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Re: [Xen-users] Time went backwards

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Andy Smith <andy@xxxxxxxxxxxxxx>
  • Date: Sat, 6 Oct 2007 19:34:52 +0000
  • Delivery-date: Sat, 06 Oct 2007 12:35:43 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Openpgp: id=BF15490B; url=http://strugglers.net/~andy/pubkey.asc


On Sat, Oct 06, 2007 at 10:26:48AM +0200, h9802641@xxxxxxxxxxxxx wrote:
> I am running this command hourly (cron) within the Dom0.
> ntpdate -s ts1.univie.ac.at at.pool.ntp.org ptbtime1.ptb.de

I would strongly advise not doing this, and instead running an
ntpd.  That goes for both Xen and non-Xen machines.

Not only can ntpdate cause the clock to step backwards, but if one
of the servers you list had its clock set wildly wrong then yours
would get set wildly wrong too if it ever ran ntpdate against it.

> I havent touched the time / date settings of the DomUs anyhow. Should I?

In theory a domU is supposed to keep its clock locked to that of the
dom0, so one only needs to run ntpd in dom0.

However I have never found that to be reliable so have had to set
/proc/sys/xen/independent_wallclock to 1 and run ntpd in every domU


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