[ntp:questions] NTP jitter very large

Unruh unruh-spam at physics.ubc.ca
Fri Jun 6 19:57:51 UTC 2008

stephan at newace.ca writes:

>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.

You have LOCAL as a server why? Why in the world would you tell the system
to use itself as a time source. While this might be useful for a server, it
is not for a client. 

>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.

>When I start NTP and query it at several minute intervals, this is the

>After initial startup:
>[root at hydra src]# ntpq -p
>     remote           refid      st t when poll reach   delay
>offset  jitter
> LOCAL(0)        .LOCL.          13 l    -   64    1    0.000
>0.000   0.001
> pbx.... .              INIT.          16 u    -   64    0    0.000
>0.000   0.001

>After 30 seconds:
>     remote           refid      st t when poll reach   delay
>offset  jitter
> LOCAL(0)        .LOCL.          13 l   24   64    1    0.000
>0.000   0.001
> pbx....           time-a.nist.gov  2 u   23   64    1    0.214
>-702.33   0.001

>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 problem occurs whether I initially sync to an internal server or
>NIST directly. The jitter always seems to become very large in a short
>period of time.

And time-a never becomes the server of reference, not does local. 

So that looks like the natural very high drift of your clock. 
It has lost 13 seconds in 30 sec. That is absolutely impossible for ntp to
correct, and indicates a HIGHLY defective system clock. Never mind the

>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?

Your computer clock is completely screwed? Your kernel timer routines are
seriously defective?

>Any assistance would be greatly appreciated.



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