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Re: [Xen-users] NTP on fully virtualized domUs

To: Peter Mueller <peter.mueller@xxxxxxxxxxx>
Subject: Re: [Xen-users] NTP on fully virtualized domUs
From: Martin Kraus <lists_mk@xxxxxxxxxxx>
Date: Tue, 11 Nov 2008 12:11:53 +0100
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On Tue, Nov 11, 2008 at 11:24:28AM +0100, Peter Mueller wrote:
> >> first you have to run ntpd in Dom0 and let him sync to some
> >> timeservers on the web. This ntpd can sync the hardware clock,
> >
> > Sure? I think only hwclock can set the host's RTC.
> Yes, that's right. But hwclock is often called on shutdown (if
> configured) and grabs it's time from the machine it was started. I'm
> not really, but 90%, sure thta ntpd can set the hardware clock too.
> But back to the main problem: For paravitualized DomUs you MUST
> configure yout ntpd's the described way. And I think, that full
> virtualized DomUs can't access the hardware clock directly too. Please
> correct me, if i'm wrong. Haven't setup that much full virtualized
> Machines.

i'd bet xen keeps virtual hardware clocks for each domU. I'm running time
server, part of pool.ntp.org, without any problems. to setup time, just instal
ntpd and make sure that /proc/sys/xen/independent_wallclock is set to 1

echo 1 > /proc/sys/xen/independent_wallclock

or put this in /etc/sysctl.conf


it might also be possible, that running ntpd on dom0 and setting
independent_wallclock to 0 will keep your time accurate, but i'm not sure and
i'm too lazy to test it.


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