugar also can be viewed as a
graphical user interface and a collection of
software applications (called Activities) that
give children a rich environment for learning.
The Sugar user interface is very simple.
It has a “low floor”, so that even children
as young as ages two and three can start
to use it. At the same time, it puts no limit
on what they can achieve. Children can use
Sugar to reach very complex ideas. They
are not bound by its simplicity; rather, they
use its simplicity as a catalyst for growth.
Sugar presents no “ceiling” to the learner.
In fact, each application ships with its
source code (usually Python) and can be
viewed and modified in much the same
way as with HTML.
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Figure 3. Sugar View Source Option
Sugar has built-in mechanisms for
collaboration using an XMPP-based layer
that allows for applications to share data
across the network. For instance, the Write
Activity (based on AbiWord) can “talk” to
another child’s Write Activity over the network
and allow for real-time, collaborative word
processing. This is very much like what you
may see with Google Docs, but without
Google in the middle. It’s agnostic of the
network layer, so the collaboration can work
between two laptops meshed together under
a tree or two laptops connected over the
Internet reaching across continents.
Sugar maintains a journal, a diary of sorts,
of everything a child does. It is a record of
both what things learners make and how they
made them. This journal runs on top of an
XML datastore written in Python and works
as a flat, time-based listing, sortable by time,
topic, mime-type and so on, and it allows
children to resume work where they left off.
The journal also allows for reflecting upon
one’s work by taking notes once each activity
is done. Looking at these notes over time
should give students a sense of how their
work has evolved. In all, Sugar is not about
instruction; it is about learning.
Sugar Activities come in many flavors.
Some, such as the Browse activity (based on
Firefox) rely on the network extensively, while
others, such as the Wikipedia bundle, are
completely off-line. Then, there’s the physical
computing kind of activity. Activities like
Scratch and Turtle Art interface with the 3-D
real world using Arduino boards and LEGO
robots. Taking a cue from the Uruguayans
who are building Arduino-based XO robots
and the Peruvians who are distributing 92,000
LEGO robotics kits to their schools, we have
started exploring the use of LEGO WeDo
robotics kits in Jamaica. The charge is being
led by a ten-year-old Jamaican kid!
Then there is the Measure activity, an
oscilloscope of sorts, reading from the
microphone port for sensor data. How many
overtones do throat singers of Tuva produce?
Measure can tell you—think lemon batteries,
conductive playdough and electromagnetic
Figure 4. Scratch and LEGO WeDo Robot
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speedometers. Now we are talking real
education! The list goes on, but you can
explore all of these on the Sugar Activities
repository.
On the technical side, all of OLPC’s XO
images are Fedora-based (Fedora 14 at the
time of this writing). Sugar runs on top of
Fedora (OLPC also packs a GNOME option
for older kids). Sugar is primarily written
in Python, using PyGTK extensively. Sugar
uses an interesting security spec called
Bitfrost. Creating Activities in Sugar is
easy once you understand Sugar’s human
interface guidelines. Many existing GTK
apps can be “sugarized” easily as well.
Although those details are out of the
LJ211-November2011.indd 103
scope of this article, a good place to start
is James Simmons’ book Make Your Own
Sugar Activities! (see Resources).
Sugar Labs is the current home of the
Sugar Project. Started as a spin-off from
OLPC, it is headed by Walter Bender as its
Executive Director. Sugar Labs is a volunteerdriven, nonprofit organization, and a member
project of the Software Freedom Conservancy.
It coordinates volunteers—an international
community of teachers, software developers,
artists, writers, parents and children—who
are passionate about providing educational
opportunities to children through the Sugar
Learning Platform. Children as young as 12
years old have written Sugar Activities. When
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a 12-year-old developer walked into one of
our OLPC San Francisco meetings, we thought
he was lost and looking for his parents!
