PowerShell and WMI Namespaces

Over on Tim Benninghoff blog – he has an interesting post:: PowerShell and WMI namespaces. With WMI, the classes and intances are organised under a hierarchal namespace starting at the appropriately named “root”.  Individual nodes can have children which can in turn have children and so on. To some degree, namespaces are just defined by a product team and there is little consistency across software products (such is life!). But where to start?

Despite what Tim says about using the GUI, MOW’s most excellent WMI Explorer script is one fantastic tool. Not only is it a really good browser, but as Tim notes, it’s written in PowerShell which is even more cool. I use this script in most of my training courses to add value!

His post then goes on to describe two methods of obtaining the namespaces within WMI. There are two small problems with his examples. In his first example he has a minor typo – this should read as follows:

gwmi -namespace "root" -class "__Namespace" | Select Name

In Tim’s post, he spelt the class with just a single underline (“_Namespace”) not two (“__Namespace”). WMI is sadly very picky!  Tim’s other method works fine and as he says produces the same output as his first (well once corrected!). On my system, this produces the following output:

PSH [C:\foo]: gwmi -namespace "root" -class "__Namespace" | Select Name

Name
----
subscription
DEFAULT
MicrosoftDfs
CIMV2
Cli
nap
MicrosoftIISv2
SECURITY
RSOP
MicrosoftDNS
WebAdministration
WMI
directory
Policy
virtualization
Hardware
ServiceModel
MSAPPS12
Microsoft
aspnet

The second point is that his two methods just produce a list of namespaces under the root. Since each node in the namespace can have children, his two methods do not list all the namespaces in which you can find classes. This, IMHO, is once case where the GUI is a better tool – visualising the hierarchy in a tree control is a whole lot easier than trying to do it from the command line. And you get the names spaces in alphabetical order (although you could do pipe the output above to Sort-Object easily enough). On my workstation I see a number of subsidiary namespaces below root as you can see here:

 

WMI Namespaces are a good thing to understand, since many of the classes you might want to access using Get-WMIObject (et al) rely on the –NameSpace paramater (and the appropriate namespace name!).

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