[ntp:questions] Change poll interval at runtime?

A C agcarver+ntp at acarver.net
Sun Feb 26 23:29:51 UTC 2012


On 2/26/2012 15:09, Richard B. Gilbert wrote:
> On 2/26/2012 12:55 AM, Ron Frazier (NTP) wrote:
>> On 2/25/2012 5:05 PM, A C wrote:
>>> On 2/25/2012 13:09, Richard B. Gilbert 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.
>>>
>>> The idea was to bump up the minimum poll interval after ntpd has been
>>> running for a day or so to something more kind to the remote servers
>>> because the refclock is holding the remote servers clamped to 64
>>> seconds. If I set minpoll in the config file, then ntpd's start up
>>> takes a long time because of a long poll interval. If I don't set the
>>> minpoll, then ntpd doesn't do "a pretty good job" because it clamps
>>> the polling interval.
>>>
>>
>> I've noticed the same thing. You could try what I'm doing, although I'm
>> still testing for the best configuration.
>>
>> # GPS Lines
>> server 127.127.20.5 prefer minpoll 3 maxpoll 6 mode 72
>> fudge 127.127.20.5 time2 0.3100 refid GPS1
>>
>> # Internet server lines
>> # NIST New York
>> server nist1-ny.ustiming.org minpoll 8 maxpoll 13
>>
>> # other internet server lines similar
>>
>> Sincerely,
>>
>> Ron
>>
>>
> NTPD adjusts the poll interval dynamically. Just because MINPOLL=4 does
> not mean that the poll interval is "stuck" there. Give NTPD a
> rock solid 1 second per second source it will ramp up the poll interval
> to 1024 seconds. Those "rock solid" ticks can frequently be found
> 1:00AM to 5:00AM local time. The net quiets down and NTPD takes
> shameless advantage.
>
> If you really want good time and can afford a GPS *timing* receiver
> that's the way to do it. The last I heard, you could get a timing
> receiver for $100 -- $300.
>
> ANY GPS receiver knows what time it is but the navigation receivers
> give priority to location. Timing receivers give priority to delivering
> the correct time.
>

I have a timing receiver.  But after days of operation on a machine that 
does nothing but ntpd none of the Internet servers move up past 64 
seconds and the PPS stays put at whatever minpoll is even though I have 
no maxpoll.


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