Comprehensive Guide to WMI (1).key

Guide to WMI
The Comprehensive
Guide to WMI
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What is WMI?
WMI stands for Windows Management Instrumentation. WMI’s
WMI’s purpose is
purpose is similar to that of SNMP (Simple Network Management
similar to that of
Protocol): to enable the querying and control of management
SNMP: to enable the
information in an enterprise - but it has a significantly different
querying and control
architecture under the covers. Compared to SNMP, WMI provides a
of management
higher-level representation of systems, in that it supports
information in an
properties, events and methods on top of classes of objects, along
with a more powerful query language than SNMP supports. Of
course, this also means it’s a bit more complex to use, and has more
overhead on the systems. It has been available in Windows since
way back in the Windows 95 and Windows NT era.
WMI is the Microsoft implementation of Web-Based Enterprise
Management (WBEM), which is an industry initiative for a standard
technology for accessing management information in an enterprise
environment. WMI uses the Common Information Model (CIM)
industry standard. And as happens with so many implementations
of standards – it is not at all interoperable with any other version of
the standard.
In other words, WMI is an implementation of ‘standards based’
management, which only works on and with Windows.
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However, as WMI has been Microsoft’s main (but not exclusive!
More on that later) focus for exposing information about system
performance and configuration, it is the preferred way of collecting
information from Windows systems for many monitoring systems.
(Windows systems can run SNMP, but compared to the built-in WMI
support, the built-in SNMP agent provides very little information.)
See it in Action! Querying WMI using WBEMTest
There are a variety of ways of querying WMI. We’ll discuss these
later, but for now, we’ll use WBEMtest, which is a Microsoft tool for
testing and using WMI. It has the advantage of being included with
WBEMTest can connect to the local computer and to remote
computers – but connecting to the local computer avoids any of the
many possible issues that can interfere with remote WMI. (Again –
more on that later.)
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Run WBEMTest (from the Start menu), and you’ll see a simple
Click Connect, and then Connect again on the next form to display.
The defaults are appropriate for connecting to the local system.
Now that we are connected, the form will have the buttons enabled.
Clicking the “Query” button will allow us to enter a WQL (Windows
Query Language) query, which is how WMI data is queried.
Enter the query:
Select * from win32_computerSystem
and click apply:
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A window should return, with one line, listing the name of your
Double click the result line, and a new window will open, listing all
the properties (and methods) of the returned object.
There will be properties for the Manufacturer, the BootUpState,
Domain, TotalPhysicalMemory, and so on.
In this case, we queried the class Win32_ComputerSystem, in the
Namespace cimv2. The namespace was specified when we
connected – cimv2 is the default namespace, and where almost all
Windows performance and configuration data is found. Some
specialized software, with different security requirements, may use a
different namespace.
Above, we used a very simple query to show information about the
computer itself - but you can also query information for things with
multiple occurrences, and use conditions to refine the results.
For example:
select * from Win32_NetworkAdapter where AdapterType like
will return information about ethernet network adapters, but not
wireless or ATM adapaters.
The full definition of WQL options are available on this MSDN
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WQL is similar to standard SQL (Structured Query Language), used
by many popular databases. If you’re familiar with SQL, the
comparison table below may help:
Individual items
Containers of columns and
Containers of tables
Program code that
functions on data
What can you query with WMI?
The answer is easy: almost anything. WMI has classes for almost
anything you may want to know about a computer – hardware
information, performance information, software information – and in
many cases there are classes added for installed software, so you
can even monitor things like Exchange mailboxes. The hard thing is
in knowing how to get the information.
Unlike SNMP, WMI does not have the concept of a published MIB
(Management Information Base, detailing all the SNMP queries that
are supported). Some classes are well documented, but many are
not documented at all, or only mentioned in passing on occasional
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WMI information is in a hierarchical tree under namespaces. Some
of the namespaces have hundreds of classes in them and each class
often has dozens of properties. This can make finding the
namespace and class that has the information you are looking for
the hardest part of using WMI.
