time drift

David Kelly dkelly at hiwaay.net
Thu May 15 21:08:23 UTC 2008

On Thu, May 15, 2008 at 08:57:59PM +0200, 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 offset -13.799602 sec
> 15 May 10:36:48 ntpdate[7515]: step time server offset -12.813941 sec
> 15 May 11:06:48 ntpdate[7879]: step time server offset -13.651921 sec
> 15 May 11:36:50 ntpdate[8079]: step time server offset -11.109298 sec
> 15 May 12:06:50 ntpdate[8289]: step time server offset -11.836499 sec


> What would be your suspicion on the large time drift of the FreeBSD
> 6.2 system?

Its PC commodity-grade. Not all that unusual even for stuff sold
claiming to be a "server". This is in no small part why ntpd exists.

nptd calculates a correction coefficient and (under FreeBSD) stores it
in /var/db/ntpd.drift for use on next start so as to more quickly
establish a lock.

So in short ntpd calibrates your clock in order to minimize the
corrections required. Is The Right Thing To Do.

David Kelly N4HHE, dkelly at HiWAAY.net
Whom computers would destroy, they must first drive mad.

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