systemd.md

systemd

daemon reload
after changed

systemctl daemon-reload

start / stop / restart / reload

systemctl start <unit ...>
systemctl stop <unit ...>
systemctl restart <unit ...>
systemctl reload <unit ...>
systemctl reload-or-restart <unit ...>

enable / disable

systemctl enable <unit ...>
systemctl disable <unit ...>

view

systemctl cat <unit>

alias

ln -s /lib/systemd/system/{<unit>,<alias>}.service

override some value

• drop-in file (partial with section header) /etc/systemd/system/<unit>.service.d/override.conf
  • or systemctl edit <unit> - reload automatically on save (version 218+)
• override file (whole file) cp /lib/systemd/system/<unit>.service /etc/systemd/system
  • or systemctl edit --full <unit> - reload automatically on save (version 218+)

service file

! comments not allowed in the same line !

[Unit] - depends and orders
<unit>.service

[Unit]
Description=...
Requires=<unit2>.service   # depend - need
# Wants=<unit2>.service    # depend - optional
Before=<unit2>.service     # order - start before
After=<unit0>.service      # order - start after (succeeded or failed)
BindsTo=<unit>.service     # depend - stop if unit2.service stopped

[Service] - environment and commands sequence
<unit>.service
ExecStart=... on system startup
ExecStop=... on system shutdown / reboot

[Service]
...
Environment=<VAR=value>
ExecStartPre=<command1>
ExecStartPre=<command2>
ExecStart=<command>      # allow only 1 command except Type=oneshot
ExecStartPost=<command3>
ExecStartPost=<command4>
...

[Install] - link to target directories

[Install]
WantedBy=<target>

---

list all units

systemctl list-unit-files

list units by filter

systemctl | grep <unit1\|unit2>

list by state enabled / disabled / indirect / static

systemctl list-unit-files | grep <state>

Before shutdown

[Unit]
Description=Before shutdown
DefaultDependencies=no  # not wait for anything
Requires=network.target # before network stop
Before=reboot.target poweroff.target halt.target

[Service]
Type=oneshot            # wait until this service finished
RemainAfterExit=true    # for no real ExecStart
ExecStart=/bin/true     # for no real ExecStart
ExecStop=<script>       # run on system shutdown / reboot

[Install]
WantedBy=multi-user.target # run at multi-user on system start