[ntp:questions] Clock skew changes drastically between reboots

Spoon devnull at localhost.com
Tue Apr 3 07:29:39 UTC 2007


Ronan Flood wrote:

> Spoon wrote:
> 
>> I rebooted the computer at 10:38:26
>> 
>> I removed the drift file and started ntpd.
> 
> Why did you remove the drift file?  It is there to provide some
> state when restarting ntpd.

On these systems, after a reboot, the value in the drift file is 
completely wrong. Letting ntpd think that it is an appropriate 
approximation slows down the computation of the new frequency offset.

I followed Professor Mills's methodology.
http://ntp.isc.org/bin/view/Support/HowToCalibrateSystemClockUsingNTP

    1. Run ntptime -f 0 to remove any leftover kernel bias.
    2. Configure for a reliable server over a quiet network link.
    3. Remove the frequency file ntp.drift.
    4. Start the daemon and wait for at least 15 minutes until ntpq -c 
rv shows state=4. Record the frequency offset. It should be within 1 PPM 
of the actual frequency offset. For enhanced confidence, wait until the 
first frequency file update after one hour or so.




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