Conclusion
In all, the project is alive and well. Every
single laptop out there counts as one more
platform of information—both for access
and for creation. Young minds all over are
starting to get opportunities to connect the
dots with the rest of the world. These are
not cheap laptops. These are little Linuxpowered revolution machines, and the
revolution is on. So, come and join us. Bring
meaningful and participatory education to
millions. Stand up and make your mark for
those who cannot. Help them solve their
own problems. Start tiny sparks, so that
some day, we may light up the world.
Before I wrap up, I should set the record
straight. I have been approached by several
people who ask, “Didn’t OLPC switch over to
Windows?” This myth also is a popular point
of contention on sites like Slashdot to which
John Waltington (OLPC’s VP for Hardware
Engineering) replied: “Linux has shipped, and
will continue to ship, on every XO produced.
You can believe random commenters, or
you can believe the person who signs off on
every SKU produced.” Two million+ laptops
all shipped with Linux. There you have it,
straight from the man.
Acknowledgements
I would like to acknowledge the input and
suggestions from Walter Bender, Christoph
Derndorfer, Adam Holt and Mike Lee.■
Sameer Verma is a professor of Information Systems in the College
of Business at San Francisco State University in San Francisco,
California. He is also the founder and chief organizer of the OLPC San
Francisco volunteer community. All of his computers run Linux—
even the one in his car. Track him down at http://verma.sfsu.edu.
Resources
One Laptop Per Child: http://laptop.org
Sugar Labs: http://sugarlabs.org
OLPC Planet: http://planet.laptop.org
Sugar Labs Planet: http://planet.sugarlabs.org
Sugar Translation: http://translate.sugarlabs.org
Sugar Activities Repository:
http://activities.sugarlabs.org
OLPC San Francisco: http://olpcsf.org
Bhagmalpur Project:
http://bhagmalpur.wordpress.com
Jamaica Projects: http://olpcjamaica.org.jm
Tuva Project: http://olpctuva.wordpress.com
Scratch and LEGO WeDo:
http://info.scratch.mit.edu/WeDo
James Simmons’ Make Your Own Sugar
Activities!: http://en.flossmanuals.net/
make-your-own-sugar-activities
John Waltington’s Comment on Slashdot:
http://hardware.slashdot.org/
comments.pl?sid=1941464&cid=34810832
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Creating a vDSO:
the Colonel’s
Other Chicken
vDSO, or virtual dynamic shared object, is a clever feature of
the Linux kernel used to speed up certain system calls and
access data in separate memory segments efficiently. MATT DAVIS
A vDSO (virtual dynamic shared object) is an
alternative to the somewhat cycle-expensive
system call interface that the GNU/Linux
kernel provides. But, before I explain how to
cook up your own vDSO, in this brief jaunt
down operating system lane, I cover some
basics of vDSOs, what they are and why they
are useful. The main purpose of this article is
to illustrate how to add a custom vDSO to a
Linux kernel and then how to use the fruits
of your labor. This is not intended to be a
vDSO 101; if you would like more in-depth
information, see the links in the Resources
section of this article.
vDSO Basics
The traditional mechanism of communication
between userland applications and the kernel
is something called a system call. Syscalls are
implemented as software interrupts providing
the userland application with some kernel
functionality. For instance, gettimeofday()
and fork() are both system calls. The reason
syscalls exist is due to the fact that the Linux
kernel is divided into two primary segments of
memory: userland and kernel land. Userland is
where common programs, including dæmons
and servers, execute. Kernel land is where the
kernel schedules processes and does all of
its nifty kernel-specific magic. This division in
memory acts as a safety barrier between user
applications and the kernel. The only way a
user application even can touch the kernel
is via system call communication. Therefore,
the robustness and integrity of the kernel
is protected by the limited set of routines it
provides userland access to, the system calls.
To accomplish a syscall, the kernel must
flip-flop memory contexts: storing the
userland CPU registers, looking up the syscall
in the interrupt vector of syscalls (the syscall
vector is initialized at boot time) and then
processing the syscall. Once the syscall has
been processed in kernel land, the kernel
must restore the registers from the previously
stored userland context. This completes the
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syscall; however, as you can imagine, this
is not a tax-free series of events. Numerous
cycles are spun just to make these special
kinds of function calls.
