JACK Projects as System Services

Henrik von Coler

In some applications, like headless or embedded systems, it can be helpful to autostart the jack server, followed by additional programs for sound processing. In this way, a system can boot into the desired configuration without additional user interaction. There are several ways of achieving this. The following example uses systemd services for a user named student.

The JACK Service

The JACK service needs to be started before the clients. It is a system service and needs just a few entries. This is a minimal example - depending on the application and hardware settings, the arguments after ExecStart=/usr/bin/jackd need to be adjusted.

[Unit]
Description=Jack audio server

[Install]
WantedBy=multi-user.target

[Service]
Type=simple
PrivateTmp=true
Environment="JACK_NO_AUDIO_RESERVATION=1"
ExecStart=/usr/bin/jackd -d alsa
User=student

The above content needs to be placed in the following file (root privileges are required for doing that):

/etc/systemd/system/jack.service

Afterwards, the service can be started and stopped via the command line:

$ sudo systemctl start jack.service
$ sudo systemctl stop jack.service

In order to start the service on every boot, it needs to be enabled:

$ sudo systemctl enable jack.service

If desired, the service can also be deactivated:

$ sudo systemctl disable jack.service

The Client Service(s)

Once the JACK service is enabled, client software can be started. A second service is created, which is executed after the JACK service. This is ensured by the additional entries in the [Unit] section. The example service launches a Puredata patch without GUI:

[Unit]
Description=Synthesis Software
After=jack.service
Requires=jack.service

[Install]
WantedBy=multi-user.target

[Service]
Type=idle
PrivateTmp=true
ExecStartPre=/bin/sleep 1
ExecStart=/usr/bin/puredata -nogui -jack ~/PD/test.pd
User=student

The above content needs to be placed in the following file:

/etc/systemd/system/synth.service

The service can now be controlled with the above introduced systemctl commands. When enabled, it starts on every boot after the JACK server has been started:

$ sudo systemctl enable synth.service