[ntp:questions] How do I prevent sudden system time jumps.

Miroslav Lichvar mlichvar at redhat.com
Thu Jul 14 10:11:28 UTC 2011

On Wed, Jul 13, 2011 at 04:49:37PM -0500, Hal Murray wrote:
> >The problem is that the adjustment takes to large steps, not that it
> >takes to long time.
> ntpd will slew the clock at 500 PPM.  You may be willing to wait a while
> for a second or two, but it takes a looooong time if you have to adjust
> by several minutes or an hour.  That may be OK for your setup, but you
> should think about it.
> If you are using the -x flag, be sure to check out the -g flag that will
> let it do one long jump at startup time.

The -g option only allows the initial offset correction to be larger
than 1000 seconds, it doesn't affect the step value.

When both -x and -g are used and the initial offset is just below 600
seconds (-x is alias for "tinker step 600"), it will still take about
two weeks to correct the offset.

An interesting scenario is when tinker step is larger than panic and
the initial offset is between the two. With -g the first clock update
is allowed, but the clock is not stepped so the following updates will
still be be over the panic limit and ntpd will abort.

Miroslav Lichvar

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