[ntp:questions] Can a clock drift be too big for ntpd?
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: synchronized to 220.127.116.11,
Patrick> stratum 1 Oct 18 17:27:48 client ntpd: no servers reachable
Patrick> Oct 18 17:29:06 client ntpd: synchronized to 18.104.22.168,
Patrick> stratum 1 Oct 18 17:29:16 client ntpd: time reset +10.678548
Patrick> s Oct 18 17:29:58 client ntpd: synchronized to 22.214.171.124,
Patrick> stratum 1 Oct 18 17:31:59 client ntpd: no servers reachable
Patrick> ntpq -p says this: remote refid st t when poll reach delay offset
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
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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