[libvirt-users] Time syncing after VM suspend/resume

[Dominique Ramaekers]

> -----Oorspronkelijk bericht-----
> Van: libvirt-users-bounces at redhat.com [mailto:libvirt-users-
> bounces at redhat.com] Namens Jérôme
> Verzonden: woensdag 23 september 2015 15:03
> Aan: libvirt-users at redhat.com
> Onderwerp: [libvirt-users] Time syncing after VM suspend/resume
> 
> Hi all.
> 
> When resuming guest after suspend, the time is wrong (because the guest
> doesn't know it has been suspended).
> 
> Apparently, ntp running on the guest doesn't solve this. At least on Linux
> system. I read it works on Windows guests. I don't understand why, so I'd
> appreciate a link to an explanation, but I understand it is out of scope for this
> list.

Linux has two methods to use ntp:

ntpdate:
It will run once at boot time to sync time. (This is probably installed on your system)
It will not run after suspend and resume... => no correction

ntpd:
Continuously adjusts time. The deamon also calculates the drift to anticipate differences.
I use this one and works perfectly.

> 
> The HW clock is correct and the guest agent is setup to use kvm-clock.
> 
> Using the guest-set-time command does set the clock on the guest according to
> the host. But this is not triggered automatically on resume.
> 
> I found discussions about this, even a patch proposal to call guest-set-time on
> resume, but all of this is one year old and I can't find any newer information.
> 
> http://serverfault.com/questions/334698/how-to-keep-time-on-resumed-kvm-
> guest-with-libvirt
> https://www.redhat.com/archives/libvirt-users/2014-October/msg00009.html
> https://www.redhat.com/archives/libvir-list/2014-February/msg00520.html
> 
> Is there any fresher information I have missed ?
> 
> Thanks.
> 
> --
> Jérôme
> 
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