[ntp:questions] ntpd and database servers

Rob nomail at example.com
Thu Jan 14 22:48:09 UTC 2010

nodata <lsof at nodata.co.uk> wrote:
> Am 2010-01-14 20:38, schrieb Rob:
>> You could stop ntpd, and then use the adjtimex program to set the
>> clock rate to a slower value, so that the systems will lose time.
>> (using the --tick option)
>> Calculate how long it is going to take to arrive at the correct time
>> using the setting you decide on, and then come back to the system
>> (probably put an alert in your electronic calender) to check that the
>> time is slightly behind correct time.
>> Then reset the adjtimex setting to the normal rate and restart ntpd.
>> It will probably jump forward a little at that moment but that should
>> not matter.
> Thanks for this.
> Would you mind explaining the link between CONFIG_HZ and the tick value? 
> The example in the man page is not clear (it uses the same tick value as 
> I have on a CONFIG_HZ=1000 box). Is the statement "Increasing val by 1 
> speeds up the system clock by about 100 ppm, or 8.64 sec/day." always 
> true, whatever the CONFIG_HZ value?

The manual page explains it as if the value of tick is dependent on
the HZ value but that does not appear to be true in reality.
I would use "adjtime -p" to find the value (10000 on my system even
though HZ is 250) and then assume that changing it by 1 changes the
clock rate by 1/10000 (or 100 ppm, just as the manual says).

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