[ntp:questions] NTP Sync Issues

David Woolley david at ex.djwhome.demon.co.uk.invalid
Sun Jun 8 09:20:00 UTC 2008

Adam Johnson wrote:
> We have 3 sites and we are experiencing some strange problems in one of
> the sites. We use NTP to keep the servers in time and this works fine
> for 2 of the sites but in one of the site we get these errors in the log
> ntpd[30062]: synchronized to server, stratum 3
> ntpd[30062]: no servers reachable
> ntpd[30062]: synchronized to server, stratum 3
> ntpd[30062]: time reset +2.119167 s
> ntpd[30062]: synchronized to server, stratum 3

This happens either because of two conflicting time synchronisation 
mechanisms or lost interrupts.

I guess you are running some Unix-like system, from the process numbers 
in the messages.  People failing to identify such systems are usually 
running Red Hat Linux.  Linux (and Windows) are vulnerable to losing 
clock interrupts, especially when using IDE devices in non-DMA modes. 
Red Hat, in particular, tends to set the kernel interrput rate to 1000 
Hz, which tends to exacerbate this.

The typical cause on other Unix systems,  e.g. SunOS and at least some 
versions of SCO Unix, is software that resets the software clock from 
the real time clock.

Tickless Linux systems are too new for much experience of failure modes 
to have been gathered.

What one can reasonably say is that is is an OS or hardware issue, not 
an NTP one.

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