[ntp:questions] "ntpd[7602]: synchronized to"

Miroslav Lichvar mlichvar at redhat.com
Thu May 26 17:48:30 UTC 2011

On Thu, May 26, 2011 at 09:49:55AM -0700, Chuck Swiger wrote:
> On May 26, 2011, at 9:28 AM, Florin Andrei wrote:
> > On 05/23/2011 03:57 PM, Chuck Swiger wrote:
> >> 
> >> That being said, it's not expected that the preferred time source
> >> would change that frequently.  You'd probably do better to run
> >> with at least 4 servers, so that it can better judge their
> >> reliability; with only two, there isn't much basis for
> >> comparison.
> > 
> > So, basically you're saying the "quality" of the NTP servers
> > fluctuates for some reason and this machine is flipping back and
> > forth between them?
> Evidently yes for your case.  With only two servers, it may not be
> possible to find a best intersection via ntpd's variant of
> Marzullo's algorithm:

I think the frequent source switching can happen with any number of
sources if the two best servers have similar synchronization distance.
With more servers you may have a better chance that the best server is
significantly better than the others though.

The problem can be usually fixed by increasing the anti-clockhopping
distance by "tos mindist", perhaps to 10 ms.

Miroslav Lichvar

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