[systemd-devel] Reloading configuration after mount unit

[Uoti Urpala]

On Fri, 2021-06-18 at 19:48 +0200, Norbert Lange wrote:
> If systemd assumes the whole /usr drive to be static and has no way to
> dynamically reload and "retarget"
> (adding new wants/requires dependencies to starting/started targets)
> then I guess that's the end of it.

Systemd does not necessarily assume the whole of /usr to be mounted at
once - you could have binaries and data in submounts and systemd could
wait for those - but there is no "normal" way to add units in the
middle of operation. There is "daemon-reload", but it's more meant for
things like online updates, not part of a standard boot sequence.
Normally the complete set of units to start in a boot should be known
early, not appended to in parts as things are mounted.

So you could have tools in a separately-mounted /usr/local, but I think
you'd need to have the systemd configuration for them in the main /usr
to have things behave nicely.