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Re: [Xen-devel] Dom0 <> DomU clock sync

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Dom0 <> DomU clock sync
From: Sébastien RICCIO <sr@xxxxxxxxxxxxxxx>
Date: Mon, 03 Sep 2007 16:07:13 +0200
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Hi Keir,

Thank you for your answer.

Ntpd is not running in dom0. I am updating the dom0 time with ntpdate (crontab every hour).
Should ntpd be running on dom0 ?

[root@xen01 /]# date
Mon Sep  3 15:59:37 CEST 2007

DomU (started 5 hours ago)
ns1 bin # date
Mon Sep  3 15:58:05 CEST 2007

ns1 bin # uptime
15:58:10 up  5:21,  3 users,  load average: 0.00, 0.00, 0.11

But this is strange... I just rebooted the vm:

[root@xen01 /]# date
Mon Sep  3 16:04:13 CEST 2007

ns1 ~ # date
Mon Sep  3 16:02:41 CEST 2007

There is already a difference when the vm is freshly rebooted.
Same after a shutdown/xm create....

Weird... Any idea ?

Thanks again!

Sébastien Riccio
SwissCenter / OpenBusiness SA

Keir Fraser a écrit :
You're not running ntpd in the domU as well, right? Just worth checking...
Apart from that I don't think you can be doing anything wrong. Any weirdness
after long uptime is of course interesting, as it's something that's hard
for developers to test.

If you create a new domU (doesn't need to be from scratch installation -
e.g., just restarting a domU, or starting an existing dormant domU, would
do) then is its time behind dom0, or in sync?

 -- Keir

On 3/9/07 08:45, "Sébastien RICCIO" <sr@xxxxxxxxxxxxxxx> wrote:

Hello !

Just a quick question about time synchronization between xen dom0 and

We're running Xen 3.1 64-bit, with 32 and 64 bits linux guests.

It's up since 89 days and the domU's time is around 5 minutes behind the
which is updated via ntpdate...

Any idea why it doesn't sync the guests even that
/proc/sys/xen/independent_wallclock is 0 ?

Could it be an option that I missed in dom0/domU kernel ?

Thanks for your help !

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