Post #2958991
2026-03-26 15:54 UTC
Chrony and GPSd use shared memory to communicate, which requires the daemons to start in a specific order, otherwise they don't talk to eachother.
GPSd is supposed to send GPS on SHM0 (shared memory slot 0) and PPS on SHM1... which didn't work for me. I got GPS fine, but no PPS data. No idea why. GPSd definitely has PPS info, but wasn't sending it.
4/x
Replies (1)
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@rune@social.intothecloud.net 2026-03-26 15:54
I tried having Chrony use SHM0 for GPS, and reading the /dev/pps0 device directly for PPS... which would work fine for several hours, then PPS data would just randomly stop. Weird. Meanwhile, GPSd still has a running PPS feed. What finally worked for me was getting GPS via SHM0 from GPSd, and PPS via socket from GPSd. That has been stable for a couple days now. But that doesn't work if I "lock" PPS to GPS. Weird. 5/x