Hi. Thanks for answering. Le 2015-09-23 17:34, Dominique Ramaekers a écrit :> 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 correctionNope. This is not installed on my system.> ntpd: > Continuously adjusts time. The deamon also calculates the drift to > anticipate differences. > I use this one and works perfectly.This is installed (package ntp, Debian Jessie) and runs (I see /usr/sbin/ntpd in `ps aux`). But after more than 24h, the 2'17 gap between hwclock and date has not reduced a bit. I guess this is not the place for me to debug my ntp issues, apart maybe from what could be related to the virtualization itself. I understood from my readings (can't remember where precisely) that the fact that ntp wouldn't work was "normal", but if it is not, maybe trying to have it working is the way to go, rather than searching for a way to automatize guest-set-time. -- Jérôme
Bill Kenworthy
2015-Sep-23 21:32 UTC
Re: [libvirt-users] Time syncing after VM suspend/resume
Look into the "panic" option to ntpd - once the gap gets to big (such as when the VM is suspended for a few hours) it goes into freewheel and doesn't sync - its in the ntp docs. ntpd doesn't work well (you get ages where a machine is way out of date, or fails to sync ever. I run either chrony (same problem) or ntpd and run a script on startup to restart guest ntp/chrony from the host via ssh. I don't think serious users suspend vm's much or this would have been fixed long ago. BillK On 23/09/15 23:44, Jérôme wrote:> Hi. > > Thanks for answering. > > Le 2015-09-23 17:34, Dominique Ramaekers a écrit : > >> 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 > > Nope. This is not installed on my system. > >> ntpd: >> Continuously adjusts time. The deamon also calculates the drift to >> anticipate differences. >> I use this one and works perfectly. > > This is installed (package ntp, Debian Jessie) and runs (I see > /usr/sbin/ntpd in `ps aux`). But after more than 24h, the 2'17 gap > between hwclock and date has not reduced a bit. > > I guess this is not the place for me to debug my ntp issues, apart maybe > from what could be related to the virtualization itself. > > I understood from my readings (can't remember where precisely) that the > fact that ntp wouldn't work was "normal", but if it is not, maybe trying > to have it working is the way to go, rather than searching for a way to > automatize guest-set-time. >
Le Thu, 24 Sep 2015 05:32:45 +0800, Bill Kenworthy <billk@iinet.net.au> a écrit :> Look into the "panic" option to ntpd - once the gap gets to big (such > as when the VM is suspended for a few hours) it goes into freewheel > and doesn't sync - its in the ntp docs.My use case is when rebooting the host (after a kernel update, for instance). The gap is about 2 minutes.> ntpd doesn't work well (you get ages where a machine is way out of > date, or fails to sync ever. I run either chrony (same problem) or > ntpd and run a script on startup to restart guest ntp/chrony from the > host via ssh.The guest-set-time command from the host works as well (but requires guest agent). I just don't know how to launch it automatically on guest resume.> I don't think serious users suspend vm's much or this would have been > fixed long ago.Interesting answer. I figured that while interrupting the host for a few minutes, suspending the guest could be a nicer option. I may be wrong. Anyway, the host shall not be rebooted that often, and I think if I don't find any satisfying answer, I may choose guest shutdown instead of suspend. In practice, my guests will likely have the same OS version, therefore the same updates and the same reboot needs. There's no point suspending a guest when rebooting the host if the guest must be rebooted anyway. -- Jérôme