[ntp:questions] How to get shared memory access from gpsd to ntpd to work?

Etaoin Shrdlu etaoin at clickworkorange.com
Fri Aug 18 11:33:48 UTC 2017

Hi guys, 

Thanks a million for getting back to me on this, really appreaciate it!

On Wed, 2017-08-16 at 13:40 -0700, Gary E. Miller wrote:
> Yo Etaoin!
> On Wed, 16 Aug 2017 13:52:44 +0100
> Etaoin Shrdlu <etaoin at clickworkorange.com> wrote:
> > 
> > P.S. This has been cross-posted from gpsd-users at nongnu.org, where I
> > failed to get any response to my query. 
> I never saw it there.  I just sent a test message to that list and
> the
> list is working fine.

Odd, it's in the list archive: http://lists.nongnu.org/archive/html/gps

> It looks like the time is not getting from gpsd to ntpd.  The test
> that shows the link between gpsd and ntp over shm is ntpshmmon, part
> of the gpsd pacakge.. Just run that and see what you get:
> It should look like this:
> # ntpshmmon
> ntpshmmon version 1
> #      Name
> Seen@                Clock                Real                 L Prec
> sample NTP0 1502915839.595703946 1502915839.583110543
> 1502915839.703999996 0 -20
> sample NTP1 1502915840.000040002 1502915840.000014822
> 1502915840.000000000 0 -30
> sample NTP0 1502915840.603454013 1502915840.603269997
> 1502915840.703999996 0 -20
> sample NTP1 1502915841.000099871 1502915840.999982405
> 1502915841.000000000 0 -30

On Thu, 2017-08-17 at 07:11 +0200, Miroslav Lichvar wrote:
> There is a ntpshmmon program included with gpsd, which should show
> you if gpsd is actually writing to the SHM segments and whether it's
> a problem on the gpsd or ntpd side. However, I'm not sure if this is
> supposed to work with GPS over network.

I had to build the gpsd clients manually since this is a headless
system, and the package in the repo depends on X (due to it including
some Gnome apps), but I got them now and you're right ntpshmmon returns

/gpsd-3.16# ./ntpshmmon
ntpshmmon version 1
#      Name   Seen@                Clock                Real               L Prec

> Also, how are you starting gpsd and ntpd?
> I do not know anyone using GPS over udp...

I tested starting gpsd manually in a root terminal with 

# gpsd -N udp://

But it makes no difference. gpsmon still works though, so I don't think there's an issue with gpsd getting its data via UDP. More likely to have something to do with shm permissions, but I've never dealt with this before so I'm a little lost... 



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