[ntp:questions] ntpd goes into oscillation

David J Taylor david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Wed Dec 30 09:27:30 UTC 2009

"unruh" <unruh at wormhole.physics.ubc.ca> wrote in message 
news:slrnhjkta6.4e4.unruh at wormhole.physics.ubc.ca...
> ntpd has suddenly broken out into oscillations. it is fed by a Garmin
> 18 LVC PPS via shm. The oscillation has a period of just under an hour (
> about 50 min) and an amplitude of about 10usec. in the offsets (
> amplitude of about .005PPM in the rate). Since this is acting as the
> clock for a number of other machines, they are also showing the
> oscillation especially in the rate.
> While I suppose this could be something in the GPS itself, it looks more
> like an oscillation in ntpd.
> Nothing changed when the oscillations started. Ntpd had been started
> on Dec 14, and this change began on Dec24.
> You can see the graph on www.theory.physics.ubc.ca/chrony/chrony.html ,
> the graph for the machine called string.
> Has anyone else ever seen this kind of thing?

Something similar, perhaps, yes, and I reported it here before.

It seems that NTP hits the +/- 500 ppm drift limit and can't recover - 
check the drift file contents.  You might try deleting (or renaming) the 
drift file.  I haven't seen this for some time, though.  What version are 
you running?


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