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

Richard B. Gilbert rgilbert88 at comcast.net
Wed May 2 16:14:56 UTC 2007


Heiko Gerstung wrote:
> 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

Is there another program trying to control the clock?




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