Although this segmentation sounds
great for the security world, it does not
always provide the most efficient means
of communication. Certain functions that
do not write any data and merely return
a value stored in the kernel, such as
gettimeofday(), are relatively safe in
nature and provide no threat to the kernel
from the requesting userland application.
Wouldn’t it be nice if you could make safe
functions not have to do the memory-barrier
tango? Well, you can—with vDSO!
You’re probably wondering how a vDSO
gets placed into a program in the first
place, over the traditional syscall. Well,
vDSO hooks are provided via the glibc
library. The linker will link in the glibc vDSO
functionality, provided that such a routine
has an accompanying vDSO version, such
as gettimeofday(). When your program
executes, if your kernel does not have vDSO
support, a traditional syscall will be made. This
test of vDSO functionality is provided by the
code linked from glibc. Of course, you don’t
want to hack up glibc just so you can have
your home-brewed vDSO run. The method
for creating a vDSO described below does not
require modification of glibc; instead it relies
on hacking up the kernel, as expected.
Cluck, Cluck...vDSO
These safe syscalls can be implemented
on a page of virtual memory that can be
mapped into each running process’ memory.
This implementation is similar to how other
dynamically shared objects are mapped into a
process, such as shared libraries. In fact, if you
were to extract the page from memory and
disassemble it, the result is a shared-library
ELF. In other words, the vDSO is just a shared
library (sorry to blow the magic for you). With
this page of safe syscall routines resident
to the userland application, a program can
make the call and not have to endure the
overhead of the memory-hopping between
user and kernel segments that a traditional
syscall would require. One perfect example
is gettimeofday(). This routine not only
is timing-sensitive, but it often is a routine
that is used at a high frequency. Consider
that it takes the kernel time to hop memory
segments. Once the clock is sampled, cycles
must be spent to flip memory segments.
The longer this takes, the less accurate the
returned time value will be.
Let’s Get Frying’
Enough with theory and all that mumbojumbo, let’s get to what this article is all
about—making your own vDSO. This article
assumes a 64-bit x86 processor using the
2.6.37 Linux kernel. You’ll probably be
surprised at how easy this is. It is even less
involved than making a traditional syscall.
The confusing part comes when trying to
share data via variables between kernel
and userland.
Let’s create a syscall that does something
basic—say, produce an integer value of,
oh, the number of the beast, 666. For all
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instructive purposes, let’s call this function,
number_of_the_beast(). Because I’m not
sure that the true number of the beast
is static (hey, beasts might change), let’s
make this function do just that, tell us
the number of the beast. (It could be like
a president and change every few years.)
Create a file in linux-2.6.37/arch/x86/vdso/
called vnumber_of_the_beast.c, and inside
there, define your function:
such as function calls, that do not resolve
until runtime. The word “weak” simply
means the symbol can be overridden. If
the symbol does not exist, no warnings
are issued, as no symbol is acceptable
in this case. The alias associates the
local _ _vdso_number_of_the_beast
to the world-accessible version,
number_of_the_beast. Add the following
piece just after the function previously added:
#include <asm/linkage.h>
int number_of_the_beast(void)
_ _attribute_ _((weak, alias("_ _vdso_number_of_the_beast")));
notrace int _ _vdso_number_of_the_beast(void)
The only interesting/unusual thing here
is the notrace macro. It is defined in
linux-2.6.37/arch/x86/include/asm/linkage.h
as being:
Now, you just need to toss in some pieces to
the linker script so that when the kernel builds,
your code will get built and linked into the
vdso.so shared object. That is what you will
use for your hook when writing code that uses
the vDSO. Now, bust out your text editor and
modify linux-2.6.37/arch/x86/vdso/vdso.lds.S to
add the function names you just added:
#define notrace _ _attribute_ _((no_instrument_function))
VERSION {
{
return 0xDEAD - 56339;
}
LINUX_2.6 {
The above GNU extension tells the gcc
compiler that when it compiles the function
to exclude hooks supporting profiling
feedback. Profiling feedback can be built in,
if the notrace macro is removed and if the
gcc flag -finstrument-functions was
passed to the gcc at compile time (see the
GCC Manual, listed in Resources).
