[ntp:questions] NTPd looses sync regularly / 12 hour intervals.

Martin Burnicki martin.burnicki at meinberg.de
Mon Sep 13 12:43:56 UTC 2010


sorry for the late reply.

Michael Nielsen wrote:
> Here are some more details from the ntp logging - ntp_mon peerstats..
> It's doesn't seem to be a interrupt creep, as the server is maintaining
> time properly all day, except for 30 mins each day.

So once again this meets perfectly my assumption. The system time is stepped
by some program, and a few minutes later ntpd steps the system time back.

And, since your first post the offset between the time sources used by ntpd
and the reference time used by the extra program has increased from about
70 seconds to to 87 seconds ...

> So I guess it's a program I need to look for, any ideas as to what I
> should look for ?

Unfortunately not. This can be any program calling "ntpdate -u" or rdate or
whatever in some intervals.

Some time ago I had a customer who tried to set synchronize computer times
using NTP, and we found out he had a 3rd party client/server application
running where the client "synchronized" its time to its server's time in
periodic intervals, using a proprietary protocol with 1 s resolution only.
This messed up all attempts by ntpd to get the system time synchronized
properly because the maximum error was always 1 s due to the granularity of
the protocol.

Anyway, that was under Windows, but basically the OS doesn't matter for
cases like this.

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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