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[Xen-users] Re: Time synchronization issue

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Subject: [Xen-users] Re: Time synchronization issue
From: Diego Molina <diegoaugustomolina@xxxxxxxxx>
Date: Tue, 12 Jul 2011 13:12:31 -0300
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2011/7/7, Diego Molina <diegoaugustomolina@xxxxxxxxx>:
> Hi, I have Gentoo Linux dom0 and paravirtual domUs with Xen 3.4.2 all
> of them with `/proc/sys/xen/independent_wallclock' set to 0 (dom0 and
> domUs) but domUs aren't in sync with dom0.
> I've noticed this after a while, because I saw a recent line in a log
> file with the time in the future. Then I went to the dom0, set time
> quickly with ntpdate and started ntpd. After this I noticed that all
> domUs still had the same time so I waited... and waited to see the
> changes take effect. Nothing happened. It's been a day since then, and
> I can see dom0 and domUs are all acting as if they were configured to
> use the independent wall clock. I was able to change the time of one
> of the domUs and still see it differs both from dom0 and the other
> domUs. I googled and searched the archives but couldn't find a way
> out. It would really mean a lot to me not to have to maintain ntp in
> all domUs...
> Thanks a lot for your job!

Even stranger:
1) I Shut down one domU and created it again. Not even at start up the
clock was correct. It keeps wrong. I've noticed that after a while of
changing the system time it rolls back to the wrong state again in a
consistent manner, so that all domUs end up with a similar (not equal)
wrong time. One may think it may be due to a /etc/localtime (or
similar) misconfig, but the drift is given within minutes, not *exact*
hours (that's an easy way to discard that option).

2) Not even ntp could keep the time correct in the domUs!!!! Ok, this
is serious. Once in a while the time was correct (after a sync), then
it went wrong as much as it could.

3) This morning we had to shut the whole rack down due to a general
upgrade and mantainance. When I booted all machines the time was
correct again everywhere! This is straaaange, and I have the
impression that this can be caused by a continuous process of drifting
during the dom0 uptime. Even with an obscure explanation like this it
is still strange.

I started to think about a hardware failure, even been a new server
(about five months old) but couldn't find anything bad with standard
tools. Also, time was well kept in dom0 so that may mean hw is ok too.

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