A good place to start for finding the right WMI classes is this MSDN
page. While this is a great resource for WMI information, it does not
mean that the information you want will be easy to find. For instance
– to determine that a system’s BootUpState (for example “Normal
Boot”, as opposed to "Fail-safe boot") can be found in the
Win32_computerSystem name class we used above, you’d have to
navigate to the WMI providers page, down into the CIMWin32
section, then to Win32 Provider, then Operating System Classes,
and finally to the Win32_ComputerSystem page, for a listing of all
the properties and methods of that class. Often it’s easier to use
your favorite search engine to search for what you want, by
searching for a phrase like WMI boot state. (Ironically, the first
Google result for that search is the Win32_computerSystem class
page, but that result doesn’t show on the first page of Bing…)
There are, of course, things that are not exposed via WMI. Some
aspects of Exchange can only be monitored via powershell scripts
(such as Get-MailboxDatabaseCopyStatus – there is no equivalent
WMI class.) The core OS is well instrumented via WMI, but the extra
packages (Exchange, SQL Server, Clustering, etc) seem as if they
sometimes added on WMI support as an afterthought, and forgot to
expose some important things. In general, though, most things you
would want to query are exposed by WMI.
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Why would you use WMI? Because SCRIPTS!
If you are monitoring your Windows servers with an automated
platform like LogicMonitor, most likely it is using WMI to query a
good chunk of the information it is collecting about your servers.
The tool will have all the WMI discovery, queries and filtering taken
care of for you. Nonetheless, understanding WMI is great if you
want to extend the monitoring.
But WMI is also great for system administration apart from
monitoring. Being able to query your own computer’s boot-state is
nice – but not terribly useful. Being able to run a script that uses
WMI to query all the computers on your network, to see if any have
booted into fail-safe mode and need attention, and being able to
update drivers on those that do – well, that is more interesting.
WMI is easy to call from programming and scripting languages,
which means it’s easy to perform queries and reports on all the
computers you are responsible for.
Below is a simple script using VBscript:
' Lines
' set computer to current computer
strComputer = "."
' connect to WMI in the namespace called “CIMV2”
Set objWMIService = GetObject("winmgmts:\\" & strComputer &
' run the WMI query
Set colItems
'Loops thru each BIOS Object and gets the value and shows
the value
For Each objItem in colItems
Wscript.Echo "SerialNumber: " & objItem.SerialNumber
' end
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If you save this file (make sure you use ANSI encoding) with a .vbs
extension, and run it, you will get a dialog pop up showing the serial
number of the BIOS.
You can achieve similar results using Powershell commands to
access WMI:
Get-WmiObject win32_BIOS | Select SerialNumber
There are also tools such as “Scriptomatic” which not only help in
exploring WMI namespaces and the WMI classes within those
Namespaces - it also can create script/code in various languages to
extract the WMI information.
There are also many sites with pre-built WMI scripts, such as this
one that uses WMI to perform an inventory report on all computers
found in the AD tree.
WMI to remote computers
There are several requirements to making WMI work on remote
• Network access for WMI (which uses DCOM) needs to be allowed
by any firewalls on or between the computers.
• User access and credentials are needed for remote WMI access.
Firewalls and WMI:
Because WMI uses DCOM (Distributed Component Object Model)
by default to communicate between computers, it doesn’t use a
single port – so it’s not easy to allow through firewalls. DCOM uses
TCP port 135 to initiate connections, but then dynamically chosen
ports are used to actually transfer data.
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The actual port numbers are different depending on the version of
Windows. On older versions of Windows (i.e. Windows 2000,
Windows XP and Windows Server 2003) the dynamically chosen
ports are in the range of 1025 to 5000. On newer versions of
Windows (Vista, Windows Server 2008 and later) ports are in the
range of 49152 to 65535. See this Microsoft article for details. This
makes it hard to run WMI through firewalls without opening up a
wide range of ports.
The Microsoft built in firewall can deal with the dynamic ports, but
by default will block WMI. To enable remote WMI access while using
the Windows Firewall:
• You can use a netsh firewall command at the command prompt to
allow for remote administration. The following command enables
this feature:
netsh firewall set service RemoteAdmin enable or (depending on
your version of Windows)
netsh advfirewall firewall set rule group="windows management
instrumentation (wmi)" new enable=yes
• You can use either the Group Policy editor (Gpedit.msc) or a
script to enable the Windows Firewall: Allow remote administration
exception. To use the Group Policy editor, use the following steps in
the Group Policy editor to enable "Allow Remote Administration":
a. Under the Local Computer Policy heading, double
click Computer Configuration.
b. Double-click Administrative Templates, Network, Network
Connections, and then Windows Firewall.
c. If the computer is in the domain, then double-click Domain
Profile; otherwise, double-click Standard Profile.
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d. Click Windows Firewall: Allow remote administration
e. On the Action menu, select Properties.
f. Click Enable, and then click OK.
