[systemd-devel] user service not starting on login

[Mantas Mikulėnas]

On Fri, May 10, 2019 at 5:22 AM Matt Zagrabelny <mzagrabe at d.umn.edu> wrote:

> Greetings,
>
> I am attempting to get a user service running on my session login.
>
> The unit is called jack. I've enabled it via:
>
> $ systemctl --user enable jack
>
> When I boot up the system and log in I see that it is inactive. I can
> start it manually without issue:
>
> $ systemctl --user status jack
> ● jack.service - JACK 2
>    Loaded: loaded (/home/theophilus/.config/systemd/user/jack.service;
> enabled; vendor preset: enabled)
>    Active: inactive (dead)
>
> $ journalctl --user -u jack -b
> -- Logs begin at Thu 2019-05-09 20:54:31 CDT, end at Thu 2019-05-09
> 21:13:53 CDT. --
> -- No entries --
>
> $ systemctl --user cat jack
> # /home/theophilus/.config/systemd/user/jack.service
> [Unit]
> Description=JACK 2
> Before=sound.target
> Before=pulseaudio.service
> Requires=dbus.socket
>
> [Service]
> Type=dbus
> BusName=org.jackaudio.Controller
>

Among other things, the bus name seems to be incorrect. In jack2-dbus the
only claimed name appears to be "org.jackaudio.service".


> ExecStart=/usr/bin/jack_control start
>

The jack_control program does not spawn nor directly execute the actual
jackd daemon. Instead it *remotely* activates org.jackaudio.service through
D-Bus (you'll see jackdbus under the dbus.service cgroup), then sends it a
single method call and exits.

In other words, jack_control is not a Type=dbus service, it's a oneshot
script that controls another Type=dbus service. You can imagine that it's
just a wrapper around `dbus-send` or `gdbus call`, and is something you'd
instead use in JACK's *ExecStartPost=*.

A direct conversion of jackdbus to a systemd service would look like this –
because of the way jackdbus is written, it always needs that extra command
to be sent over D-Bus (either by running `jack_control start` or by using
the manual tools):

(~/.config/systemd/user/jack.service)
[Service]
Type=dbus
BusName=org.jackaudio.service
ExecStart=/usr/bin/jackdbus auto
#ExecStartPost=/usr/bin/jack_control start
#ExecStartPost=/usr/bin/gdbus call -e -d org.jackaudio.service -o
/org/jackaudio/Controller -m org.jackaudio.JackControl.StartServer
ExecStartPost=/usr/bin/busctl call --user org.jackaudio.service
/org/jackaudio/Controller org.jackaudio.JackControl StartServer

I think you can even make manual jack_control invocations start your
systemd service using this:

(~/.local/share/dbus-1/services/org.jackaudio.service)
[D-BUS Service]
Name=org.jackaudio.service
Exec=/bin/false
SystemdService=jackservice

(Side note: The filename of the latter file should actually be
dbus-1/services/org.jackaudio.service.service [sic], but because JACK
already used the incorrect one in /usr/share, let's stick to it.)

-- 
Mantas Mikulėnas
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