Hi, I am no expert, but I just set it up on my own network and from what I understand of OpenNTPD's design, the daemon doesn't "select" the best source to follow it exclusively. Instead, it calculates a median from all valid sources to adjust the clock.
Even if your sensor has a high weight, the network servers are still included in this calculation. Their 1-2ms jitter is factored in, which "pulls" the system's offset away from the microsecond precision of your sensor. It seems to be a design choice: OpenNTPD prioritizes a stable median (security/stability) over the absolute precision of a single source. Hope this helps. Kevin Le mer. 31 déc. 2025, 16:27, Maurice Janssen <[email protected]> a écrit : > Hi, > > I have a couple of small machines (Soekris 6501 and 5501) that I use as > NTP server in the NTP pool. > When I use a sensor as the only source of time (Garmin 18lvc on the serial > port or Meinberg PZF180PEX DCF77 receiver card), the offset is quite good: > nearly allways below 20 us, most of the time below 5 us and sometimes even > less than 1 us. > But when I add another server (mainly as backup in case the sensor doen't > work), the offset drifts away to 1 or 2 ms. I tried with 1 sensor and > 1 server, with 1 sensor and multiple servers, I tried adding weight 5 or 10 > to the sensor, but this doesn't seem to have any effect. In all cases ntpd > stays synchronised to the sensor (with poll=15s), but after an hour or so > after starting ntpd the offset starts to increase. And from that moment, > the > offset wanders between roughly -2 and +2 ms. > It almost seems as if ntpd is synchronised with one of the servers (with > much higher polling interval), however ntpctl still shows that it is > synchronised to the sensor (albeit with the wandering offset as described > above). > > I would prefer to have the microsecond offset _and_ some servers as backup, > but can't get it working like that. > > Am I missing something? Or is this a bug in ntpd? > > Thanks for any help. > >
