Re: [Xen-users] time synchronization problem (using NTP)

[Thomas Harold <tgh@xxxxxxxxxxxx>]

Ulrich Windl wrote:
> On 11 Oct 2006 at 19:02, Christoph Purrucker wrote:
>
> > Hi Thomas,
> >
> > > As far as my experience shows, none of the ntp / independent_wallclock 
> > > combinations work. We got the same problem here with xen 3.0.2 and 
> > > kernel 2.6.16. It looks like ntpd can't set the time in DomUs with 
> > > independent_wallclock set to 1 but the DomUs aren't using the exact time 
> > > of Dom0 with independent_wallclock set to 0.
> > I'm running 2.6.16-2-xen-k7 with XEN 3.0 on both Dom0 and DomUs. A cron 
> > job on Dom0 runs "ntpdate ptbtime1.ptb.de" every night (shifting the 
> > time some milliseconds). All DomUs are perfectly in sync. 
> > /proc/sys/xen/independent_wallclock = 0 in all DomUs.
> A plain "ntpd" also does the job once XEN's own synchronization (wich must be 
> buggy) is disabled (sysctl -w xen.independent_wallclock=1):
Just a small update and a question.

Before setting wallclock=1 (mine was set to 0), the ntpd in my DomU was 
running about 2 minutes fast.  There were entries in the ntpd.log file 
indicating that it was setting the clock back by 141 sec, but the "ntpq 
-p" output still showed an offset of 141 sec (-141000 msec).
Now it seems to be working properly (ntpd is now able to adjust the clock).

The ntp.conf file in the DomUs looks like:

server time1.example.com iburst
server time2.example.com iburst
server time3.example.com iburst
server time4.example.com iburst
server time5.example.com iburst
driftfile       /var/lib/ntp/ntp.drift
restrict default nomodify nopeer
restrict 127.0.0.1

(The timeN.example.com are our internal time servers.  These are usually 
Dom0s.  They currently access public servers but may eventually talk to 
a GPS clock directly.)
Still using Xen 3.0.2 here w/ the latest NTP version.

...

Will the sysctl command make that a permanent change?  Or do I need to 
edit /etc/sysctl.conf and add that line at the end?  (I'd guess that I 
need to add that in my DomUs.)

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