On Sun, Aug 07, 2016 at 10:27:02PM -0400, Chris Greenman wrote:
> I've attached the strace files.   The commands I used were:
> 
> root@IrishMistII:/tmp# strace -o /tmp/chrony.strace.out chronyd
> root@IrishMistII:/tmp# strace -o /tmp/gpsd.strace.out gpsd -D 8 -F
> /var/run/chrony.ttyACM0.sock /dev/ttyACM0

The -F option of gpsd is for its control socket. It's not related to
the chrony socket. Also, I think gpsd uses the chrony socket only for
samples based on PPS signal, so if you don't have working PPS, you'll
probably need to stick with SHM.

The problem is most likely one of the following:
1) gpsd is not writing to SHM
2) chronyd is not reading from SMH
3) chronyd is ignoring SHM samples (e.g. when the receive timestamp is
   from future)

Output from "gpsd -D 8" should confirm it's not 1). For 2) and 3) it
would be best to see "chronyd -d -d" output, but this will work only
if chronyd was compiled with debugging support (configure has
--enable-debug option since chrony-1.30).

Recent gpsd releases include a ntpshmmon tool, which can print changes
in the SHM segment and could be useful to reject 1) and 2).

-- 
Miroslav Lichvar

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