[ntp:questions] Change poll interval at runtime?

unruh unruh at invalid.ca
Mon Feb 27 01:11:48 UTC 2012

On 2012-02-26, A C <agcarver+ntp at acarver.net> wrote:
> 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 prefer minpoll 3 maxpoll 6 mode 72
>>> fudge 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.

The PPS is supposed to stay at 16 seconds poll interval. It is not
supposed to move up in poll interval.  Why your others
are not moving up I do not know. 

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