[ntp:questions] Can a clock drift be too big for ntpd?

Harlan Stenn stenn at ntp.org
Sat Oct 20 00:44:26 UTC 2007

>>> In article <slrnfhg0ap.vl7.pln at glast2.Stanford.EDU>, Patrick Nolan <pln at glast2.Stanford.EDU> writes:

Patrick> I'm having trouble with one linux client out of a group.  It seems
Patrick> as if ntpd can't keep its clock syncronized.  It's drifting about
Patrick> 6-10 minutes per day, well over the 500 ppm limit.

As others have noted, ntpd cannot help in this situation, if it cannot be
corrected.  See http://support.ntp.org/Support/TroubleshootingNTP for more

Patrick> After reading some of the posts on this newsgroup, I have come to
Patrick> realize that debugging ntp problems can be quite complex.  Before I
Patrick> launch into a detailed search, I would like to clarify one
Patrick> question.  Is it possible for the clock frequency to be so far off
Patrick> that ntpd just can't get it under control?

Yes, but be sure to rule out hardware *and* OS issues first.  See above.

Patrick> I have stripped my ntp.conf to the minimum, just one server line
Patrick> and a drift file.  The log entries look like this:

Patrick> Oct 18 17:23:32 client ntpd[30920]: synchronized to,
Patrick> stratum 1 Oct 18 17:27:48 client ntpd[30920]: no servers reachable
Patrick> Oct 18 17:29:06 client ntpd[30920]: synchronized to,
Patrick> stratum 1 Oct 18 17:29:16 client ntpd[30920]: time reset +10.678548
Patrick> s Oct 18 17:29:58 client ntpd[30920]: synchronized to,
Patrick> stratum 1 Oct 18 17:31:59 client ntpd[30920]: no servers reachable

Patrick> ntpq -p says this: remote refid st t when poll reach delay offset
Patrick> jitter
Patrick> ==============================================================================
Patrick> grandfather.Sta .GPS.  1 u 49 64 375 0.243 2833.49 1139.84

grandfather is not sync'd - you will not be able to sync to it while it is
like this.

Patrick> For a while there was a * in the first column, but it went away.

For a while, that was good.  But then it was bad.

Patrick> Did I mention that there are several other clients with no problems
Patrick> at all?  ntpd 4.2.2 is running with -g, burst, and iburst.

Burst is probably not your friend.  There will also be pages on the support
web that will help with that, too.

Patrick> So, does this look like a hardware problem?  If not, I'll have to
Patrick> dig into networking and details of the configuration.

I recommend digging in to both HW and OS issues first.

And having more machines to sync with would also be useful.


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