[systemd-devel] Services with Access to User Sessions

[Justin Brown]

Mantas,

Thanks for the reply. I was able to convert the system service to a
user service. Shairport is able to connect to PulseAudio just fine
now. It's having trouble connecting to Avahi, which I'll need to
figure out, but at least I'm making progress.

Cheers,
Justin

On Mon, May 19, 2014 at 2:14 PM, Mantas Mikulėnas <grawity at gmail.com> wrote:
> On Mon, May 19, 2014 at 9:55 PM, Justin Brown <justin.brown at fandingo.org> wrote:
>>
>> I'm having some difficulty setting up a systemd service that needs
>> access to a "user session" (probably not the correct term). I want to
>> configure shairport as a systemd service. Shairport is an open source
>> implementation of Apple's AirPlay and is used to play audio from an
>> iOS device on a Linux computer. As such, it needs access to
>> PulseAudio. This is where I'm having trouble.
>>
>> I have a basic shairport.service file setup, and it correctly starts,
>> but it does not seem to connect to PulseAudio because there is no
>> audio output, even though the iOS device shows that audio is being
>> transmitted.
>>
>> [Unit]
>> Description=Shairport AirTunes receiver
>> After=sound.target
>> Requires=avahi-daemon.service
>> After=avahi-daemon.service
>>
>> [Service]
>> ExecStart=/usr/local/bin/shairport -v
>> Restart=always
>>
>> [Install]
>> WantedBy=multi-user.target
>>
>> I need some help addressing two points.
>>
>> 1) What do I need to change to allow this service to connect to
>> PulseAudio in my desktop session?
>> 2) Following on #1, how can I start this application only once a user
>> logs in (i.e. PulseAudio can play audio)?
>
> To both questions – it cannot easily be done from a system service, as
> there can be zero or multiple desktop sessions at any moment. On the
> other hand, if your systemd version is recent enough (v205+, I
> think?), then you can run this as a _user_ service. [1]
>
> When a user logs in, logind starts an instance of user@<uid>.service
> for them, which starts "default.target" according to what's in
> {~/.config,/etc,/usr/lib}/systemd/user/. It is not _completely_
> connected to the desktop session right now – e.g. it won't know the
> right $DISPLAY or $XAUTHORITY unless the X11 startup scripts call
> `systemctl --user {set,import}-environment`. However, it should work
> just fine for PulseAudio, which uses static paths for its socket &
> cookie. I have been running mpd & pulseaudio as user services for the
> past few months without any problems.
>
> One minor downside is that right now a user service cannot depend on,
> or be ordered against, a system service – so
> "After=avahi-daemon.service" will be a no-op and
> "Requires=avahi-daemon.service" will never succeed. (Though I think
> one could work around this with a fake .service and a short perl
> script that just watches bus names...)
>
> You can use `systemctl --user` to control your user services.
>
> [1] It's possible to use user at .service in some older systemd versions
> as well, but it's not auto-started until v205, and there are other
> small differences.
>
> --
> Mantas Mikulėnas <grawity at gmail.com>