Re: clock suddenly slipping behind
Stefan O'Rear <stefanor@cox.net> said on Thu, 26 Aug 2004 20:34:17 -0700:
> On Thu, Aug 26, 2004 at 11:23:07PM -0400, Nori Heikkinen wrote:
> > over the past few days, i've noticed that my system clock gets about
> > ten to fifteen minutes slow over the course of a day. this is really
> > weird! i've been using ntpdate to synchronize it with a timeserver
> > whenever i notice it, and i put it in a once-a-day cron job, but i
> > want my system to ALWAYS be on time. i'm confused as to what's
> > causing this, and how i can fix it. any ideas?
>
> Perhaps your PIT is going south? (PIT = Programmable Interval Timer,
> a variable-frequency timer usually set to 100HZ by Linux.)
Nope. This seriously needs investigation.
http://www.google.com/groups?selm=2qVhI-80D-5%40gated-at.bofh.it
The one replyer said he didn't see anythign wrong.
I had 2 machines with ntp packages and adjtimex querying two known
good upstreams, plus three pool.ntp.org servers, that upon upgrade of
sid a couple of weeks ago, broke at the rate of ~12 and ~14 seconds
per 10 minutes (for my two machines, very constant for each), which
was ~twice the rate that the OT reported). One went through a kernel
reboot and the other didn't, so it wasn't a new kernel issue.
Uninstalling ntp and adjtimex and reinstalling didn't fix.
Uninstalling, *purging* (so drift file and config files gone),
*rebooting*, and then reinstalling fixed. Doing one or the other of
rebooting and purging was not good enough - the kernel keeps state in
one case, and the ntp drift files etc keep state in the other case.
I haven't tried to reproduce this, but things to note were the drift
file *seemed* to have normal contents, the adjtime file was slightly
off (but should only affect the hardware timer anyway, and was
probably off because ntp was so confused - you can't calibrate the
hardware clock off a faulty software clock).
One other very clued in guy on the scary devil monastery also found
this problem a day or two ago. I've been in communication with him,
and it seems these are all related. There is a hard to trigger bug
somewhere, but if you want to track it down, you'll prbablky need to
reinstall old version of ntp and/or adjtimex and just keep working
forwards and backwards until you trigger the bug again.
--
TimC -- http://astronomy.swin.edu.au/staff/tconnors/
Computers are not intelligent. They only think they are.
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