[ntp:questions] testing slew only mode (-x), not slewing correctly (linux sles10, ntpd v 4.1.1)

JohnLund jlund69 at gmail.com
Mon Oct 19 20:48:31 UTC 2009


I am trying to test the slew only mode of ntpd on an embedded system
that has ntpd v. 4.1.1.  We cause a time jump of 1 minute on the
configured NTP server for this embedded system and track the ntp log
messages (var/log/ntp) and see the following:
19 Oct 17:53:47 ntpd[6951]: time slew 51.517400 s
19 Oct 18:08:53 ntpd[6951]: time slew 51.517509 s
19 Oct 18:24:51 ntpd[6951]: time slew 51.517592 s
19 Oct 18:39:57 ntpd[6951]: time slew 51.517755 s
19 Oct 18:54:59 ntpd[6951]: time slew 51.517882 s
19 Oct 19:10:01 ntpd[6951]: time slew 51.517964 s
19 Oct 19:26:04 ntpd[6951]: time slew 51.518076 s
19 Oct 19:41:10 ntpd[6951]: time slew 51.518088 s
19 Oct 19:56:11 ntpd[6951]: time slew 51.518059 s
19 Oct 20:11:16 ntpd[6951]: time slew 51.518151 s

If slewing were working I would think that the "time slew" shown in
the log file would be continuously decreasing.  Instead it seems to be
unpredictably increasing (and decreasing at times), as if this mode
were unstable.  I looked in the systems /var/log/messages file to see
if there are any system messages about the clock, and only see the
changes from running ntpdate at startup to set the system time from
the configured NTP server (before the time jump).

Also it looks like the drift/frequency is set to a large negative
number by ntpd, when it would seem logical with a large positive time
jump that the frequency should be changed to a large positive number
in order to slew toward correct time.

[root at c007n01 ~]# ntpq -c readvar
assID=0 status=06d4 leap_none, sync_ntp, 13 events, event_peer/
strat_chg,
version="ntpd 4.1.1 at 1.786 Sat Sep 27 05:48:59 UTC 2003 (1)"?,
processor="i686",
system="Linux2.6.16-SLES10-66141cc95035c9ccdd2c2f14e637f60e-0.8",
leap=00, stratum=6, precision=-18, rootdelay=0.273,
rootdispersion=32.972, peer=41813, refid=10.241.58.159,
reftime=ce8750b1.a00bed74  Mon, Oct 19 2009 20:55:13.625, poll=6,
clock=0xce8750ca.3c4b2b77, state=3, offset=51518.340,
frequency=-497.407, jitter=0.018, stability=337.594


I'd like to figure out why the time slew is not working with the -x
option.  Is there some other logging that I can turn on, or another
log file I can look at to see if there is a reason the time
adjustments are not being done correctly?




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