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

["Roger Lucas" <roger@xxxxxxxxxxxxx>]

Firstly, I am really not a clock expert....

> On 11 Oct 2006 at 14:09, Roger Lucas wrote:
> 
> > Have you tried chrony ?
> 
> Hi!
> 
> As I sayid months before, NTP is not designed fo fix a bad clock 
> implementation,
> so does chrony? I'm tempted to say: if NTP is unable to work inside XEN, but
> succeeds outside, there's a problem with XEN.
> 

As I understand it, chrony will constantly adjust the system clock time to keep 
it in line with the remote NTP servers.  It can
track frequency drift etc so your system clock changes are as smooth as 
possible.


> >
> > We use chrony on our Xen-3.0.2-2 servers and it is happily running on both 
> > Dom-0 and the Dom-Us.
> >
> > If you are running (K)Ubuntu and have "universe" repositories enabled, 
> > installation is as simple
> as "apt-get install chrony".  A
> > quick change to "/etc/chrony/chrony.conf" to set the NTP servers you want 
> > to use and (if you are
> reliably connected to the Internet)
> > removing the "offline" parameter for them will have you ready to (re-)start 
> > the chrony daemon and
> sync the clocks.
> >
> > FWIW, we have "/proc/sys/xen/independent_wallclock" set to 0 on the Dom0 
> > and the DomU's.
> 
> That seemed to have helped (just running for a short time now):
> 
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> *rkdvmso1.dvm.kl 192.168.0.11     5 u   17   64  377    0.072   -6.540   0.009
> +rksapas01.dvm.k 192.168.0.61     6 u    8   64  377    0.123   -2.231   0.006
> *rkdvmso1.dvm.kl 192.168.0.11     5 u    1   64  377    0.080   -4.302   0.053
> 

We have tried several different NTP-based solutions to keep all our servers in 
sync and chrony is the only one that has worked
painlessly on every platform we have tried including several different linux 
distributions and VMs.  Don't ask me to list the ones
that didn't work - it was a long time ago and I can't remember the details any 
more.

IMHO, chrony is one of the wonderful *nix tools that "just works".

Don't forget, however, that chrony takes some time (IIRC about 15 mins) to 
synchronise up to the remote servers and accurately
calculate the system time error.  Only when it has an accurate estimate of the 
error will it start to adjust the local system clock.

BR,

Roger


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