[ntp:questions] Change poll interval at runtime?

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sun Feb 26 05:20:16 UTC 2012

On 2/25/2012 6:42 PM, unruh wrote:
> 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.

I'll admit to not having read every sentence in this thread, but I have 
a question about what was just said.  Even if the clock algorithm 
discards 7/8 of the measurements, as stated, isn't ntpd sitll hitting 
the remote servers at whatever the minpoll value is set to, or the 
default minpoll value if not set.  So, if the internet servers are set 
to a minpoll value of 8 (approximately 4 minutes), aren't those remote 
servers actually getting polled every 4 minutes, regardless of what ntpd 
does with the data.




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Ron Frazier
timekeepingdude AT c3energy.com

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