Jobs, scheduling and remoting

Some work is slow - pinging twenty enclosure sensors, copying big backups. Background jobs run it while you carry on:

A job runs in a separate process, so it can’t see your variables. Pass values in with -ArgumentList (they arrive as $args or the job’s param()), or refer to them as $using:name.

Starting a whole process per job is heavy. Two lighter options run in threads inside your session:

• Start-ThreadJob - same commands as Start-Job, much faster to start (built into PowerShell 7).
• ForEach-Object -Parallel (PowerShell 7) - run a script block for many items at once, up to -ThrottleLimit at a time:

$sensors | ForEach-Object -Parallel {
  Test-Connection "$_.sensors.emberfall" -Count 1 -Quiet
} -ThrottleLimit 10

To run a script every night, hand it to the operating system’s scheduler:

• Windows Task Scheduler: Register-ScheduledTask with a trigger (New-ScheduledTaskTrigger -Daily -At 3am) and an action (New-ScheduledTaskAction -Execute pwsh -Argument '-File C:\Scripts\Feed.ps1').
• Linux and macOS: a cron line such as 0 3 * * * pwsh -File /opt/scripts/feed.ps1.

Scheduled scripts run without you watching, so use everything from the last two lessons: strict mode, -ErrorAction Stop with try/catch, a transcript or log, and a non-zero exit code on failure.

PowerShell remoting runs commands on other computers and sends back objects, not text:

1# Run one command on several servers at once
2Invoke-Command -ComputerName castle-01, castle-02 -ScriptBlock { Get-Service sshd }
3
4# An interactive session on a remote machine (exit with Exit-PSSession)
5Enter-PSSession -ComputerName castle-01
6
7# A reusable connection for several commands
8$session = New-PSSession -ComputerName castle-01
9Invoke-Command -Session $session { Get-Volume }

On Windows, remoting uses WinRM (Enable-PSRemoting turns it on). PowerShell 7 can also remote over SSH to Linux and macOS: Invoke-Command -HostName keeper@castle-03 { uname -a }. Results come back as deserialized objects - their properties are there, but methods that would act on the remote machine aren’t.

On Windows, CIM gets hardware and OS details from any machine: Get-CimInstance Win32_OperatingSystem -ComputerName castle-01 | Select-Object Caption, LastBootUpTime.