Skip to main content

Monitoring Time Drift with PowerShell

· 2 min read
Mikey O'Toole

Sometimes I get a script idea put in my head that's so irritatingly pervasive that the only fix is to write the damned script. David Szpunar from the NinjaOne Users Discord made a somewhat passing comment about time drift causing issues with a remote support tool and that let to me thinking... You could probably monitor for that with a PowerShell one-liner right?

Wrong! Turns out that it's more than one line!

The Script​

This Script Requires Input
This script requires user input, whether in the form of variables, parameters or edits to the script itself before you can run it. Areas where you need to provide input will be indicated with:
### Inline Comments
and / or
'<MARKED STRINGS>'
Parameters will be indicated before the script block.
This Script Was Updated

This script was updated after being published, if you're using it please compare the version you have with the version available here.

This script was last updated on 2023/03/17.

Test-TimeDrift.ps1
loading...

Using The Script​

We tested this as a "Script Result Condition" in NinjaOne set to trigger the monitor if a machine's time drifts by more than 10 seconds from uk.pool.ntp.org (the UK's NTP pool) and it worked like a charm. The script is pretty self-explanatory but here's a quick rundown of what it does:

  1. It uses a configurable NTP or SNTP server to get the "reference" time. (Parameter -ReferenceServer)
  2. It uses the w32tm executable to conduct a number of skew checks against that reference server (Parameter -NumberOfSamples)
  3. It averages the samples and compares the result to the threshold (Parameter -AllowedTimeDrift)
  4. Optionally you can force a resync if the time drift is greater than the threshold (Parameter -ForceResync)

If the average time drift is greater than the threshold, the script returns a non-zero exit code and the monitor triggers. If the w32tm command errors (non existent server, network down etc) the script returns a non-zero exit code and the monitor triggers.

Credits​

This script borrows ideas and the approach and a little code from the excellent blog of Kevin Holman.

The formidable Chris Taylor helped with a cool suggestion to suppress empty lines in the output and his site is well worth a visit.