time drift

[David Kelly]

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 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

[...]

> 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
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Whom computers would destroy, they must first drive mad.