[ntp:questions] Sudden change in precision and jitter

Harlan Stenn stenn at ntp.org
Sun Jun 2 19:42:37 UTC 2013


A C writes:
> On 6/2/2013 02:24, David Woolley wrote:
>>> That would be interesting since I have a cron job restarting it at an
>>> odd hour away from any other cron jobs left.  I'll check and see if
>>
>> Why are you restarting it?  ntpd works  best if left to run continuously.
> 
> I know it does...unless there is a bug (a compound bug between ntpd and 
> the kernel) that causes ntpd to spin out of control every few weeks and 
> forces me to restart it anyway.  By spin out of control I do mean that 
> CPU usage goes to near 100% and ntpd stops disciplining the clock after 
> it managed to force the clock to run at some insane rate (e.g. nominal 
> PPM tick adjustment might be -78 and it ramps the tick to +350 PPM over 
> a few minutes).  The end result is that the clock is very wrong, ntpd 
> has totally stopped doing anything, but somehow it's caught in an 
> infinite loop with maximum CPU usage meaning almost nothing else on the 
> system is working right.

It would be really great to run truss or something in this case, and
I would also hope that the GSoC project to upgrade NTP's loggingd and
debugging interface will help with this too.

If you want to open a bug report on this that's fine too - we won't be
able to do much about it until we can repeat it or debug it, but it
might be useful information for the aforementioned GSoC project.

H


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