[ntp:questions] Increase maximum frequency offset to deal with really bad clock

Unruh unruh-spam at physics.ubc.ca
Wed Jan 28 22:42:22 UTC 2009


"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:

>jeff at sailorfej.net wrote:
>> Hi folks,
>> 
>> I have a some FreeBSD systems running as guests in Microsoft Virtual
>> Server.  There is a known problem with these were the clocks run very
>> fast.  I am trying to use ntpd to keep their clocks in sync, but the
>> frequency error offset is exceeding (I think) ntpd's maximum of 500,
>> my driftfile always contains a value of "-500.000".  If understand the
>> way this works correctly, if I could get the frequency error offset to
>> represent the real error rate which I believe to be much higher that
>> 500 PPM, then ntpd would be able to keep the clocks in sync, as it is
>> now, it slowly falls behind until it fails to correct altogether.
>> 
>> So is it possible to override the maximum offset PPM in the driftfile,
>> or is there a better way to fix this?
>> 
>> Thanks,
>> Jeff

>I'm not familiar with BSD but if there is a way to reduce the speed at 
>which the clock ticks, using it MIGHT bring the clock close enough that 
>NTPD could discipline it.   The 500 PPM limits translate to +/- 43 
>seconds per day so, if your clock is outside the limits it is REALLY 
>off.  The cheapest wrist watches do better than that!!
You are running one operating system on top of another. There is lots of
paging out, suspending, etc. I would be surprised if you got accuracy of 5
hours per day, never mind seconds per day. And I would expect it to be
highly variable. The rate would be all over the place. YOu either need to
set things up so that our BSD gets it time from the MS system, and have the
MS system run ntp, or give up on time altogether. I would be surprised if
this situation could be fudged so as to give at all reasonable time for the
BSD ssytem.





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