SystemD

Service Files

SystemD service files have 3 sections:

  1. Unit: The information section - description and which services need to start before this one

  2. Service: Contains commands for env variables, execution and command to gracefully shutdown service

  3. Install: Which target requires this service (graphical target or multi-user target), can also define service alias

Note

You can use the man systemd.service and man systemd.unit commands to view some more info

Unit Section

  • Description: This is the description that gets printed when running the service, so make it sound cool!

  • After: You can specify the service runs after another service e.g.

After=network.target auditd.service

  • Documentation: Provides a link for user to view documentation on the service e.g. a https link

  • Before: Specify to run before another service

  • OnFailure: A space-seperated list of one or more units that are actived if this unit enters the β€œfailedβ€œ state

  • ConditionPathExists: Only starts if file in given path exists (use the ! to do the opposite)

Service Section

  • Type: simple,exec, forking, oneshot, dbus, notify, idle

  • ExecStart: Commands (with their arguments) that are executed when the service is started e.g.

ExecStart=/usr/bin/hellocmake --options

  • ExecStartPre/ExecStartPost: Commands to execute before/after ExecStart. Could be same program just with different arguments passed in

  • WatchdogSec: Configure a watchdog for the service, which fails if the service doesn’t call sd_notify(3) more frequently that the specified number of seconds

  • StandardOutput: Set where the standard output is sent. Set this to tty if you want the ouput on your terminal.

  • User: Create a user for this service, means that service is not run with root privileges

  • Environment: Specify environment variables for the service

  • EnvironmentFile: Specify location of file containing env variables

  • Restart: Lists situations where restart is triggered e.g. Restart=on-failure will restart if executable returns a non 0 value

Install Section

  • WantedBy: Specifies the target that will want this service - multi-user / graphical

  • Alias: another name for starting/stopping a service

SystemD Management

Some SystemD commands
systemctl enable name.service
systemctl disable name.service
systemctl status name.service
systemctl is-enabled name.service
systemctl list-unit-files --type service

Systemd services are classified by targets, formally known as runlevels in sysvinit. You can change these targets with systemctl. Examples of targets are multi-user and graphical. To view targets available, use:

Viewing SystemD targets
systemctl list-units --type target
systemctl list-units --type target --all

If you want to edit a service file, and see the changes instantly, use:

systemctl daemon-reload

Example adding a custom service

Here we give an example of how you would setup a service that runs a WSGI server

Example service file
# Location: /etc/systemd/system/start-wsgi-server.service

[Unit]
Description = Start WSGI server
After = network.target

[Service]
User = user
RemainAfterExit = yes
WorkingDirectory = /home/user/
ExecStart = /home/user/start-wsgi-server

[Install]
WantedBy = multi-user.target
Example service script
#!/bin/bash
# Location: $HOME/start-wsgi-server

set -euox pipefail

cd "$HOME/server"

source .venv/bin/activate

gunicorn -b 0.0.0.0:4000 flask_server:app --access-logfile flask_log.txt --daemon

You would also have to change some file permissions and enable the service:

Example setting up service
chmod 644 /etc/systemd/system/start-wsgi-server.service
systemctl enable start-wsgi-server.service