Powershell – Windows Server notify when installing updates finished

On TechNet a lot of script exist for that, to query for the reboot required. There is one from a MSFT's employee. You can add the Restart-Computer cmdlet in the script as needed to fit your need.

See that blog post, that explain the script. Determine Pending Reboot Status—PowerShell Style! Part 1 Determine Pending Reboot Status—PowerShell Style! Part 2

Link to the script. Get-PendingReboot - Query Computer(s) For Pending Reboot State

Function Get-PendingReboot
{
<#
.SYNOPSIS
    Gets the pending reboot status on a local or remote computer.

.DESCRIPTION
    This function will query the registry on a local or remote computer and determine if the
    system is pending a reboot, from Microsoft updates, Configuration Manager Client SDK, Pending Computer 
    Rename, Domain Join or Pending File Rename Operations. For Windows 2008+ the function will query the 
    CBS registry key as another factor in determining pending reboot state.  "PendingFileRenameOperations" 
    and "Auto Update\RebootRequired" are observed as being consistant across Windows Server 2003 & 2008.

    CBServicing = Component Based Servicing (Windows 2008+)
    WindowsUpdate = Windows Update / Auto Update (Windows 2003+)
    CCMClientSDK = SCCM 2012 Clients only (DetermineIfRebootPending method) otherwise $null value
    PendComputerRename = Detects either a computer rename or domain join operation (Windows 2003+)
    PendFileRename = PendingFileRenameOperations (Windows 2003+)
    PendFileRenVal = PendingFilerenameOperations registry value; used to filter if need be, some Anti-
                     Virus leverage this key for def/dat removal, giving a false positive PendingReboot

.PARAMETER ComputerName
    A single Computer or an array of computer names.  The default is localhost ($env:COMPUTERNAME).

.PARAMETER ErrorLog
    A single path to send error data to a log file.

.EXAMPLE
    PS C:\> Get-PendingReboot -ComputerName (Get-Content C:\ServerList.txt) | Format-Table -AutoSize

    Computer CBServicing WindowsUpdate CCMClientSDK PendFileRename PendFileRenVal RebootPending
    -------- ----------- ------------- ------------ -------------- -------------- -------------
    DC01           False         False                       False                        False
    DC02           False         False                       False                        False
    FS01           False         False                       False                        False

    This example will capture the contents of C:\ServerList.txt and query the pending reboot
    information from the systems contained in the file and display the output in a table. The
    null values are by design, since these systems do not have the SCCM 2012 client installed,
    nor was the PendingFileRenameOperations value populated.

.EXAMPLE
    PS C:\> Get-PendingReboot

    Computer           : WKS01
    CBServicing        : False
    WindowsUpdate      : True
    CCMClient          : False
    PendComputerRename : False
    PendFileRename     : False
    PendFileRenVal     : 
    RebootPending      : True

    This example will query the local machine for pending reboot information.

.EXAMPLE
    PS C:\> $Servers = Get-Content C:\Servers.txt
    PS C:\> Get-PendingReboot -Computer $Servers | Export-Csv C:\PendingRebootReport.csv -NoTypeInformation

    This example will create a report that contains pending reboot information.

.LINK
    Component-Based Servicing:
    http://technet.microsoft.com/en-us/library/cc756291(v=WS.10).aspx

    PendingFileRename/Auto Update:
    http://support.microsoft.com/kb/2723674
    http://technet.microsoft.com/en-us/library/cc960241.aspx
    http://blogs.msdn.com/b/hansr/archive/2006/02/17/patchreboot.aspx

    SCCM 2012/CCM_ClientSDK:
    http://msdn.microsoft.com/en-us/library/jj902723.aspx

.NOTES
    Author:  Brian Wilhite
    Email:   bcwilhite (at) live.com
    Date:    29AUG2012
    PSVer:   2.0/3.0/4.0/5.0
    Updated: 27JUL2015
    UpdNote: Added Domain Join detection to PendComputerRename, does not detect Workgroup Join/Change
             Fixed Bug where a computer rename was not detected in 2008 R2 and above if a domain join occurred at the same time.
             Fixed Bug where the CBServicing wasn't detected on Windows 10 and/or Windows Server Technical Preview (2016)
             Added CCMClient property - Used with SCCM 2012 Clients only
             Added ValueFromPipelineByPropertyName=$true to the ComputerName Parameter
             Removed $Data variable from the PSObject - it is not needed
             Bug with the way CCMClientSDK returned null value if it was false
             Removed unneeded variables
             Added PendFileRenVal - Contents of the PendingFileRenameOperations Reg Entry
             Removed .Net Registry connection, replaced with WMI StdRegProv
             Added ComputerPendingRename
#>

[CmdletBinding()]
param(
    [Parameter(Position=0,ValueFromPipeline=$true,ValueFromPipelineByPropertyName=$true)]
    [Alias("CN","Computer")]
    [String[]]$ComputerName="$env:COMPUTERNAME",
    [String]$ErrorLog
    )

Begin {  }## End Begin Script Block
Process {
  Foreach ($Computer in $ComputerName) {
    Try {
        ## Setting pending values to false to cut down on the number of else statements
        $CompPendRen,$PendFileRename,$Pending,$SCCM = $false,$false,$false,$false

