[ntp:questions] Strange jumps in PPM

A C agcarver+ntp at acarver.net
Thu Aug 22 14:25:25 UTC 2013


On 8/21/2013 23:57, David Woolley wrote:
> On 21/08/13 21:24, A C wrote:
>
>>
>> So the idea isn't that ntpd should figure out on its own without user
>> intervention.  Instead there would be some kind of
>> configuration/fudge/tinker options available so that the user can supply
>> baseline information that can help ntpd identify a rogue source versus
>> normal system behaviors.
>
> Actually, one of the main complaints about ntpd is that it favours the
> theory that the source is the problem, when the crystal temperature is
> the real problem.  (The exception to this is people who manually yank
> the local clock and then complain that ntpd doesn't immediately reset it.)

In most cases of steady drift or cyclical drift that may be true and I 
certainly do see temperature effects on my system over the course of a 
day.  However in this particular case I can pretty much guarantee that 
it's the source that caused the problem.  I certainly didn't have a 
temperature swing large enough to change the clock rate from -76 to -34 
PPM in 16 seconds and then have it go back to -76 after 128 seconds (8 * 
16) especially considering I was sitting in the room at the time it 
happened staring at a thermometer that looks at the internal temperature 
of the machine.  The nominal swing caused by temperature on my system is 
about 2-3 PPM (-76 to -73 or so) for an internal temperature swing of 
about 10 degrees Fahrenheit.



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