[ntp:questions] quirky adjtimex behaviour

Hal Murray hal-usenet at ip-64-139-1-69.sjc.megapath.net
Sat Jan 5 22:07:41 UTC 2008

>I am seeing strange behaviour on my _x86_64 Fedora 7 desktop
>workstation with regard to the "system-cmos" time that `adjtimex'

>That leaves the RTC doing the jumping.  But having an RTC that is
>runing nearly 10000 ppm slower than my system clock and which "jumps
>ahead" every 10 seconds seems absurd.

>It seems that leaves two other possibilities: a bug in adjtimex or a
>bug in the kernel.  That's where I am right now.

My guess is that the system/kernel is working correctly and that
the adjtimex utility is printing out misleading stuff.

The CMOS/hardware clock only returns the time to the nearest second.
I think that would cause quirks like this if the code has a loop that
does a bit of work and sleeps for N seconds and the "bit of work"
takes 0.1 second the time when the CMOS clock is read will drift
by 0.1 second each time around the loop.

If you want to play and you can find the source, try changing
the code that reads the CMOS clock to spin in a loop reading
it until it changes.  That will give you the time early in the

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

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