[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)


More information about the Roundtable mailing list