[systemd-devel] Reloading configuration after mount unit

[Silvio Knizek]

Am Freitag, dem 18.06.2021 um 19:48 +0200 schrieb Norbert Lange:
> Am Fr., 18. Juni 2021 um 16:35 Uhr schrieb Silvio Knizek
<killermoehre at gmx.net>:
> >
> > Hi Norbert,
> >
> > make sure your /usr/local mount is done in the initrd and that you
use
> > »systemctl link /path/to/unit.service« to enable them.
> That's not really helping, I don't want to chug in tons of tools in
> the initramfs this is no desktop system.
> systemctl link shouldnt be necessary, as
/usr/local/lib/systemd/system
> is a standard unit path.

You're right with the path, I re-checked it.
For your initrd the general suggestion is to actually include systemd
in it. See https://systemd.io/INITRD_INTERFACE/ for everything.
>
> Since there is a systemd-update-done that changes /etc I would have
thought that
> systemd rereads the configuration (as /etc/systemd/system could have
> changed) during startup.
> I would want that for /usr/local/lib/systemd/system after this path
> was made available through a mount.
>
> 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.
>
> I dont know if thats the case or if I just dont know how (as
> systemd-update-done allows a changing /etc I would assume systemd
> would rescan it for units/dependencies)

systemds internal unit representation is actually static. Unit files
are only read when started as PID1 after the generators ran, while
switch-root'ing from the initrd and everytime you run »systemctl
daemon-re{load,exec}« (there are transient units as well, but this
would be to much for here).

What you could try is creating a new unit in /etc/systemd/system/
--- systemd-reload.service ---
[Unit]
Description=Reload systemd
Requires=usr-local.mount
After=usr-local.mount

[Service]
Type=oneshot
ExecStart=/usr/bin/systemctl --no-block daemon-reload

[Install]
WantedBy=usr-local.mount
---
and than a »systemctl daemon-reload && systemctl enable systemd-
reload.service«.
In theory (because completly untested) this unit should be activated as
soon as your /usr/local mount point is ready.
>
> >
> > For the automount behaviour, you need to add
> > »noauto,x-systemd.autmount,x-systemd.idle-timeout=10s«
> > to the options part in the /etc/fstab. See man:systemd.mount for
more
> > information.
>
> Thats Automount, but I want "LazyUnmount",
> and the suggestion kinda contradicts "make sure your /usr/local mount
> is done in the initrd"

The »x-systemd.idle-timeout=10s« actually unmounts the disk as soon as
10s long the disk is idle. Idle is defined as
- open file descriptors and
- process working directory.
So LazyUnmount (which you can define in an actual .mount unit) wouldn't
change anything IMHO.

(sorry for sending twice. Forgot the ML)