[ntp:questions] Time slew doesn't seem to work

jkvbe jkvbe at yahoo.com
Mon Apr 14 10:53:31 UTC 2008

On Apr 9, 4:40 pm, andy.heltenNOS... at dot21rts.com (Andy) wrote:

> Two things:
> (1)  Try running with time stepping enabled on that system (i.e. don't
> use the '-x' flag) to see how well the system keeps time.  What kind of
> offset do you have after 1 or 2 hours of operation?
> (2)  Check your drift value when running with time stepping disabled
> (also check it with time stepping enabled).  You can do this with 'ntpq
> -crv' where 'frequency' is the drift value or you can dump the drift
> file (probably /var/lib/ntp/drift).  Note that the drift file is only
> updated once every hour or so.
> I encountered a problem on linux 2.6.18 in which disabling of time
> stepping (using either '-x' or 'tinker step 0') caused the drift value
> to run at or near +/-500ppm and subsequently caused a time offset of
> several milliseconds.  If I allow time steps on that same system, it
> runs with a drift <100ppm and maintains an offset <1ms.  I am using an
> IRIG time source, so I expect high accuracy.  In my system, a time step
> is never needed (i.e. the offset never grows larger than 128ms),
> regardless of whether time stepping is enabled or disabled.  This
> doesn't change the fact that it runs like crap with time stepping disabled.
> Andy

Note that the my set-up was an experiment to check how time slew
worked. What I still don't get is why it works when using ntpdate.
Also strange is the fact that ntpq actually reports the node as
synched with an offset of > 1.6s.


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