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

Martin Burnicki martin.burnicki at meinberg.de
Mon Feb 16 11:32:44 UTC 2009


Danny Mayer wrote:
> Martin Burnicki wrote:
>> Danny,
>> 
>> Danny Mayer wrote:
>>> Martin Burnicki wrote:
>>>> Of course synchronization will be better if ntpd reaches an upstream
>>>> server continuously, but still this is better than no synchronization
>>>> at all ...
>>>>
>>> No it wouldn't. That's a fallacy. ntpd already oversamples. This is all
>>> in the algorithms but sampling at the same rate provides no benefit and
>>> it is better off reducing the sampling frequency once it has a stable
>>> state.
>> 
>> What I meant is not to decrease the polling interval.
>> 
>> I meant to apply corrrections to the system time earlier. If you monitor
>> the offset in ntpq -p then you can see often it takes very long untio an
>> initial offset of a few milliseconds is started to be decreased.
> 
> Again this is all in the algorithms. You need to take care about when
> you apply the changes. ntpd tries to figure out whether or not a change
> is an aberration or real and then needs to try and make sure it does not
> overshoot. Don't forget you are getting values from a number of
> different servers and if you switch preference from one server to
> another you also end up potentially with perturbing the calculations.

If all the polling results indicate that the time is just off by a few
milliseconds then this should be compensated quickly.

I absolutely agree with Bill Unruh on this.

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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