[ntp:questions] Change poll interval at runtime?

David Lord snews at lordynet.org
Sun Feb 26 10:27:28 UTC 2012


Ron Frazier (NTP) wrote:
> 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.

Minpoll 8 shouldn't cause servers any problem. Using
iburst sometimes gets rate limit responses from my own
servers when a client is restarted several times.

My own systems have been affected by temperature changes
this year and been stuck at faster poll rates than in
previous years but I don't know if that is due to it being
a warmer winter or different ntpd. Last week house was down
at 15C overnight up to 25C during day. Ntpd is now 4.2.6p5.


David



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