On 08/01/2008 15:15, Brian Mathis wrote:
From: Jack Bailey <jack@xxxxxxxxxxxxxxx>
Date: Jan 8, 2008 3:17 AM
To: centos@xxxxxxxxxx
Hello All,
Consider a CentOS-5.1 Xen server (2.6.18-53.1.4.el5xen) hosting two
domains running CentOS-5.1 (2.6.18-53.1.4.el5). One domain has a fairly
accurate clock, the other domain has a clock that gains ungodly amounts
of time, roughly one minute every two or three minutes. For a fix, one
suggestion is to run this command in DomU:
echo 1 > /proc/sys/xen/independent_wallclock
This didn't change anything. As an experiment, I wrote a script to call
ntpd -q, sleep 60, and repeat indefinitely. Here are a couple of
snippets of output:
goodclock# ksh ./xenclockdrift
ntpd: time slew +0.001211s
ntpd: time slew +0.001200s
ntpd: time slew +0.001855s
ntpd: time slew +0.001532s
ntpd: time slew +0.001603s
ntpd: time slew +0.001320s
ntpd: time slew +0.001931s
badclock# ksh ./xenclockdrift
ntpd: time slew -0.000193s
ntpd: time set -57.356377s
ntpd: time slew +0.002352s
ntpd: time slew +0.003018s
ntpd: time set -57.417488s
ntpd: time slew +0.012089s
ntpd: time slew -0.000985s
These domains are fully virtualized and set up identically, except
"badclock" is allocated two processors versus one processor for
"goodclock". DomU's clock is running normally.
Anyone know what's going or know how to fix it?
Jack
I'm not sure with Xen, but on VMWare one should not be using NTP at
all. Time syncing should be done with the vmware tools and the host,
with NTP only running on the host (not the guests). Using NTP on a
vmware system will result in similar behavior to what you are seeing
here.
At least, that is the theory. Empirically, using the vmware tools time
sync feature will push a slow VM's clock forwards, but it won't push a
fast clock backwards. I'm yet to see a "best practice" for ensuring
proper time synchronisation within VMware VMs, but for now, NTP seems
the best option.
cheers
Luke
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