You also need to tell the compiler to
link a userland-accessible function called
number_of_the_beast, which is also a
weak symbol. Weak symbols represent data,
global:
clock_gettime;
_ _vdso_clock_gettime;
gettimeofday;
_ _vdso_gettimeofday;
getcpu;
_ _vdso_getcpu;
/* ADD YOUR VDSO STUFF HERE */
number_of_the_beast;
_ _vdso_number_of_the_beast;
local: *;
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};
}
One more thing, you need to tell the
compiler actually to compile the information
in vnumber_of_the_beast.c. To do
this, just toss some information into the
Makefile located in linux-2.6.37/arch/
x86/vdso/Makefile. Add the name of the
file, with a .o instead of a .c extension.
And, through make wizardry and black
magic, it will be compiled at compile time.
Again, break out the text editor, and add
the name to the list of object files for the
variable vobjs-y. Your result should look
something similar to the following:
# files to link into the vdso
vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
➥vvar.o vnumber_of_the_beast.o
And Now Some Special Sauce
If the vDSO is operating in userland, how
do you access kernel-land variables? After
all, if vDSOs are supposed to provide kernel
information, don’t they have to trip the
userland/kernel-land memory segment?
And, wouldn’t that flip-flopping of memory
context render a vDSO useless? Well, it
all depends how the userland version, the
vDSO version, accesses the kernel data. For
gettimeofday(), a special time variable
is mapped into memory where the kernel
updates it and the userland (vDSO version)
can read it. The kernel merely copies what
it knows about time into that variable, and
when a vDSO is made, that call just reads
the information saving the overhead of
crossing memory segments. The addition or
access of a kernel variable is fairly involved
as compared to a basic vDSO function, but
because the purpose of a vDSO is to access
kernel information, such as that provided
in variables, I probably should give a quick
overview of doing that.
For illustrative purposes, let’s add a value
that lives in kernel land but is read from
userland. Sure, I said earlier that this mystical
number might change and you should
implement a function to return it. Well, you
have a function, but all you know now is
the value and not what it might change to
in the future. Let’s make the function return
a value, nonconstant. Wow, this use case is
becoming really unusual. To elaborate, let’s
update this variable as the kernel requests.
The kernel will update the vDSO variables in
the update_vsyscall() function located
in linux-2.6.37/arch/x86/kernel.
If you were to declare it const int
vnotb = 666;, the value captured there
would not be set (more on this later).
Let’s define the value to be, in fact, the
mysterious number of the beast itself, which
I will call vnotb. This number will reside
in kernel land, as so many other useful
values, such as time, which the efficient
gettimeofday() vDSO will obtain. This is
where the true magic of vDSOs lie.
Let’s remain in linux-2.6.37/arch/x86/vdso
and modify all the goodies here. First, declare
the variable via the VEXTERN() macro. In
vextern.h, add your declaration alongside all
the other declarations:
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INDEPTH
VEXTERN(vnotb)
This macro will create a variable that is a
pointer to the value you care about and is
prefixed with vdso_. In essence, you have
declared vnotb as int *vdso_vnotb;.
vextern.h mentions that:
Any kernel variables used in the vDSO
must be exported in the main kernel’s
vmlinux.lds.S/vsyscall.h/proper_ _section
and put into vextern.h and be referenced
as a pointer with vdso prefix. The main
kernel later fills in the values (comment
in linux-2.6.37/arch/x86/vdso/vextern.h).
Now that you have some of the vDSO code
in place, the userland stuff and the kerneluserland mapping, let’s make use of it. In the
function vget_number_of_the_beast(),
let’s return the value:
notrace int _ _vdso_number_of_the_beast(void)
{
return *vdso_vnotb;
}
Don’t forget to add the header that
declares that value, vextern.h as well as
an additional header that will resolve some
data referenced by the latter, vgtod.h:
#include <asm/vgtod.h>
#include "vextern.h"
To wrap things up, you need to let the
kernel know about this variable so it can
pump data into it. You need the kernel
to give userland a value. Well, you have it
mapped at the address specified above, but
that is rather pointless, unless Mr Sanders,
the colonel, doesn’t push some data into it.
