[ntp:questions] NTP jitter very large

Unruh unruh-spam at physics.ubc.ca
Fri Jun 6 19:59:45 UTC 2008

Steve Kostecke <kostecke at ntp.org> writes:

>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.

It cannot. It is driftine at 130000 PPM, which is way way way outside of
NTP's range. 

>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.

It will never sync with that kind of drift rate.

>> 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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