[ntp:questions] ntpdate works, but ntpd doesn't (reach = 0)

Martin Burnicki martin.burnicki at meinberg.de
Tue Feb 10 11:37:07 UTC 2009


Uwe Klein wrote:
>>>If ntpd is restarted, it is Bad for the time to be stepped backwards for
>>>many people.  Since this could happen with -g, when restarting ntpd for
>>>this common case, one should not use -g.
> If you step forward the system effect will be comparable to "limbo"
> nothing has happened for an interval. we can live with that.
> ( Though cron,batch,at may stumble )
> If you step backward in time you are in danger of running into
> future timestamps.
> Think of a make in progress that sees timestamps for prerequisites
> as older than the target file due to the backward timestep.
> Unpleasantness ensuess.

I'm aware of the problems with stepping time backward, and I agree this
should be avoided.

The basic thing I don't understand in the context of this thread is why the
behaviour with -g should not become the default behaviour for ntpd. What if
the big difference if

a) ntpd without -g steps the time back by the amount of 128 ms up to the
sanity limit of about 1000 seconds

b) ntpd with -g steps the time back by the amount of 128 ms up to more than
the sanity limit

If backward time steps are Bad then also time steps below but maybe close to
1000 seconds are Bad. So there's basically no big difference if you use -g
or not.

Please remember this all is related to the statement that ntpd should not be
re-started (!) with -g, i.e. ntpd has already been running before, and thus
the system time has been synchronized before.

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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