You need to go up one directory (yes, this
isn’t the most trivial of processes). Hop into
linux-2.6.37/arch/x86/kernel. You need to let
the linker know of this value, so it can map
between kernel and userland, so you probably
should rock that. Modify vmlinux.lds.S, and
add the following after the vgetcpu_mode
piece (note that adding it after or before
vgetcpu_mode isn’t necessary, but it’s an
easy place to find things):
.vnotb : AT(VLOAD(.vnotb)) {
*(.vnotb)
}
vnotb = VVIRT(.vnotb);
This links the vnotb symbol with the
variable vnotb. This sets up the variable in
the address space for kernel land to access
and write to. The macros above, AT, VLOAD
and VVIRT deal with modifying addresses
so that the proper piece of data, at the
vnotb, is referenced.
Now, you need to declare the value that
the kernel land will write to. In linux-2.6.37/
arch/x86/include/asm/vsyscall.h declare this
puppy and its section that will be inserted
via the above linker script entry you most
recently added:
#define _ _section_vnotb _ _attribute_ _ ((unused,
➥_ _section_ _ (".vnotb"), aligned(16)))
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INDEPTH
In this file, as mentioned, you also will
declare the kernel-land variable to which
the kernel will write. To keep things slightly
more readable, associate your variable next
to the vgetcpu_mode declaration:
extern int vnotb;
You also will define a value the kernel can
read (I don’t use this in my example, but if
the kernel needs to read the value, this is
the variable to read):
extern int _ _vnotb;
update_vsyscall() routine in linux-2.6.37/arch/
x86/kernel/vsyscall_64.c with:
vnotb = 666;
This statement is defining the value
declared previously in vsyscall.h.
Compiling, Linking and Running
Wait, is that all there is to adding a vDSO?
Um, yes. Of course, if the function was
something supported by the C library (glibc,
in our case), you can hack that to do the
detection of vDSO and then the actual
call. However, I mentioned we wouldn’t be
Now let’s put this stuff in code and give
it a value. The kernel will write the value
via the writable vnotb, and you also can
read it from the shared memory between
kernel and userland via _ _vnotb. You will
write the value in the kernel-land version of
the variable, which is writable. In linux-2.6.37/
arch/x86/kernel/vsyscall_64.c, preferably
after all of the #include headers and just
after the piece: int _ _vgetcpu_mode
_ _section_vgetcpu_mode;, add the
following:
int _ _vnotb _ _section_vnotb;
Remember, you did a trick with the linker
setting the value. If you set the value globally,
as you would for an extern, you would not
get a value, the linker would override it.
