[systemd-devel] Q: daemon-reload: when and how?

[Simon McVittie]

On Thu, 18 Jun 2020 at 11:01:59 +0200, Jérémy ROSEN wrote:
> multiple unit files need to work together to make a working environment, and
> systemd can't know when all changes are consistent and
> it is safe to reload. So systemd will want an explicit order from the user.

Also, reloading is disruptive and can be "expensive" in terms of resource
use. If you're making a lot of changes (like an upgrade transaction in
a package manager like apt or RPM), you probably want to do the entire
transaction, and then reload *once*.

dbus-daemon *does* automatically reload when configuration or service files
change. People now expect/rely on this, so it's undesirable to change,
but with hindsight I wish it didn't. I think the fact that systemd *doesn't*
automatically reload is partly learning from dbus-daemon's mistake.

On Thu, 18 Jun 2020 at 12:43:59 +0200, Ulrich Windl wrote:
> Is there something like "systemd suggests daemon-reload" (assuming systemd
> detects the situation, but does not issue a reload itself)?

Yes there is:

$ systemctl status dbus.service
(... some information here ...)
$ sudo touch /lib/systemd/system/dbus.service
$ systemctl status dbus.service
Warning: The unit file, source configuration file or drop-ins of
dbus.service changed on disk. Run 'systemctl daemon-reload' to reload
units.
(... same status information ...)

In this case I didn't really alter /lib/systemd/system/dbus.service,
just changed its mtime, but you'd get the same thing from an edit that
actually matters.

    smcv