Deleting a saved state through WMI [Hyper-V]

I received this question from our product support team this week:

“How do you delete the saved state of a virtual machine through WMI?”

What they are refering to here is the fact that – through the Hyper-V Manager user interface – you can delete the saved state of a virtual machine that is in a saved state:

The most common reason for wanting to do this is because you have moved a virtual machine (with a saved state) to another computer – and the saved state is no longer compatible.

The problem is that there is no “delete saved state” WMI API.  The reason for this is that – at a WMI level – to delete a saved state all you need to do is to “turn off” the virtual machine.  Here is a sample script that turns off a virtual machine:

 # Function for handling WMI jobs / return values
 Function ProcessResult($result, $successString, $failureString)
 {
    #Return success if the return value is "0"
    if ($result.ReturnValue -eq 0)
       {write-host $successString} 
  
    #If the return value is not "0" or "4096" then the operation failed
    ElseIf ($result.ReturnValue -ne 4096)
       {write-host $failureString "  Error value:" $result.ReturnValue}
  
    Else
       {#Get the job object
       $job=[WMI]$result.job
  
       #Provide updates if the jobstate is "3" (starting) or "4" (running)
       while ($job.JobState -eq 3 -or $job.JobState -eq 4)
          {write-host $job.PercentComplete "% complete"
           start-sleep 1
  
           #Refresh the job object
           $job=[WMI]$result.job}
  
        #A jobstate of "7" means success
        if ($job.JobState -eq 7)
           {write-host $successString}
        Else
           {write-host $failureString
           write-host "ErrorCode:" $job.ErrorCode
           write-host "ErrorDescription" $job.ErrorDescription}
        }
 }
  
 # Prompt for the Hyper-V Server to use
 $HyperVServer = Read-Host "Specify the Hyper-V Server to use (enter '.' for the local computer)"
  
 # Prompt for the virtual machine to use
 $VMName = Read-Host "Specify the name of the virtual machine"
  
 # Get the management service
 $VMMS = gwmi -namespace root\virtualization Msvm_VirtualSystemManagementService -computername $HyperVServer
  
 # Get the virtual machine object
 $VM = gwmi MSVM_ComputerSystem -filter "ElementName='$VMName'" -namespace "root\virtualization" -computername $HyperVServer
  
 # Turn off the virtual machine
 $result = $VM.RequestStateChange(3)
  
 # Check to see that we were successful
 ProcessResult $result "The virtual machine has been turned off." "Failed to turn off the virtual machine."

If you run this on a running virtual machine, the virtual machine will be turned off.  But if you run this on a virtual machine that is in a saved state – the saved state will be deleted instead.

Cheers,
Ben

TurnOffVM.zip

Comments

• Anonymous
  July 02, 2015
  I tried to run the script but i am getting error like below, so what should i do to solve this?   You cannot call a method on a null-valued expression. At C:tempTurnOffVM.ps1:47 char:1 $result = $VM.RequestStateChange(3)

•                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• CategoryInfo          : InvalidOperation: (:) [], RuntimeException
• FullyQualifiedErrorId : InvokeMethodOnNull