[systemd-devel] alternative approach to waiting for system time to be set

[Peter A. Bigot]

Like others I'd like to use systemd to defer starting a service until 
the system time has been set accurately.  Previous approaches to 
resolving issue #5097 don't seem to be going anywhere.

https://github.com/pabigot/timesyncwait has my proposed solution: a 
standalone service that blocks until adjtimex(2) confirms that something 
has told the kernel its realtime clock is synchronized. It also provides 
a new time-synchronized.target so it can be installed alongside an 
unmodified timesyncd.

Initial tests show this meets my needs.  I'd be willing to rework it as 
a patch to systemd if there's consensus the approach is reasonable.

Peter

Mar 15 17:14:17 raspberrypi3 systemd[1]: Starting Wait Until Kernel Time 
Synchronized...
Mar 15 17:14:17 raspberrypi3 timesyncwait[107]: adjtime state 5 status 
40 time 1521134057.408590
Mar 19 01:04:35 raspberrypi3 timesyncwait[107]: adjtime state 0 status 
2000 time 1521421475.316852
Mar 19 01:04:35 raspberrypi3 systemd[1]: Started Wait Until Kernel Time 
Synchronized.

References:
* https://github.com/systemd/systemd/issues/5097
* https://github.com/LukeShu/systemd-timesyncd-wait
* 
https://lists.freedesktop.org/archives/systemd-devel/2014-November/025131.html
* https://lists.freedesktop.org/archives/systemd-devel/2017-May/038952.html