time drift

Chuck Swiger cswiger at mac.com
Thu May 15 19:18:58 UTC 2008


On May 15, 2008, at 11:57 AM, Volker Jahns wrote:
> FreeBSD 6.2 running on X86 hardware (FSC) shows a remarkable time  
> drift
>
> running ntpdate every half hour shows that the system looses about  
> 10-14 sec each time.
> 15 May 10:06:48 ntpdate[7200]: step time server 192.53.103.108  
> offset -13.799602 sec
> 15 May 10:36:48 ntpdate[7515]: step time server 192.53.103.108  
> offset -12.813941 sec
> 15 May 11:06:48 ntpdate[7879]: step time server 192.53.103.108  
> offset -13.651921 sec
> 15 May 11:36:50 ntpdate[8079]: step time server 192.53.103.108  
> offset -11.109298 sec
> 15 May 12:06:50 ntpdate[8289]: step time server 192.53.103.108  
> offset -11.836499 sec

While you should run ntpdate -b at system boot, running ntpdate  
periodically via cron is not the right thing to do-- you should run  
ntpd instead, and that will figure out the intrinsic correction your  
chosen system clock needs to keep better time via the ntp.drift file.

You should also take a look at the output of "sysctl  
kern.timecounter", and possibly switch to a different mechanism, if  
the existing choice doesn't work out well for your machine...

Regards,
-- 
-Chuck



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