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I've got ntpd running. It's been running for a while, and the polling frequency is up to the max of 1024

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*time.local      132.163.4.102    2 u  813 1024  377    0.109   -0.209   0.342

For whatever reason, I would like to set the polling frequency back to 128 sec. I don't mind if, after it does 128 sec for a while, it follows its usual plan of increasing the poll frequency back to 1024. But right now, at this moment, I want it at 128.

Is there a way to do that? The only way I know is to restart ntpd.

hymie
  • 1,276

3 Answers3

1

Yes - but you will need to restart ntpd to reload the config.

Have a look at the docs here.

You can set two options minpoll n and maxpoll n which you can adjust to give you the desired upper and lower limits.

These options specify the minimum and maximum poll intervals for NTP messages, in seconds to the power of two. The maximum poll interval defaults to 10 (1,024 s), but can be increased by the maxpoll option to an upper limit of 17 (36.4 h). The minimum poll interval defaults to 6 (64 s), but can be decreased by the minpoll option to a lower limit of 4 (16 s).

For example in my config I list;

server 127.127.28.1 minpoll 4 which polls my gps pps every 16sec.

minpoll & maxpoll cal be used together.

I don't believe there is any way to reduce the poll frequency 'now' and have it work back up to 1024 but you can reduce it and keep it within a more desired window.

user3788685
  • 567
0

It would be theoretically possible if you had configured authentication keys ahead of time in /etc/ntp.conf, found the association id with ntpq, and used the writevar command on the association id to change the polling interval.

Except that the only association variable you're allowed to change at runtime is the leap second indicator. See https://lists.ntp.org/pipermail/questions/2005-February/004382.html for an explanation of this and a pointer to the code that implements it.

In short, no it's not possible. Why do you think you want to change the polling interval anyway?

Paul Gear
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The alternative to restarting ntpd is to reconfigure the time server association, using the ntpq utility to drop the old server and re-add it with the new configuration. Just as in /etc/ntp.conf, arguments to the server command establish the new polling interval.

Here is a made-up session transcript that illustrates:

# ntpq
ntpq> apeer
     remote       refid   assoc  st t when poll
=============================================== ...
*time.local      caffe17e 07734   2 u  813 1024
ntpq> :config unpeer 07734
Keyid: 23
MD5 Password: haileris
Config Succeeded
ntpq> :config server time.local minpoll 7 maxpoll 7
Config Succeeded
ntpq> apeer
     remote       refid   assoc  st t when poll
=============================================== ...
*time.local      caffe17e 07735   2 u   10  128
ntpq> quit
#

(You can see in the transcript that the :config command prompts you to authenticate yourself to your server. If you haven't already set up an authentication key for this purpose, then you'll need to do that first. That's out of scope of this question, but in a nutshell means editing /etc/ntp.keys and /etc/ntp.conf, followed by a one-time restart of ntpd to load the authentication settings.)

I verified this works on my system, which runs version 4.2.8p15 of the NTP reference implementation.

MetaEd
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