[ntp:questions] Change poll interval at runtime?

unruh unruh at invalid.ca
Sat Feb 25 23:42:56 UTC 2012


On 2012-02-25, Richard B. Gilbert <rgilbert88 at comcast.net> wrote:
> On 2/25/2012 1:20 AM, A C wrote:
>> On 2/24/2012 21:26, A C wrote:
>>> Is it possible to change the polling interval of one or more associated
>>> servers at runtime? It seems like I should be able to run:
>>>
>>> ntpq -c "writevar &associd hpoll=N" or is it ppoll?
>>>
>>
>> Actually, I should have been more specific and say change the minimum
>> polling interval. In other words, be able to adjust the conf file's
>> minpoll flag at runtime instead of restarting.
>
> What problem are you trying to solve?
>
> NTPD does a pretty good job of adjusting itself most of the time.
>
> Short poll intervals are useful when correcting large errors.
> Long poll intervals allow NTPD to make small corrections very accurately.

IF the drift is very stable, long poll intervals allow ntpd to make
small corrections to the drift rate accurately. They in general make the
offsets larger and mean that the system cannot respond to changes (eg
temp changes due to the coputer being used) rapidly. This is especially
true of ntpd because it throws away 7/8 of the measurements in the clock
filter, meaning that the actuall poll time is about 8 times longer than
the set poll interval. (poll 10 then has an effective poll of 8000 sec)

Anyway, that is an aside. I agree with you that I do not understand what
problem he is trying to solve. 


>



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