[ntp:questions] Odd (mis)behavior when reference clock fails

Unruh unruh-spam at physics.ubc.ca
Wed Sep 24 05:24:02 UTC 2008

hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:

>>It's 4.2.4p4 running on FreeBSD 7.0. The reference clock is a EndRun
>>Tech CDMA clock using the TrueTime driver. When the system was running,
>>ntpq claimed no successful polls of the reference clock or the PPS. It
>>was getting good responses from other systems, but not syncing to
>>them. The offset started small after the clock failed, about .003, and
>>steadily grew to over 5 ms. The reference clock always showed a zero
>>reachability, delay and offset and .001 jitter.

>Do you have a good collection of old log files?

>How about deleting the drift file and restarting ntpd?

>I've seen ntpd get confused when the drift on the system it's running
>on changes by a big step.  I can't think of why a clock dying would
>cause that sort of change, but I don't have any better suggestions.

>I have a Linux box that changes by almost 200 PPM when I turn a
>program on/off.  That program does a lot of serial port activity.
>(It's polling a UPS as fast as it can.)  I haven't tracked it down.

Why would you poll a UPS as fast as you can? This sounds like the old
joke-- Doctor I have a real headache-- What do you do?-- Before it hurts I
bash my head against a brick wall.

It sounds like you are losing timer interrupts.

>I hope FreeBSD doesn't have quirks like that.

>These are my opinions, not necessarily my employer's.  I hate spam.

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