State of the microserver HOWTO

Gary E. Miller gem at
Tue Jun 7 00:06:57 UTC 2016

Yo Eric!

On Mon, 6 Jun 2016 19:54:22 -0400
"Eric S. Raymond" <esr at> wrote:

> 1. How does ordering the refclocks in that way reduce startup
> glitches? As written this is a maddening, uninformative tease
> equivalent to mumbling "magic happens here".  Please reply via a
> config with a better header comment.

As recently discussed on devel at
But let me take a stab at it.

"On startup ntpd will take the first time it gets to set the system clock.
If this first time is an imprecise clock, say derived from NMEA, then
ntpd may takes days to restabilize.

The first time ntpd acquires will tend to be the ones higher up in the
file with the lowest maxpoll.

So to work around this ntpd glitch put your best time sources high in
the ntp.conf file, with your shortest maxpoll and your worst one at the
bottom with higher maxpolls."

> 2. What has maxpoll got to do with ARP delays? See above...

As recently discussed on devel at
But let me take a stab at it.

"The default APR timeout on Cisco switch gear may be as long as
4 hours.  On windows and Linux it may be as short as 60 seconds.

If the polling interval for a chimer is greater than 60 seconds (maxpoll 6+)
then when ntpd sends a time request to a remote ntpd daemon the OS may
be adding an ARP roundtrip to the process, delaying the return
by that much extra time.  This convinces ntpd that the remote ntpd
is further away, and has more jitter, than it actually does.

To prevent this glitch in ntpd behavior, be sure to use 'maxpoll 4' or
'maxpoll 5' on local servers and peers."

> I guess I should remark that right now I'm not very interested in
> logging or security directives.

You should be.  I'm fascinated with the graphs ddrown's scripts are
ginving me.

> If we need to add a section on those
> we will, but they're orthogonal to what really mattee for these
> examples, which is *how to configure clocks*.

What good is a refclock if you do not know 'how good' or have the data
to debug it.

You can include the logging statements with the comment:

# You want this logging, it will be usefull later.

If you add the logging early, then you have the data when you figure
out you want it.  If you wait until you want it then it is too late.

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