[ntp:questions] NTP client: Sudden time steps on Linux machines

Heiko Gerstung heiko_removeme_.gerstung at meinberg.de
Wed May 2 14:57:28 UTC 2007


Richard B. Gilbert schrieb:
> Heiko Gerstung wrote:
>> Hi Folks,
>>
>> I have a problem on a NTP client, it seems to face sudden timesteps 
>> and I currently do not have any good explanation for this.
>>
>> (NTP Version is ntpd 4.1.2 at 1.892)
>>
>> Apr 24 06:56:50 ntpd[13372]: time reset 0.947095 s
>> Apr 24 06:56:50 ntpd[13372]: synchronisation lost
>> Apr 24 07:23:56 ntpd[13372]: time reset -0.456118 s
>> Apr 24 07:23:56 ntpd[13372]: synchronisation lost
>> Apr 25 03:56:56 ntpd[13372]: time reset 0.949329 s
>> Apr 25 03:56:56 ntpd[13372]: synchronisation lost
>> Apr 25 04:23:53 ntpd[13372]: time reset -0.457310 s
>> Apr 25 04:23:53 ntpd[13372]: synchronisation lost
>> Apr 26 00:57:03 ntpd[13372]: synchronisation lost
>> Apr 26 01:15:09 ntpd[13372]: time reset 1.072991 s
>> Apr 26 01:15:09 ntpd[13372]: synchronisation lost
>> Apr 26 01:38:48 ntpd[13372]: time reset -0.467324 s
>> Apr 26 01:38:48 ntpd[13372]: synchronisation lost
>>
>> This happens on a few machines running in a classified network and I 
>> am not sure if it will be possible to update the NTP on these 
>> machines. I just wanted to know if one of you ever came across such a 
>> behavior or what good (or not so good) reasons could cause this.
>>
>> The logs do not show specific jobs running at those times. According 
>> to my customer the time offset will not be corrected when NTP is not 
>> running (or is told not to correct the clock), therefore I am quite 
>> sure that this is not caused by NTP itself but by some other process / 
>> kernel misbehaviour.
>>
>> But a 1 second jump every few hours? Wow ...
>>
>> Regards,
>> Heiko
> 
> It doesn't look quite that simple.  It's jumping +1, -1/2, +1, -1/2. 
> Something is very wrong there but it's hard to tell what it might be 
> from the evidence presented.

Yes, but the -0.5s step is due to ntpd trying to correct the offset. If 
you do not use ntpd to correct this stuff, it will simply jump in one 
direction and stay there :-( ...

Is there anything I could check or anything you would need to see in 
order to strike out possible reasons?

Regards,
Heiko




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