[systemd-devel] Why is the [Install] section in a drop-in not respected?

[Zbigniew Jędrzejewski-Szmek]

On Tue, Oct 17, 2017 at 09:49:36AM +0000, 林自均 wrote:
> Hi folks,
> 
> I learned that [Install] section in a drop-in is not respected. This
> behavior is documented, but I failed to see *why*.
> 
> I found this related GitHub issue:
> https://github.com/systemd/systemd/issues/1774, and here is the quote from
> "poettering commented on 5 Nov 2015":

Hi,

things have changed a bit since then, and if somebody writes the code to honour
[Install] section in dropins, I expect it'd be merged.

Back then we didn't have support for drop-ins in /usr/lib, and
drop-ins were only expected to be used by users to _override_
configuration provided by packagers.  But now drop-ins in /usr/lib are
supported everywhere, and it's understood that packaging configuration might
be composed from a few independent pieces.

Zbyszek

> > Well, this has been requested before, but generally, install info is
> something that is provided by the unit file vendor in the unit files.
> drop-ins and symlinks in /etc are user extensions however. "systemctl
> enable" is for applying that install info to /etc. It would be
> contradictory to use user configuration to create user configuration
> though. Hence we do not respect install info in drop-ins.
> 
> However, I don't think it's contradictory since drop-ins are not always
> user configuration. For "s.service", the drop-ins in
> /usr/lib/systemd/system/s.service.d/
> and /var/run/systemd/generator/s.service.d/ are respected, but they are not
> user configurations.
> 
> For example, one can create a package that includes 2 things:
> 
> 1. a target unit called "remote-access.target"
> 2. a systemd generator that generates the following drop-ins for
> "sshd.service", "telnetd.service" and "vnc.service":
> 
> [Unit]
> PartOf=remote-access.target
> 
> [Install]
> WantedBy=remote-access.target
> 
> That way, after a user typed "systemctl enable sshd telnetd vnc", he/she
> can:
> 
> - systemctl start remote-access.target
> - systemctl stop remote-access.target
> 
> to conveniently start/stop all remote access services.
> 
> In conclusion, I consider drop-ins as a way to enhance the original unit
> files. Just like [Unit], [Service] or any other sections, [Install] should
> be enhance-able too.