Sync clock with Google

Aug 04

ErinFLOSS, Tipjar , No Comments

If the Linux VM was running at the time the host OS (Windows) hibernated then the clock in the guest VM will be left at the time of hibernation. If NTP is configured then the clock should resync gradually but most systems do not apply a big chunk of time correction by default.

If the Linux VM was configured with a VPN that implements a system-wide configuration then the DNS resolution might be unable to resolve the NTP server since the DNS of the VPN session will be unavailable. The alternate and work-around presented hinges on two things:

  • The guest VM has internet access at the time it was resumed.
  • The google.com domain name is already resolved and cached.

   sync-clock() {
     echo Current time before sync: `date`
     echo Current time after sync : `sudo date -s "$(wget -qSO- --max-redirect=0 google.com 2>&1 \ 
       | grep Date: | cut -d' ' -f5-8)Z"`
    }

The work-around uses the time in the google headers to provide an anchor for the correction.  This is provided as a bash function to provide user feedback if a correction was done.

Snippet execution

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