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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Subject: Re: [chrony-users] Chrony gets out of sync regularly
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Mon, 7 Mar 2022 12:36:29 +0100
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On Thu, Mar 03, 2022 at 10:03:54PM -0600, Steven Sommars wrote:
> Config: Host sync'd to nearby stratum 1s. Jitter ~35 usec. gpsd 3.23
> gpspipe, gpspipe -R and ntpshmmon running simultaneously for several hours
>
> gpspipe -T '%s' --usec -r | sed 's|,.*||'
> Min Max
> (sec) (sec)
> .132419 .168017 GPGBS
> .132332 .167903 GPGGA
> .132393 .167985 GPGSA
> .389284 .549959 GPGSV
> .132364 .167938 GPRMC
> .132263 .167829 GPZDA
I think that indicates the timing of GPGSV messages somehow
impacts the SHM timestamping. That would be a bug in gpsd.
> >>> Why do you need the SHM 0? You can use SHM 1 or SOCK.
> Some cookbooks (e.g.,
> https://support.ntp.org/bin/view/Support/ConfiguringSHMRefclocks ) use both
> SHM 0 and SHM 1
That might had been necessary with very old versions of gpsd (IIRC it
originally required something to bring the system clock close to the
PPS before it locked), but with more recent gpsd versions the
configuration should be one of the following:
1) refclock SOCK
2) refclock SHM 1
3) refclock SHM 0 noselect + refclock PPS lock SHM0
I don't recommend using SHM 0 and SHM 1 at the same time. Typically,
SHM0 is worse than a remote NTP server and makes falseticker detection
less reliable.
--
Miroslav Lichvar
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