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

Lars Ericsson laeatwork at gmail.com
Wed Jul 13 20:31:50 UTC 2011

Thanks for the reply.

>> I recently run into a strange behavior where our communication software
>> failed on some critical timeouts.
>> After some investigation we found out the the system time suddenly made a
>> jump with 200ms.
> Yup. ntpd makes huge statements about the importance of keeping things
> monotonic, and then makes jumps if the time is more than 125ms out. Now,
> usually that indicates that there is something wrong with the system
> clock, so you should check it out.

What could be wrong with the system clock ?

> This is especdially true if the
> system has been running for a while and then jumps. It could also be
> that the servers you have are inconsistant, and out from each otehr by
> some large amount and you have too few servers for ntp to figure out
> which are giving good time.

More likely the source of the problem.

>> My question is: How do I prevent NTP clock adjustments from jumping. OK, it
>> will take some time to adjust but that's OK.
> a)Run chrony. ntpd will only use a max of 500PPM rate adjustment. Chrony
> can go up to 100000PPM to adjust away a large time discrepancy.

The problem is that the adjustment takes to large steps, not that it
takes to long time.

> b) Find out why your clock is suddenly finding itself out by that huge
> amount.

I'm working on it ;)


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