[Users] Time keeping in Windows VM

[Dan Kenigsberg]

On Tue, Nov 19, 2013 at 04:36:24PM +0000, Martin Goldstone wrote:
> Hi all,
> 
> We're currently experiencing an issue in our production oVirt 3.2.2
> environment (on CentOS 6.4) with time keeping on our Windows guests. It
> seems to have appeared around the time of the recent DST change. It's taken
> us a while to get to the bottom of this as some machines were created in
> the wrong timezone, which muddied the waters a bit.
> 
> It appears that when Windows automatically updated time in the VMs, this
> new offset from UTC was not stored correctly, and the next time the host
> was shutdown and started back up, the clock was set incorrectly. We
> eventually managed to get this to be consistently reproducible:  Set the
> clock an hour ahead; power off VM; power it back on; set the clock an hour
> back (ie return it to the original time), power off and power back on;
> observe that the clock has now shifted to an hour before the original time.
> This can be observed in the vm_dynamic table on the database.
> 
> To be honest, I don't think that this an oVirt problem, as I've done some
> limited testing on another host using virt-manager/libvirt. If I edit the
> xml to set the clock offset to variable, using UTC as the basis and setting
> the adjustment to 3600 (mimicking how it would have been before the DST
> change), when I change the time in the VM back by an hour (as Windows would
> do automatically at DST change), the xml shows a new offset of -3600, so it
> seems when the clock is changed the offset it's putting in the XML is the
> offset based on the time from when the VM was started, not the offset from
> UTC.

I believe that you are seeing "Bug 956741 - When RHEL VMs are powered
off/on time is off by as much as 3 hrs when system comes back up".

http://libvirt.org/html/libvirt-libvirt.html#virConnectDomainEventRTCChangeCallback
says that utcoffset is relative to UTC. If it's not so, it's a bug
(either in the doc or in the code) so I'm copying libvir-list.

Which libvirt and qemu versions do you have?


> 
> Does anyone have any suggestions?  At the moment, the only things I can
> think of doing are either a) shutting down each VM and setting their offset
> to 0 in the vm_dynamic table before starting the back up again or b)
> setting the time forward and back an appropriate amount of time so that the
> offset becomes 0, shutting the VM down and powering it back on again.