There are other approaches to making WMI more firewall friendly –
such as limiting the range of ports that DCOM will use via
dcomcnfg, or configuring the WMI service to run in standalone
mode with a fixed port via WinMgmt.exe /StandAloneHost - but, as
in most systems administration tasks, the less things that are
changed from default, the less problems you are likely to run into,
so we won’t explore these methods.
WMI User Credentials:
Connecting to the WMI service on the local system avoids any issues
with user credentials (indeed, it refuses to use them), and will always
connect with the account of the user running the WMI query. When
connecting to a remote server, however, you can use different
credentials to connect.
The simplest case is where the account used to connect to WMI on
the remote computer is a domain account in the Administrators
group (not necessarily a domain Admin.) Because of User Account
Control, the account running the WMI query must be in the
Administrators group on the local computer to have the ability to
run with elevated rights. This means that the user you connect as
must be a domain account in the administrators group, on the
computer you are querying WMI on.
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If you are using an account other than your own to connect to
remote servers via scripts, or with a monitoring tool such as
LogicMonitor, it is recommended that you set “password does not
expire” on this user account – otherwise when the password expires,
it may require changing many scripts or services.
Troubleshooting WMI
WMI is great when it works, but when it doesn’t – it can be
frustrating. Generally the first step is ensuring that WMI works
locally, using WBEMTest while logged in to the computer itself. This
eliminates any firewalls and username password/domain issues.
But even then, you will sometimes run into oddities – in which case
these are some things to check.
WMI Services & Dependencies
All of the following services should be running and set to an
"Automatic" startup type for WMI monitoring to work correctly:
• DCOM Server Process Launcher
• Remote Procedure Call (RPC)
• RPC Endpoint Mapper
• Windows Management Instrumentation
And the following service(s) may be set to a "Manual" startup type:
• WMI Performance Adapter
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Weird Data from WMI
Sometimes you’ll find that while some WMI queries work fine, some
WMI data cannot be retrieved – even for objects that do in fact
exist. You may retrieve errors such as "Empty result set", or the
permission error 0x80041003 on some objects, but not others.
In this case, rebuilding the Performance Counter library may be
necessary. Why? Because .. well… Erm, the registry……. Just try it.
It does actually fix issues.
If WBEMTest works locally, but remote WMI does not – you most
likely have either a firewall issue, or are passing in incorrect user
credentials. For further WMI troubleshooting advice – see this
Microsoft page.
What next?
Well, having read this far, you’ll most likely be using WMI either in a
monitoring tool, where you may want to add in some extra classes
to get some specific information the monitoring doesn’t provide
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out-of-the-box, or you’ll be using scripting (most likely Powershell)
to manage and script systems administration tasks.
For example, you should be able to easily write a quick powershell
to get free space information on all drives on a remote computer (or
all your computers!):
get-wmiobject -class Win32_Volume -computername atl-fs-01 |
Object name,freespace,driveletter | Sort-Object name
And here’s the kind of data you get back:
The Comprehensive
Guide to WMI
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you by our team of IT experts at
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But be advised – once you dive into this world of automated
monitoring and management – there is a lot to keep up with.
For example, Microsoft is now using Windows Management
Infrastructure (with the helpfully distinguishing acronym MI), which is
backward compatible with Windows Management Interface – but is
more compliant with the current management standards; can be run
without DCOM, and is easier for software companies to write
providers for. For similar reasons, powershell is deprecating the
common Get-WMiObject Cmdlet – it has been superseded by Get
CimInstance. (But Get-CimInstance uses a different protocol by
default, which doesn’t work with 2003 servers – but can be
configured to use DCOM for backward compatibility… No one said
this was easy!)
If you always run the same level of servers everywhere, it’s less
complicated, but with a mix of older and newer operating systems
to support – the mix of tools that will work on each will require you
to expand your bag of tricks all the time.
WMI is a very powerful way to retrieve information about systems
and their performance. Knowing your way around WMI can help you
Deliver optimal
performance to
the people you
LogicMonitor’s SaaS-based
performance monitoring
platform helps top IT teams
improve the monitoring of your systems, and help you automate
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many common systems administration tasks. Indeed – an installation
across their deployment.
option on Windows 2016 is the Nano Server – which has no GUI,
and has all management performed on it remotely via WMI and
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powershell. WMI is the de facto foundation of Microsoft’s
management strategy. The more you are familiar with it, the better
systems administrator you can be. And helping you and your team
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