I am seeing a very severe clock drift on my Xen HVM VPS, rented from a hosting provider, so I don't have access to the dom0 system. I continuously run ntpd, but the clock drifts by as much as 30 seconds in 5 minutes and NTP cannot keep up. Has anyone experienced this?

Here are some details:

$ dmesg | grep clock
[    0.160000] Measured 347 cycles TSC warp between CPUs, turning off TSC clock.
[    0.396000] * this clock source is slow. Consider trying other clock sources
[    0.550448] Switching to clocksource acpi_pm
[    0.653135] rtc_cmos 00:05: setting system clock to 2011-03-09
02:45:40 UTC (1299638740)

$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource 

$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource 
  • You could use the tinker panic 0, and tinker step options in your ntp.conf. This will allow it to make corrections faster. Not sure what you need to do to fix the real problem though.
    – Zoredache
    Mar 9, 2011 at 21:24

3 Answers 3


Add this line to the beginning of ntpd.conf:

tinker panic 0

That will help it keep up. Here is a link to the vmware best practices for timekeeping. I know you're not using vmware, but much of it should still be applicable.

  • For whatever reason that doesn't work: Restarting openntpd: /etc/openntpd/ntpd.conf:16: syntax error Which is the line on which I added tinker panic 0. I am using openntpd 3.9p1+debian-5 on Ubuntu 10.10 2.6.35-22-generic-pae i686.
    – ipartola
    Mar 9, 2011 at 21:35
  • I missed the part about openntpd. Losing ticks is common (and nearly unavoidable) in a virtual world. You're going to need to get ntp to keep up somehow. Can you run "regular" ntpd on the box?
    – Chris
    Mar 9, 2011 at 21:50
  • Yes, I installed ntp instead of openntpd and added the "tinker panic 0" line to the config file; then restarted ntpd. So far the time has not changed.
    – ipartola
    Mar 9, 2011 at 22:41
  • By "not changed" do you mean in the good way or the bad way?
    – Chris
    Mar 10, 2011 at 15:23
  • Sorry for the confusion. I mean in a bad way: as in the time is still wrong.
    – ipartola
    Mar 23, 2011 at 15:42

I recall that being an issue in guests some time back, but I couldn't recall how to get around it or fix it. So I googled and got this solution.

Uninstall openntpd

Then create a cron job with the following script.

#! /bin/bash
# This is a DIRTY hack to allow have time settings correctly on Xen guests
# clopez@igalia.com
echo 1 > /proc/sys/xen/independent_wallclock
ntpdate -b pool.ntp.org 0.debian.pool.ntp.org hora.roa.es
echo 0 > /proc/sys/xen/independent_wallclock

This is based on the advice from this link: http://blog.neutrino.es/2010/workaround-for-the-time-drift-issue-on-xen-keep-your-guests-synced/

Let me know if it works for you.

  • Thanks for the reply. I have since left the VPS provider that had this issue so I cannot say whether this works or not, but it sounds plausible. I cannot accept an answer as I cannot verify, but have an upvote.
    – ipartola
    Jul 18, 2013 at 15:28

On XEN 4.4.x server host, you can set the property tsc_mode="native" for your vm guest in file /etc/xen/vm.conf. Then, you can startup your vm and inside your vm os make a cronjob to perform a periodically synchronize time from an external ntp server.

This worked for me.

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