        ## Setting CBSRebootPend to null since not all versions of Windows has this value
        $CBSRebootPend = $null

        ## Querying WMI for build version
        $WMI_OS = Get-WmiObject -Class Win32_OperatingSystem -Property BuildNumber, CSName -ComputerName $Computer -ErrorAction Stop

        ## Making registry connection to the local/remote computer
        $HKLM = [UInt32] "0x80000002"
        $WMI_Reg = [WMIClass] "\\$Computer\root\default:StdRegProv"

        ## If Vista/2008 & Above query the CBS Reg Key
        If ([Int32]$WMI_OS.BuildNumber -ge 6001) {
            $RegSubKeysCBS = $WMI_Reg.EnumKey($HKLM,"SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing\")
            $CBSRebootPend = $RegSubKeysCBS.sNames -contains "RebootPending"        
        }

        ## Query WUAU from the registry
        $RegWUAURebootReq = $WMI_Reg.EnumKey($HKLM,"SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update\")
        $WUAURebootReq = $RegWUAURebootReq.sNames -contains "RebootRequired"

        ## Query PendingFileRenameOperations from the registry
        $RegSubKeySM = $WMI_Reg.GetMultiStringValue($HKLM,"SYSTEM\CurrentControlSet\Control\Session Manager\","PendingFileRenameOperations")
        $RegValuePFRO = $RegSubKeySM.sValue

        ## Query JoinDomain key from the registry - These keys are present if pending a reboot from a domain join operation
        $Netlogon = $WMI_Reg.EnumKey($HKLM,"SYSTEM\CurrentControlSet\Services\Netlogon").sNames
        $PendDomJoin = ($Netlogon -contains 'JoinDomain') -or ($Netlogon -contains 'AvoidSpnSet')

        ## Query ComputerName and ActiveComputerName from the registry
        $ActCompNm = $WMI_Reg.GetStringValue($HKLM,"SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName\","ComputerName")            
        $CompNm = $WMI_Reg.GetStringValue($HKLM,"SYSTEM\CurrentControlSet\Control\ComputerName\ComputerName\","ComputerName")

        If (($ActCompNm -ne $CompNm) -or $PendDomJoin) {
            $CompPendRen = $true
        }

        ## If PendingFileRenameOperations has a value set $RegValuePFRO variable to $true
        If ($RegValuePFRO) {
            $PendFileRename = $true
        }

        ## Determine SCCM 2012 Client Reboot Pending Status
        ## To avoid nested 'if' statements and unneeded WMI calls to determine if the CCM_ClientUtilities class exist, setting EA = 0
        $CCMClientSDK = $null
        $CCMSplat = @{
            NameSpace='ROOT\ccm\ClientSDK'
            Class='CCM_ClientUtilities'
            Name='DetermineIfRebootPending'
            ComputerName=$Computer
            ErrorAction='Stop'
        }
        ## Try CCMClientSDK
        Try {
            $CCMClientSDK = Invoke-WmiMethod @CCMSplat
        } Catch [System.UnauthorizedAccessException] {
            $CcmStatus = Get-Service -Name CcmExec -ComputerName $Computer -ErrorAction SilentlyContinue
            If ($CcmStatus.Status -ne 'Running') {
                Write-Warning "$Computer`: Error - CcmExec service is not running."
                $CCMClientSDK = $null
            }
        } Catch {
            $CCMClientSDK = $null
        }

        If ($CCMClientSDK) {
            If ($CCMClientSDK.ReturnValue -ne 0) {
                Write-Warning "Error: DetermineIfRebootPending returned error code $($CCMClientSDK.ReturnValue)"          
            }
            If ($CCMClientSDK.IsHardRebootPending -or $CCMClientSDK.RebootPending) {
                $SCCM = $true
            }
        }

        Else {
            $SCCM = $null
        }

        ## Creating Custom PSObject and Select-Object Splat
        $SelectSplat = @{
            Property=(
                'Computer',
                'CBServicing',
                'WindowsUpdate',
                'CCMClientSDK',
                'PendComputerRename',
                'PendFileRename',
                'PendFileRenVal',
                'RebootPending'
            )}
        New-Object -TypeName PSObject -Property @{
            Computer=$WMI_OS.CSName
            CBServicing=$CBSRebootPend
            WindowsUpdate=$WUAURebootReq
            CCMClientSDK=$SCCM
            PendComputerRename=$CompPendRen
            PendFileRename=$PendFileRename
            PendFileRenVal=$RegValuePFRO
            RebootPending=($CompPendRen -or $CBSRebootPend -or $WUAURebootReq -or $SCCM -or $PendFileRename)
        } | Select-Object @SelectSplat

    } Catch {
        Write-Warning "$Computer`: $_"
        ## If $ErrorLog, log the file to a user specified location/path
        If ($ErrorLog) {
            Out-File -InputObject "$Computer`,$_" -FilePath $ErrorLog -Append
        }               
    }           
  }## End Foreach ($Computer in $ComputerName)          
}## End Process

End {  }## End End

}## End Function Get-PendingReboot