You need to set this value at runtime and
not statically at compile time. To set this
value as the kernel updates, modify the
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INDEPTH
Listing 1. Extracting the vDSO from a Running Kernel
/* extract_vdso.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char **argv)
{
char
buf[256], *mem;
const char *range_name;
FILE
*rd, *wr;
long long
start_addr, end_addr;
/* Open file for writing the vdso data to */
if (argc != 3)
{
fprintf(stderr,
"Usage: %s <file> <string>\n"
"\t<file>:
File to write the vdso data to.\n"
"\t<string>: Name of the mapped in region, e.g. vdso\n",
argv[0]);
abort();
}
range_name = argv[2];
if (!(wr = fopen(argv[1], "w")))
{
perror("Error: fopen() - output file");
abort();
}
/* Get this process' memory layout */
if (!(rd = fopen("/proc/self/maps", "r")))
{
perror("Error: fopen() - /proc/self/maps");
abort();
}
/* Find the line in /proc/self/maps that contains
the substring [vdso] * */
while (fgets(buf, sizeof(buf), rd))
{
if (strstr(buf, range_name))
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INDEPTH
break;
}
fclose(rd);
/* Locate the end memory range for [vdso] */
end_addr = strtoll((strchr(buf, '-') + 1), NULL, 16);
/* Terminate the string so we can get the start
address really easily * */
*(strchr(buf, '-')) = '\0';
start_addr = strtoll(buf, NULL, 16);
/* Open up the memory page and extract the vdso */
if (!(rd = fopen("/proc/self/mem", "r")))
{
perror("Error: fopen() - /proc/self/mem");
abort();
}
/* Hop to the vdso portion */
fseek(rd, start_addr, SEEK_SET);
/* Copy the memory locally and then move it to the file */
mem = malloc(end_addr - start_addr);
if (!fread(mem, 1, end_addr - start_addr, rd))
{
perror("Error: read() - /proc/self/mem");
abort();
}
/* Write the data to the specified output file */
if (!fwrite(mem, 1, end_addr - start_addr, wr))
{
perror("Error: fwrite() - output file");
abort();
}
free(mem);
fclose(rd);
fclose(wr);
printf("Start: %p\nEnd:
%p\nBytes: %d\n",
(void *)start_addr, (void *)end_addr, (int)(end_addr ➥start_addr));
return 0;
}
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INDEPTH
hacking glibc. And, you don’t need to
anyway, because getting the code to work
is pretty simple. With the chunks described
above all in place, it’s time to start building.
Just configure and compile your kernel as
you typically would:
make menuconfig
make bzImage
make modules
make modules_install
Now, install and boot your new modified
vDSO kernel. Once that is up and running,
it’s time to test a few things, mainly the
vDSO stuff you just added. Let’s compile a
test case to exercise the vDSO call:
/* notb.c */
#include <stdio.h>
int main(void)
{
int notb = number_of_the_beast();
printf("His number is %d\n", notb);
return 0;
}
Then, compile the code above as:
gcc notb.c -o notb vdso.so
The file you link against is vdso.so,
which provides the symbol resolution
needed to make the kernel call. The kernel
version of number_of_the_beast() is
called, even if the code for that function is
completely different in vdso.so. Where is
vdso.so located? It’s located in the kernel
build directory after building the kernel:
linux-2.6.37/arch/x86/vdso/vdso.so.
At runtime, when a program executes
number_of_the_beast, the kernel
code is called and not the version of
number_of_the_beast() in the vdso.so
file. If you modify the kernel and, say,
have number_of_the_beast() return
42, then unless you load that kernel, you
still will get 666. Even if you compile
the test example above with the newer
modified-to-42 vdso.so.
Another way of getting the vdso.so file is
by writing a program that extracts the vDSO
memory from a running executable. Numerous
sources on-line explain how to do this, but I
briefly describe it here. The vDSO page, which
is mapped into the memory of every running
process, can be in a non-deterministic memory
range of your executing process, thanks to
Linux’s address space layout randomization
(ASLR). To get this address, a running program
can find its memory information from the
file /proc/self/maps. In there, a line with the
text [vdso] exists. That line contains the
address range in the executing process of
the vDSO page. For example, you could run
cat /proc/self/maps.
Note that running this command multiple
times produces different address ranges for
[vdso] thanks to (if your kernel supports it)
address space layout randomization.
The output should look something similar to:
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INDEPTH
...
7fff40d71000-7fff40d72000 r-xp 00000000 00:00 0 [vdso]
...
The above range is showing for the
cat process you just executed that the
address range for the vDSO page is located
starting at 7fff40d71000 and ending at
7fff40d7200. Subtracting the start and
end range, you get 0x1000 or 4096 bytes.
4096 is the page size often used in the
kernel. Listing 1 shows code for extracting
the vDSO from a running kernel, and it is
based on code from the “Examining the
Linux VDSO” article listed in Resources.
A simple dumping of the dynamic object
symbols can be conducted via:
objdump -T vdso.so
Because a shared library is also an elf, the
readelf tool also can be used on vdso.so.
