Re: [chrony-users] Time synchronisation over a high-latency packet radio network

[Stuart Longland <stuartl@xxxxxxxxxxxxxxxxxx>]

On 8/5/19 1:30 am, Lonnie Abelbeck wrote:
> Just curious, it appears you have native DNS, why do you need to proxy NTP over APRS (unless you use a similar technique for DNS).

Ahh, because I actually do not have DNS at all.  Not when the devices
are out in the field. :-)

The only time I have DNS is when I plug a USB cable into the
PocketBeagle that connects to a computer with an Internet connection.

Then, I can skip the packet radio stuff and go direct over the
CDC-Ethernet gadget that the PocketBeagle sets up.  So when developing
at home, I just need to set /etc/resolv.conf, add a route to 0.0.0.0 and
hey presto, I can hit real NTP servers direct.

I can't do this in the field because the computer I might plug this box
into won't have an Internet connection either and the whole point of the
exercise was to avoid having to have a laptop at check-points.  (The
laptop should be completely optional and should not need to have a NTP
server installed.)

> BTW, at startup our project always steps the time using (8 second timeout would be too low for you):
> --
> chronyd -q -t 8 "server time.example.tld iburst"
> --
> before starting "chronyd" in the background. (no systemd).

That could be a solution too, I think I tried iburst and found that was
a big no no on packet because each NTP message took about 2 seconds to
send (let alone receive a reply) and iburst just blasted the requests
out so damn fast the 1200 baud radio link couldn't keep up.

That said, it's a useful starting point, and maybe a `cron` job can look
for the "magic" system time that says "I don't actually know what the
time is", and run a variation of that command.  Perhaps drop the iburst
and raise the time-out to maybe 30 seconds.  (Ohh, and set the port number!)

We don't need millisecond precision right up front: just to be within a
minute.  `chronyd` can then fine tune it from there. :-)

Regards,
-- 
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
  ...it's backed up on a tape somewhere.

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