[ntp:questions] NTP jitter very large

Steve Kostecke kostecke at ntp.org
Fri Jun 6 14:33:06 UTC 2008

On 2008-06-06, stephan at newace.ca <stephan at newace.ca> wrote:

> I have a very strange problem that started a few days ago. The server
> is running kernel 2.4.28 and has been running for several years
> without any issues.

Has anything changed on this system?

> When starting the ntp service, the time is initially set correctly
> using ntpdate but after a while, the time will be offset by several
> hours. The longer ntp is allowed to run, the larger the offset appears
> to be. It seems to level off around 6 hours offset.


> After 1 minute:
> remote      refid        st t when poll reach delay offset  jitter
>  LOCAL(0) .LOCL.         13 l    2   64    3  0.000  0.000   0.001
>  pbx...   time-a.nist.gov 2 u    -   64    3  0.157  -20590. 19888.0

This ntpd is configured to use the Undisciplined Local Clock (or
LocalCLK) as a fake time source. Doing so is a bad idea unless this
ntpd needs to serve time to others even when no real time sources are

What is most likely happening is this ntpd is syncing to the LocalCLK
and drifting away from the pbx. Please try running ntpd without the
LocalCLK and post the results here.

We need to see your ntpq -p billboard after this ntpd has synced to one
of those time sources (look for the '*' in the first column) or ~ 20
minutes, which ever comes first. Please condense the billboard lines as
I did above.

> I upgraded from 4.2.0 to 4.2.4b4, but the problem remains. The
> interesting thing to note is that our "pbx" server does not display
> this large jitter and is connected to the same network.
> Does anyone have any suggestions as to why this would be?

You may want to take a look at the Known Hardware Issues and Known
Operating System Issues sections of
http://support.ntp.org/bin/view/Support/TroubleshootingNTP to see if
anything there addresses your problem system.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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