[ntp:questions] NTP makes a time jump

Larry Sheldon lfsheldon at gmail.com
Fri Jul 12 01:25:16 UTC 2013

On 7/11/2013 3:13 AM, Rob wrote:
> karpekin at gmail.com <karpekin at gmail.com> wrote:
>> Hello,
>> Clients indeed followed server after 2.5 hours.
>> This night they managed to come from -15s difference to +2.5s and now it seems trying to slew another direction. They will probably need another half a day to stop oscillations and finally come to zero. Pity I can't attach a trend picture here, looks pretty funny.
>> The only doubt I have is the initial 2.5 hours delay. Server rushed away from clients by ~8 seconds. Clients also moved away from each other a bit, but still max was 480 ms. So the system didn't make jumps but it broke apart for almost 12 hours.
>> Any advices how to make them all behave and be closer to each other?
> This happens because you do tests that the ntp daemon was not designed
> to withstand.

I wonder if he has ever documented his tests of use of a bicycle while 
deep-sea spear-fishing.

> We read it all the time on this newsgroup.  People want to install ntp
> and they have been asked to make a testplan and do tests.  They think
> about some stresstesting and draw a plan.  They pull plugs, set the time
> to incorrect value, connect again, restart the daemon, etc.  But that is
> not the environment that ntpd expects to be operating in, and in fact
> it performs very badly in it.
> So you need to decide: do I want to use ntpd and use it only within its
> expected operating environment (i.e. at most pull network plugs but do
> not disturb the clock in an unrealistic manner), or choose another ntp
> implementation that can withstand those tests (and may perform less well
> in day-to-day use).
> I hear about chrony all the time.  It should be better in correcting
> incorrect time quickly.  I never used it.
> But I know very well about the effects that you encounter with ntpd.
> Even "fiddling" with ntpd, changing the config file a couple of times
> and every time restarting the daemon, will heavily confuse it and you
> will see it moving AWAY from the correct time for a while.

Idioten aangeboden. Gratis af te halen.
h/t Dagelijkse Standaard

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