Dimitri's Wanderings

Jobs in Powershell

 
  • Your Name
  • May 18, 2015

This post serves more as a reference that an introduction to Powershell Jobs.

  • Cmdlets are: Get-Job, Receive-Job, Remove-Job, Resume-Job, Start-Job, Stop-Job , Suspend-Job and Wait-Job but other commands have -AsJob parameters (Get-WMIObject, Invoke-Command, CDXML snippets)
  • Help can be found in the following topics:
    • about_Jobs
    • about_Job_Details
    • about_Remote_Jobs
    • about_Scheduled_Jobs
    • about_Scheduled_Jobs_Advanced
    • about_Scheduled_Jobs_Basics
    • about_Scheduled_Jobs_Troubleshooting
  • Suspend-Job and Resume-Job are only available with workflows
  • Receive-Job deletes the data it sends to you except if you use -Keep as a parameter
  • PSJobTypeName can be
    • BackgroundJob (regular Start-Job),
    • WMIJob (Get-WmiObject -AsJob),
    • CimJob (use CDXML files, not Get-CimInstance),
    • PSScheduledJob (Register-ScheduledJob)
    • PSWorkflowJob (nameofmyworkflow -AsJob)
  • As a job is run in another Windows Powershell process than yours, you cannot use it with cmdlets such as Register-WMIEvent
  • Start-Job runs the command locally (but that command may perform remote connections), whereas Invoke-Command runs the command remotely and you get the response back.
  • If you use parameter(s), you must use ArgumentList to pass them around as jobs are run in separate Powershell instances and processes (unsecapp for Get-WMIObject, wsmprovhost for Invoke-Command)
  • Sessions (via Enter-PSSession or New-PSSession) are a way to maintain that remote connection when you have multiple script blocks to run on a target machine
  • ScheduledTasks is a CDXML (WMI Wrapper) module about the TaskScheduler, whereas PSScheduledJob manages the Powershell Scheduled Jobs which are… tasks found under \Microsoft\Windows\Powershell\ScheduledJobs
  • ScheduledJobs are primarily maintained with Register-ScheduledJob, but to work with result you must import explicitly the module and you can only see the jobs that you create/manage in your context whose results are stored in %AppData%\Local\Microsoft\Windows\Powershell\ScheduledJobs\<JobName>\Output
  • If you run jobs inside workflows, you lose the result because they are still run in an external process to yours
  • Some snippets: ``` 
    # Simple
  Start-Job -ScriptBlock { ... some action ...} -Name MySupremeJob
  Get-Job -Name MySupremeJob | select PSBeginTime, PSEndTime, @{Name='Duration';Expression={$_.PSEndTime-$_.PSBeginTime}}
  # with parameter
  Start-Job -Scriptblock {param([string]$data) Get-Service -Name $data} -ArgumentList $data
    
  #WMI Method
  $stuckjava = Get-WMIObject -Class Win32_Process -Filter "Name='javaw.exe'"
  Invoke-WmiMethod -InputObject $stuckjava -Name Terminate -AsJob
  # ScheduledJOb
  $everyday = New-JobTrigger -Daily -At "23:59"
  $god=New-ScheduledOption -RunElevated
  Register-ScheduledJob -Name RebootMe -ScritpBlock {Restart-Computer} -Trigger $everyday -ScheduledJobOption $god
  #workflows
  workflow donothing { Start-Sleep -Seconds 60; Suspend-Workflow; Write-Host "Waking up myself" } #auto-suspend
  workflow stilldonothing { Start-Sleep -Seconds 60; Checkpoint-Workflow; Write-Host "Waked up" } #suspend the job from elsewhere
  #Remote Sessions launching jobs
  $faraway = New-PSSession -ComputerName mydistantpc
  Invoke-Command -Session $faraway -ScriptBlock {Start-Job -Name WhichSvc -Scriptblock { Get-Service } }
  Invoke-Command -Session $faraway -ScriptBlock {Receive-Job -Name WhichSvc -Keep }
  Invoke-Command -Session $faraway -ScriptBlock {Get-Job | Remove-Job }
  $faraway | Remove-PSSession
    
    
  ```
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