[time-nuts] Tracking NTP displacement and correlationbetweentwo clients.

[Christopher Brown]

That is his point.

Initial time comes from MB clock.

System (OS) time is set from that at boot.

During NTP startup for a client it is normal to do a "ntpdate" to hard
set the OS clock (direct one time set).

>From there ntpd would track and adjust.

HOWEVER, there are limits to how much ntpd will skew the clock to keep
it in sync.  If the OS clock is drifting faster than this amount ntpd
will not be able to adjust it fast enough.


Think bad hardware or buggy BIOS, OS clock ends up running too fast or
too slow for ntpd to compensate for.



On 10/5/12 12:46 AM, David J Taylor wrote:
> David,
> 
> The problem is that they start in sync and over the course of a day drift 
> that far apart despite having NTP running. We're not sure why NTP isn't 
> correcting it along the way. Though at this point, we are looking at a 
> firmware bug.
> 
> Thanks!
> Bob
> ===================================
> 
> Bob,
> 
> I take it that you are booting the PC at the start of the day, and it syncs 
> to NTP servers at that time?  If the internal clock is off (when 
> undisciplined) by more than 500 ppm (43 seconds/day) NTP will not control 
> it.  I suggest measuring the clock error when it is not being controlled by 
> NTP, and then we can progress.  (Or you find the firmware problem).
> 
> Cheers,
> David
>