[ntp:questions] NTP Sync Issues

Adam Johnson a.johnson at wintoncapital.com
Mon Jun 9 07:41:15 UTC 2008

Yes you are right we are running RHEL5. The strange thing is that when
we try to sync the servers from a location that syncs correctly normally
to the location with the issues then we get the same issues as the local
servers are experiencing. You say that it could be conflicting time
synchronisation mechanisms, do you mean that the 2 upstream servers are
conflicting or that something other than NTP is causing this? Thank you
for your help!



-----Original Message-----
From: questions-bounces+a.johnson=wintoncapital.com at lists.ntp.org
[mailto:questions-bounces+a.johnson=wintoncapital.com at lists.ntp.org] On
Behalf Of David Woolley
Sent: 08 June 2008 10:20
To: questions at lists.ntp.org
Subject: Re: [ntp:questions] NTP Sync Issues

Adam Johnson wrote:
> We have 3 sites and we are experiencing some strange problems in one
> 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
> 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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