Bug#886812: service: start/stop tries to use invalid systemd units when using socket templates

[Cyrill Troxler]

On Wed, 2018-01-10 at 12:23 +0100, Michael Biebl wrote:
> Am 10.01.2018 um 09:57 schrieb Cyrill Troxler:
> > Package: init-system-helpers
> > Version: 1.48
> > 
> > I stumbled upon a issue with the start/stop triggers when using
> > systemd
> >  socket templates on Debian stretch. I started getting unrelated
> > error
> > messages when entering `service some_service start` on a system
> > which
> > has a systemd socket template defined. The issue is quite easy to
> > replicate:
> > 
> > ```
> > # touch /etc/systemd/system/test at .socket
> > # service cron start
> > Failed to get properties: Unit name test at .socket is not valid.
> > ```
> > 
> > I have tracked down the issue to line 205 in /usr/sbin/service.
> > (line
> > 182 in 1.51)
> > ```
> > for unit in $(systemctl list-unit-files --full --type=socket
> > 2>/dev/null | sed -ne 's/\.socket\s*[a-z]*\s*$/.socket/p'); do
> >     if [ "$(systemctl -p Triggers show $unit)"
> > 
> > ```
> > Here it gets all unit files and then tries to show get the Triggers
> > of
> > that unit. This not only causes the error message shown above, it
> > also
> > causes not stopping the actual socket units like it is described in
> > the
> > comment above line 205. The issue could be solved by using `list-
> > units` 
> > instead of `list-unit-files` because `list-units` will only list
> > actual
> > socket units and not their templates.
> 
> Afaics the problem is that you created an invalid (empty) .socket
> template file.
> The problem with list-units afair was, that it only shows units which
> are currently in memory.
> 
> 

I stumbled onto this with a valid .socket template. The issue is that
`systemctl -p Triggers show $unit` happens with the name of the
template because `list-unit-files` does not show any of the instances
spawned by templates. For reference, here's a valid template that I've
tried:

```
# /etc/systemd/system/test at .socket
[Unit]
Description=Test Socket %i

[Socket]
ListenStream=127.0.0.1:1234

[Install]
WantedBy=sockets.target
```

If `list-units` only shows units which are in memory, is that not what
we want anyway? Or is it possible to start/stop units which are not in
memory? With `list-units` and `--all` it would also show inactive ones.

Cyrill