Use PowerShell to test if a Windows server is pending a reboot

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Adam Bertram

Adam Bertram is a 20-year IT veteran, Microsoft MVP, blogger, and trainer.

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To prevent service interruptions, you have to schedule Windows server reboots. With the help of PowerShell, you can check whether a particular Windows server requires a reboot or not.

Unfortunately, we can't always keep our servers up 24/7. In Windowsland especially, a reboot now and then is required. There are many different reasons a server may need a reboot, like software that needs to modify something currently running, a locked file that refuses to let go without a boot, or perhaps a service that can only apply a change at boot time.

The solution to a needed reboot is simple: reboot it! But it's not always that simple. Servers are serving users, and users don't like it when their services go down at any time. Also, if you manage a lot of servers, you may want to schedule a maintenance window to reboot them all at once rather than as needed. In such a case, you need to know which ones need rebooting and which ones don't. How to determine that isn't too clear on a Windows server.

There is no one area to look at to tell whether a Windows server needs a reboot. The flags are spread out amongst a few different registry keys. Luckily, we can use a PowerShell script to query these registry values and return a simple True or False to indicate if one or more servers need a three-finger salute.

Before we get to the PowerShell, you need to understand where to look. There are three (or more I'm not aware of) registry values you should check to see whether a reboot is needed or not.

• The RebootPending value at

  HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing

• The RebootRequired value at

  HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update

• The PendingFileRenameOperations value at

  HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager

Knowing these registry values, we then create the PowerShell code to check for them on a remote server. We'll do this over PowerShell Remoting, so I'm assuming it is available on your servers.

The server is pending a reboot if the RebootPending and RebootRequired values exist. Let's build some code to check for these registry values' existence. I'm getting a little fancy here by creating an array of hash tables. I'm doing this because it makes it easier to add more checks if one day you find out you need to check other registry values. Using an array like this will allow me to loop over each test quickly.

Also, notice below I'm ignoring errors because if it throws an error, I'm going to assume the value does not exist.

$pendingRebootTests = @(
    @{
        Name = 'RebootPending'
        Test = { Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing'  Name 'RebootPending' -ErrorAction Ignore }
        TestType = 'ValueExists'
    }
    @{
        Name = 'RebootRequired'
        Test = { Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update'  Name 'RebootRequired' -ErrorAction Ignore }
        TestType = 'ValueExists'
    }
    @{
        Name = 'PendingFileRenameOperations'
        Test = { Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager' -Name 'PendingFileRenameOperations' -ErrorAction Ignore }
        TestType = 'NonNullValue'
    }
)

Now that we have the code built to run the tests, let's create a PowerShell Remoting session and run these scriptblocks on a server.

## Create a PowerShell Remoting session
$session = New-PSSession -Computer SRV1
foreach ($test in $pendingRebootTests) {
    Invoke-Command -Session $session -ScriptBlock $test.Test
}

This will run the code on all the servers but won't return a simple True or False as we need. To do this, we need to add some if/then logic to it. Since only two of the tests need to return True or False if the registry key exists or not, we'll use the TestType key in each hash table to make that distinction.

$session = New-PSSession -Computer SRV1
foreach ($test in $pendingRebootTests) {
    $result = Invoke-Command -Session $session -ScriptBlock $test.Test
    if ($test.TestType -eq 'ValueExists' -and $result) {
        $true
    } elseif ($test.TestType -eq 'NonNullValue' -and $result -and $result.($test.Name)) {
        $true
    } else {
        $false
    }
}
$session | Remove-PSSession

Pending reboot test

At this point, we can get an output from this server with the results of each of the checks we've done. This function is also built to expand upon by adding additional servers if need be.