systemd

An init system on Linux, used on Ubuntu and other distros.

Cheatsheet

• systemd on the Arch Linux wiki
• systemd by example

Commands

# reload config files
sudo systemctl daemon-reload

# the full name is 'foo.service'
# '.service' is assumed if not specified
sudo systemctl start foo
sudo systemctl stop foo
sudo systemctl restart foo
sudo systemctl status foo

# view config
sudo systemctl cat foo

# view logs
sudo journalctl -u foo

Non-root services

Set-up (courtesy of Stack Overflow):

1. Add your user to the group: sudo usermod -a -G systemd-journal $USER
2. Log back in.
3. mkdir -p ~/.config/systemd/user
4. Put your service files in that directory. Remove any User or Group directives.
5. Set up lingering so services can run without logging in: loginctl enable-linger $USER
6. systemctl --user daemon-reexec

Then:

systemctl --user daemon-reload
systemctl --user start foo
journalctl --user-unit foo

Service file

• Man pages at man 5 systemd.unit and man 5 systemd.service
• Unit section options
• Service section options
• More options

[Unit]
Description=Grafana

[Service]
ExecStart=/usr/bin/grafana server
User=ian
WorkingDirectory=/home/ubuntu/grafana
Environment="MY_VAR=value"
Environment="MY_VAR2=value"
Restart=always
# if restarts more than 3 times in 60 seconds, don't try to restart
# NOTE: before systemd v230, called `StartLimitInterval`
StartLimitIntervalSec=60s
StartLimitBurst=3
# wait 5 seconds in between restarts
RestartSec=5s

[Install]
# start service on system start-up
WantedBy=default.target

After versus Requires

• After establishes order: if service B has After=A, and service A and B are both being started up (e.g., because they both have WantedBy=default.target), then service A will be started before service B.
• Requires establishes dependency: if service B has Requires=A, and service B is being started up, then service A will also be started up (not necessarily before service B, unless After is also specified).
• Wants is like Requires but creates a weak dependency; systemd will try to start the other service but will still run the first service even if the other fails.

Bibliography

• "systemd, 10 years later: a historical and technical retrospective" (V.R., 2020)
• "The Tragedy of systemd" (Benno Rice @ YouTube, 2016)

See also

• notes/bad-ux