copied from gpsd users list

Paul Theodoropoulos paul at
Thu Mar 19 22:00:36 UTC 2020

It's more relevant here. However, it wouldn't surprise me if every single 
person on this list is already subscribed to gpsd-users. Heh.

 From Gary E. Miller <gem at>:

Yo Paul!

On Thu, 19 Mar 2020 13:50:32 -0700
Paul Theodoropoulos via<gpsd-users at>  wrote:

>> The problem at hand is that a user has local PPS and wants that time
>> to win the startup race, ahead of the more jumpy network chimmers.
>> It is maybe 1,000x more accurate and stable.
>> To that end, a user places the PPS at the top of the ntp.conf, with
>> a short poll time than other refclocks, so that ntpd will select it
>> first.
>> But, when you add in a bunch of marginal pool servers, from all over
>> the planet, and iburst them, then they win the race instead of the
>> nice local PPS.  ntpd starts out with the worst refclocks, not the
>> best.
>> Eventually ntpd will sort it out, usually, but best to just pick the
>> local PPS on startup.
> So, if I may interject for my own clarity. For an ntp server with a
> properly running GPS and PPS, in a stable environment with reliable
> network, this would suggest that - regardless of pool*or*  peer - it
> is best not to use iburst?

That would be my suggestion if normal startup quality is important to you.
I can see a corner case where your PPS/GPS is dead, and you are still
in a hurry to start.  But even that is minimal if you have a good RTC.

Since most people only very rarely restart their stratum 1, not a big


> As in, iburst is desireable for_client_  ntp devices, not for those
> that are themselves stratum one?

That would be a good rule of thumb.

> (I'd like to copy this and its answer to the ntpsec list, since it's
> most relevant there, if permissible)

Yeah, this whole discussion really belong there.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at   Tel:+1  541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
     "If you can't measure it, you can't improve it." - Lord Kelvin

Paul Theodoropoulos

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