[systemd-devel] Generators, Targets and Stater Units - I am holding it wrong?

[Marc Haber]

Hi Lennart,

thank you for trying to help. tl;dr setting the symlinks accomplishes 
the intended behavior.

On Mon, Jun 23, 2025 at 01:27:24PM +0200, Lennart Poettering wrote:
>On So, 22.06.25 22:30, Marc Haber (mh+systemd-devel at zugschlus.de) wrote:
>I am not sure I follow. What are you trying to do? Do you want that
>the service units you generated are automatically activated at boot
>without any further admin step?

Yes. The admin step is putting the configuration into the file that the 
generator reads. It is a reimplementation of my first Debian package, 
console-log, leveraging systemd's flexibility instead of putting 
everything in an initscript on steroids (that was back in 2000) that 
allows you to have a less syslog on tty9 and a less maillog on tty8, for 
example.

>Or do you want that there's an
>explicit enablement step the user has to do via "systemctl enable"?

No.

>If you do not want that extra step, then just do create a symlink from
>the service units you generate (which you generate into one of the
>thre params that a generator gets passed via argv[], let's call the
>one you picked $TARGET) to the multi-user.target.wants/ subdir.
>
>i.e. add something like this to your generator code:
>
>    mkdir -p $TARGET/multi-user.target.wants
>    ln -s ../console-log-8.service $TARGET/multi-user.target.wants/console-log-8.service
>    ln -s ../console-log-9.service $TARGET/multi-user.target.wants/console-log-9.service

Did that, works fine. Thanks.

>But then again I really don't grok what you are trying to do, maybe I
>misread your intentions entirely.

No, you didn't. This was very helpful.

The documentation in systemd.generator(7) is a bit terse in that regard. 
I am not sure whether one can assume that a person reading this can 
makes sense from "the usual .wants/ and .requires/ symlinks". That part 
of systemd is usually abstracted away via the systemctl enable interface 
so people might use systemd daily and still not have the fact that this 
is controlled by symlinks in the filesystem on their radar. I'd add a 
few more words to that regard any maybe even an example.

Greetings
Marc


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