xen vm not keeping date/time properly

Northrup, Wilson wilson_northrup at merck.com
Thu Jan 22 22:21:14 UTC 2009


Have you or are you using the tickless kernel with this setup, and does
that make a difference?


-----Original Message-----
From: redhat-list-bounces at redhat.com
[mailto:redhat-list-bounces at redhat.com] On Behalf Of Ryan Golhar
Sent: Thursday, January 22, 2009 2:45 PM
To: General Red Hat Linux discussion list
Subject: Re: xen vm not keeping date/time properly

George Magklaras wrote:
> Ryan Golhar wrote:
>> says xen just passed the time-related calls to Dom0, but that

>> can't be the case because the times are different.
> That is because if you do run ntpd inside the VM, this can create the 
> problem.
>> noselect?  inside the VM?
> Yes on the guest system, and run ntpd normally on the Dom0.

I'm running ntpd normally on the host, and ntpd inside the VM using the 
noselect parameter on the server line, such as:

server siriusc.umdnj.edu	noselect
server 0.rhel.pool.ntp.org	noselect
server 1.rhel.pool.ntp.org	noselect
server 2.rhel.pool.ntp.org	noselect

After about a half hour after restarting the ntpd server inside the 
guest, I'm noticing clock skew of about 30 seconds.  I'm sure this will 
continue to grow.

Anyone have any other ideas?

I'm surprised there isn't a solution to this.  This is a huge problem, 
especially for an enterprise system that relies on the date/time being 


>> We are running on a Sun SunFire X4150.
> What I stated was on a Dell 2950 PowerEdge, but I shall get hold of a 
> SunFire and repeat the test, see if I get the same issue. It does
> that there might be some kernel parameters that need tweaking, but, I
> curious to find out what's going on, as we will be using SunFire kit 
> with Xen soon.
> GM
>> George Magklaras wrote:
>>> This page might offer some help:
>>> http://support.ntp.org/bin/view/Support/KnownOsIssues#Section_9.2.2.
>>> To recap, we use the 'noselect' keyword to avoid the running ntpd on

>>> the client to attempt to sync with the defined servers and ntpq does

>>> not report any disturbing drifts on the client...and we do run ntpd 
>>> normally (no 'noselect') on Dom0.
>>> What happens (happened if you have already tried) if you try and do 
>>> this? And what's your hardware platform?
>>> GM
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