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"Corporate" Blog of Daniele Muscetta, Premier Field Engineer.

Get-WmiCustom (aka: Get-WMIObject with timeout!)

I make heavy use of WMI.

But when using it to gather information from customer’s machines for assessments, I sometimes find the occasional broken WMI repository. There are a number of ways in which WMI can become corrupted and return weird results. Most of the times you would just get errors, such as “Class not registered” or “provider load failure”. I can handle those errors from within scripts.

But there are some, more subtle – and annoying – ways in which the WMI repository can get corrupted. the situations I am talking about are the ones when WMI will accept your query… will say it is executing it… but it will never actually return any error, and just stay stuck performing your query forever. Until your client application decides to time out. Which in some cases does not happen.

Now that was my issue – when my assessment script (which was using the handy Powershell Get-WmiObject cmdlet) would hit one of those machines… the whole script would hang forever and never finish its job. Ok, sure, the solution to this would be actually FIXING the WMI repository and then try again. But remember I am talking of an assessment: if the information I am getting is just one piece of a bigger puzzle, and I don’t necessarily care about it and can continue without that information – I want to be able to do it, to skip that info, maybe the whole section, report an error saying I am not able to get that information, and continue to get the remaining info. I can still fix the issue on the machine afterward AND then run the assessment script again, but in the first place I just want to get a picture of how the system looks like. With the good and with the bad things. Especially, I do want to take that whole picture – not just a piece of it.

Unfortunately, the Get-WmiObject cmdlet does not let you specify a timeout. Therefore I cooked my own function which has a compatible behaviour to that of Get-WmiObject, but with an added “-timeout” parameter which can be set. I dubbed it “Get-WmiCustom”

Function Get-WmiCustom([string]$computername,[string]$namespace,[string]$class,[int]$timeout=15)
$ConnectionOptions = new-object System.Management.ConnectionOptions
$EnumerationOptions = new-object System.Management.EnumerationOptions

$timeoutseconds = new-timespan -seconds $timeout

$assembledpath = “\” + $computername + “” + $namespace
#write-host $assembledpath -foregroundcolor yellow

$Scope = new-object System.Management.ManagementScope $assembledpath, $ConnectionOptions

$querystring = “SELECT * FROM ” + $class
#write-host $querystring

$query = new-object System.Management.ObjectQuery $querystring
$searcher = new-object System.Management.ManagementObjectSearcher
$searcher.Query = $querystring
$searcher.Scope = $Scope

trap { $_ } $result = $searcher.get()

return $result

You can call it as follows, which is similar to how you would call get-WmiObject

get-wmicustom -class Win32_Service -namespace “rootcimv2″ -computername server1.domain.dom

or, of course, specifying the timeout (in seconds):

get-wmicustom -class Win32_Service -namespace “rootcimv2″ -computername server1.domain.dom –timeout 1

and obviously, since the function returns objects just like the original cmdlet, it is also possible to pipe them to other commands:

get-wmicustom -class Win32_Service -namespace “rootcimv2″ -computername server1.domain.dom –timeout 1 | Format-Table