[ntp:questions] Re: strange sign change in clock drift with linux

mike michael.no.spam.cook at wanadoo.fr
Mon Apr 17 13:29:13 UTC 2006

Forgot to add:
It is also showing horrible jitter as well as sign change.

mike wrote:
> Yesterdaw I upgraded my linux kernel from to in order 
> to take advantage of the PPSKit. I have changed neither the NTP version 
> nor the config. After rebooting and checking that all
> was working, I noticed that the calculated local drift had switched
> from its former stable -32 ppm to a positive value of +27 ppm. Over the 
> past 4 years it has been recorded as being the negative figure over
> numerous upgrades of both kernel and NTP code.
> The positive value stayed stable over 24hrs, so I then rebooted the 
> kernel to see if it reverted, and sure enough it drifted back to 
> -ve , getting to near its normal value after about 3hrs,
> [mike at quark KERNEL]$ cat  /var/tmp/ntpdrift-
> 26.992
> [mike at quark KERNEL]$ cat  /etc/ntp/drift
> -32.176
> NTP seems to be adjusting to the percieved change as it doesn't appear 
> to have had any effect in relation to the offset I am seeing with 
> external servers such as NIST (not in my server config).
> [mike at quark KERNEL]$ ntpdate -d time-nw.nist.gov
> ...
> delay 0.22145, dispersion 0.00163
> offset -0.007404
> Has anyone else seen such changes?

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