Security Implication
Anytime you dabble with the kernel, you
should consider the security implications. If
you think you can “own” someone by creating
your own vDSO calls, you might want to think
again. Because adding a vDSO requires users
to bake their own kernels, the only people they
could be compromising is their system and the
users on their system. Of course, any dabbling
with kernel resources should be done with
much consideration. Remember, playing with
vDSO goodies occurs in userland; however,
your vDSOs can access kernel data. And,
your kernel can read vDSO data. That can be
a concern, but I’ll leave that up to you as an
exercise for finding anything exploitable.
Finally, this article is just a little one-two
on how to cook up your own vDSO. Now
go make yourself a smoking kernel.■
Matt Davis is a software engineer on leave from his job in the US to
pursue a PhD from the Computer Science Department at the University
of Melbourne, where he is focusing his hackery toward the compiler
field. He has been involved in both the fields of modeling and simulation,
as well as kernel-level high-precision timing. His interests include
coding, compilers, kernels, listening to obnoxious music, consuming
vast quantities of coffee and being social with wulfpax and 757.
Resources
GNU/Linux Kernel. 2.6.37:
http://www.kernel.org
“6.30 Declaring Attributes of Functions”
(GCC Manual): http://gcc.gnu.org/
onlinedocs/gcc/Function-Attributes.html
“Weak Symbol” (Wikipedia):
http://en.wikipedia.org/wiki/Weak_symbol
“Examining the Linux VDSO” (Truth,
Computing and Fail): http://anomit.com/
2010/04/18/examining-the-linux-vdso
Johan Peterson’s “What is linux-gate.so.1?”:
http://www.trilithium.com/johan/2005/08/
linux-gate
Matt Davis’ “Linux syscall, vsyscall, and
vDSO...Oh My!”:
http://davisdoesdownunder.blogspot.com/
2011/02/linux-syscall-vsyscall-and-vdso-oh-my.html
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EOF
Losing Its Way
DOC SEARLS
Why has IBM remained sane while HP’s gone nuts?
One word: engineers.
W
hen I arrived in Silicon Valley,
in August 1985, HP loomed
large—literally. My office was
in Palo Alto Square, on the corner of El
Camino Real and Page Mill Road. Across
the street on another corner was a little
building preserved as the original postgarage location of Hewlett-Packard. (It’s
gone now.) The next block up Page Mill
was the sprawling headquarters for what
Hewlett-Packard had become: the largest
and most prestigious company in the whole
valley and one of the most desirable places
in the world for an engineer to work.
HP in those days was what people called a
“Theory Y” company (http://en.wikipedia.org/
wiki/Theory_X#Theory_Y): a place where
work was as enjoyable as play. (“Theory X”
referred to the more-common form.) Bill
Hewlett and Dave Packard were both alive
and active then, and “The HP Way”
(http://www.hpalumni.org/hp_way.htm)
still meant what it said: “trust and
respect for individuals...high level
of achievement and contribution...
uncompromising integrity...teamwork...
flexibility...innovation...” and so on.
In his autobiography, iWoz, Steve
Wozniac calls the old HP “just the most
perfect company”:
This was in January of 1973, and for an
engineer like me, there was no better
place to work in the world. Unlike a
lot of technology companies, HewlettPackard wasn’t totally run by marketing
people. It really respected its engineers.
And that made sense, because this was
a company that had made engineering
tools for years—meters, oscilloscopes,
power supplies, testers of all types,
even medical equipment. It made all the
things engineers actually used, and it
was a company driven by engineers on
the inside so far as what engineers on
the outside needed. Man I loved that.
The distinction between marketing
people and engineers is the one between
today’s HP and the one that died along
with its founders. You could see it in 1999,
when the instrument business—the original
heart and soul of HP—was spun off. The
name for the new company was Aligent,
which sounds like something you squirt
up your nose so you won’t sneeze. It still
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exists, but who cares? It’s not HP.
Spinning off and anonymizing the soul
of the company was the last thing most
engineers inside HP would have done,
for the simple and obvious reason that
no engineers (or anybody) outside the
company wanted it. The same was true
when HP bought Compaq. Both moves
were typical of “marketing people”, even
as they violated the original function of
marketing, which was finding and serving
the true wants and needs of customers.
