[RndTbl] strange NTP problem on one of 3 peers
Gilles Detillieux
grdetil at scrc.umanitoba.ca
Wed Apr 25 11:56:51 CDT 2012
On 04/25/2012 11:03 AM, Gilbert E. Detillieux wrote:
> Are you sure ntpd is running on all systems? Try running the following
> command, on each of your systems:
>
> /usr/sbin/ntpq -p
>
> This will tell you not only whether ntpd is running, but also where each
> one is getting its clock settings from, what the drift is, etc.
>
> Note that if the initial clock setting is too far out of whack, ntpd may
> not even start properly. It's usually useful to run ntpdate first, to at
> least start off with a close-to-synchronized clock. For some reason,
> RHEL systems don't do that by default even when you enable ntpd.
I ran that on all 3 systems, and it shows ntpd is indeed running on all.
SL 5 does seem to run ntpdate first, before starting ntpd, to get the
clock sync'ed up beforehand, as long as you have systems defined in
/etc/ntp/step-tickers or you put a -x in OPTIONS in /etc/sysconfig/ntpd.
But I wonder if there are some NTP servers on the net that are out of
whack. When I run ntpq, the system that has the drift (cliff) shows
different results than the other two:
On cliff:
remote refid st t when poll reach delay offset
jitter
==============================================================================
caustique.anox. 209.51.161.238 2 u 5 64 73 35.302 32.315
4564.06
tb.mircx.com 64.90.182.55 2 u 2 64 77 46.530 72.637
4517.32
cliff.scrc.uman .INIT. 16 u - 64 0 0.000 0.000
0.000
larry.scrc.uman 208.80.96.70 3 u 16 64 76 0.001 6019.84
3675.39
dave2.scrc.uman 209.167.68.100 3 u 4 64 42 0.001 6140.53
3858.45
*LOCAL(0) .LOCL. 10 l 2 64 77 0.000 0.000
0.001
On larry:
remote refid st t when poll reach delay offset
jitter
==============================================================================
+zeus.yocum.org 131.188.3.220 2 u 148 256 377 35.330 -2.723
3.170
*ellen.linuxgene 142.3.100.2 2 u 214 256 377 31.665 -1.240
2.296
cliff.scrc.uman .INIT. 16 u 17 64 0 27.461 -87882.
0.000
larry.scrc.uman .INIT. 16 u - 1024 0 0.000 0.000
0.000
+dave2.scrc.uman 209.167.68.100 3 u 204 256 377 0.400 2.594
0.890
LOCAL(0) .LOCL. 10 l 44 64 377 0.000 0.000
0.001
dave2's results are similar to larry's.
A few other things I thought I should point out: All 3 systems have
ports 123/tcp and 123/udp open in iptables. The clock on cliff seems to
drift whether or not ntpd is running, though that could be because the
calculated drift compensation is out of whack. The /var/lib/ntp/drift
file on cliff hasn't been modified since 1:58 this morning, before the
reboot, while it has been on the other 2 systems. All 3 systems have an
identical configuration, using 0.pool.ntp.org as the step-ticker, and
0.pool.ntp.org and 1.pool.ntp.org as stratum 1 servers.
--
Gilles R. Detillieux E-mail: <grdetil at scrc.umanitoba.ca>
Spinal Cord Research Centre WWW: http://www.scrc.umanitoba.ca/
Dept. Physiology, U. of Manitoba Winnipeg, MB R3E 0J9 (Canada)
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