TIL that systemd-timesyncd is NOT a time synchronising service. It doesn't run NTP, it doesn't "synchronise" the clock.
It runs SNTP and jumps the clock to whatever it finds.
Add this to the list.
@yojimbo Man page claims that it does slew the time for "smaller deltas". This makes me confused: why is the threshold for smaller not configurable? That would probably be at least significantly helpful, and seems a total nobrainer. Similarly distinguishing between "first sync after boot" and "everything that's done after time-set.target/time-sync.target is considered up".
I would also expect that you'd prefer a possibly discontinuous time sync during boot to slewing time from a clock that's set incorrectly by more than a day. Or is there some other behaviour that you'd want in this case?
