When initializing a system (e.g. first boot / livecd) we have no good
reference source for time. systemd-timesyncd however would revert back
to its configured fallback time (in our case 01.01.1980). Since we
probably don't want to hardcode a specific date as fallback we are now
using the current system time (wherever that might have come from) to
initialize the reference clock file.
The only systems that might be remotely affected by this change are
machines that have highly unreliable RTCs or those where the battery
that backs the RTC is running empty.
Historically these systems always had a tough time with anything time
related and likely required manual intervention.
For stateless systems (those that wipe / between reboots or our
installer CDs) this has the consequence that time will always be reset
to whatever the system comes up with on boot. This is likely the correct
time coming from an RTC. No harm done here the situation is likely
unchanged for them.
For stateful systems (those that retain the / partition across reboots)
there shouldn't be a change at all. They'll provide an initial clock
value once on their lifetime (during first boot / after installation).
From then onwards systemd-timesyncd will update the file with the newer
fallback time (that will be picked up on the next boot).
Upstream has this alias too; so that dbus activation works.
What I don't fully understand is why this would ever be useful given
this unit is already started way in early boot; even before dbus is up.
But lets just keep behaviour similar to upstream and then ask these
questions to upstream.
This adds an `extraConfig` option to timesyncd for setting additional
options in `/etc/systemd/timesyncd.conf`.
This is similar to things like `services.journald.extraConfig` and
`services.logind.extraConfig`.
Somewhen between systemd v239 and v242 upstream decided to no longer run
a few system services with `DyanmicUser=1` but failed to provide a
migration path for all the state those services left behind.
For the case of systemd-timesync the state has to be moved from
/var/lib/private/systemd/timesync to /var/lib/systemd/timesync if
/var/lib/systemd/timesync is currently a symlink.
We only do this if the stateVersion is still below 19.09 to avoid
starting to have an ever growing activation script for (then) ancient
systemd migrations that are no longer required.
See https://github.com/systemd/systemd/issues/12131 for details about
the missing migration path and related discussion.
- most nixos user only require time synchronisation,
while ntpd implements a battery-included ntp server (1,215 LOCs of C-Code vs 64,302)
- timesyncd support ntp server per interface (if configured through dhcp for instance)
- timesyncd is already included in the systemd package, switching to it would
save a little disk space (1,5M)
Otherwise, the enabled -> disabled transition won't be handled
correctly (switch-to-configuration currently assumes that if a unit is
running and exists, it should be restarted).