One could see the same disconnect—
between marketing fantasy and
engineering reality—in HP’s purchase
of Palm for $1.2 billion in April 2010,
and its announced decision to kill what
was left of Palm’s old business in August
2011. That announcement came at the
same time as the company also revealed
that its entire PC division—including
what it obtained from Compaq (for $25
billion in stock) in 2002—was for sale.
(The marketing spin was “Evaluate Strategic
Alternatives”: http://www.hp.com/hpinfo/
newsroom/press/2011/110818xb.html.)
At that moment, HP still was the world’s
#1 PC vendor, with $40.1 billion in revenue
and $2 billion in operating income for the
most recent fiscal year (Wall Street Journal
http://blogs.wsj.com/digits/2011/09/08/
h-p's-pc-chief-hopes-for-speedy-spinout).
It had a 17.5% market share, with
shipments of 14,888,086 units in Q2 2011
(Gartner: http://www.gartner.com/it/
page.jsp?id=1744216), ahead of Dell
(12.5%), Lenovo (12.0%), Acer (10.9%),
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EOF
ASUS (5.2%) and Toshiba (5.2%). The more
telling difference was in growth. HP’s was
3.0%. Dell’s was 3.3% and ASUS’s was 3.7%,
while Acer was down –20.4% and Toshiba
was down –1.9%. The only bright spot was
Lenovo, which had a whopping 22.5%
growth rate.
And, who’s surprised? Which would you
rather have—a ThinkPad from Lenovo or a
whatever-they’re-called from one of those
other guys? Even given Lenovo’s fainthearted support for Linux, ThinkPads are
the least clone-like of all the “compatible”
PC laptops. Meanwhile, HP’s PCs have
long been nearly anonymous but for the
company logo they bear. Without that
small bit of value, what’s their distinction?
The answer is none, which is why no other
PC maker has bought the division. They
already make no-name computers. So,
by announcing the hunt for “strategic
alternatives”, HP put a giant “GOING OUT
OF BUSINESS! EVERYTHING MUST GO!”
sign in its store window.
Predictably (to all other than HP,
apparently), this wacky move has spooked
the enterprise customers HP intends to serve
with more products, services and devotion.
Ray Barnard, chief information officer for
Fluor Corp., told the Wall Street Journal that
his company, which normally spends $25
million per year on hardware and software,
has put on hold its plans to buy new high-end
computers from HP, because “It appears they
are lost right now” (http://online.wsj.com/
article/SB1000142405311190389590457
6544822297017068.html). Frank Purdue,
vice chancellor for information services at
Purdue University Calumet, told the paper
that he has to “reassess his tablet plans”
and was unsure how to proceed on other
fronts with HP. It’s not even worth going
into the circus around the death, rebirth,
re-death and persistent purgatorial state of
HP’s Android-based TouchPad tablets.
The US National Library of Medicine
(http://www.nlm.nih.gov) defines
psychosis as “a loss of contact with reality,
usually including false beliefs about what
is taking place or who one is (delusions)
and seeing or hearing things that aren’t
there (hallucinations)”. There is no better
characterization of HP today, and for the
last 12 years or more.
Back at the turn of the Millennium,
when IBM announced its love affair with
Linux, I wrote this in Linux Journal
(http://www.linuxjournal.com/article/4339):
“One of the things I observed about the
IBM announcement, when they essentially
declared themselves a Linux company, was
that this was clearly a company that was now
in full compliance with its own engineers.”
That’s one more reason why the sale of
IBM’s PC division to Lenovo made sense,
while HP’s rejection of its PC division did
not. IBM remains driven, to the degree it
remains sane, by its engineers. HP lost its
Way when Dave and Bill died.■
Doc Searls is Senior Editor of Linux Journal. He is also a fellow
with the Berkman Center for Internet and Society at Harvard
University and the Center for Information Technology and
Society at UC Santa Barbara.
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