Re: [chrony-users] makestep examples in docs

[ Thread Index | Date Index | More Archives ]

It depends on what you want, and on how reliable your GPS receiver really is.
It might be great, or it might have glitches.

The first thing to do is to understand what was happening with your glitches.
Is it the gps or something else (eg some program on yuour machine which is
resetting the system clock). Make sure you have your logs operating
(especially the refclock, and the tracking logs). When you get one of those glitches, look in the refclock log if it was the gps
or your computer (look at the dates on the log lines which are obtained from
the system clock, and the offsets on the gps receipts. If you find that your system clock suddenly say it is Oct 15 2023. Also look
at the tracking around the same time.

How are you getting the gps time to chrony? Using gpsd? Using shm with some
other gps reading software, etc. Clearly using makestep will make things worse
if it is the gps reading that is the problem. On the other hand, if some other
program is messing with your system clock, then using makestep might well be
the right thing to do  (assuming you cannot get that other program to behave

William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 ____|____ and Gravity ______|_

On Fri, 29 Mar 2019, Brendan Simon (eTRIX) wrote:

I am using a GPS reference clock with chrony (on a Debian 8 Jessie system). 
Occasionally  the system time jumps way into the future and can screw up applications
that are sleeping or waiting based on wall system time.

I have been using `maxstep 1 -1`, assuming that the GPS time is always correct and steps
should always be made if out by more than 1 second.

That might be too extreme, so I want to only step in the first few updates, as suggested
by the docs.

The docs suggest `maxstep 0.1 3`, which would step if the error is greater than 100ms
for the first 3 (or updates).

That sounds ok, but every other example of `makestep` int the docs uses `maxstep 1.0 3`
(i.e. 1 second, not 100ms).  So is the 0.1 example a typo or is it intended.

In summary, would it be recommended to use `makestep 0.1 3` or `makestep 1.0 3` when
using chrony with GPS source (btw, it's the only source.  no ntp servers are used).

You could use either one. clearly the .1 will keep your system closer to the
GPS time. If the GPS time is wrong, then that is clearly not helpful.

Thanks, Brendan.

Mail converted by MHonArc 2.6.19+