systemd

Table of Contents

1. Units

User units are stored in ~/.config/systemd/user/ and once activated they start when the user login so the network connection should be ready

1.1. Conditions

~$ systemd-analyze condition 'ConditionPathExists=%h/documents'
test.service: ConditionPathExists=/home/alan/documents succeeded.
Conditions succeeded.
~$ systemd-analyze condition 'ConditionHost=!foo'
test.service: ConditionHost=!foo succeeded.
Conditions succeeded.

1.2. Service units

1.2.1. Example

Starting SSH tunneling after the network stack has been started

Services using the network should hence simply place an After=network.target stanza in their unit files, without Wants=network.target or Requires=network.target. 

[Unit]
Description=Start the SSH tunnel
After=network.target
ConditionPathExists=%h/.ssh/config

[Service]
Type=simple
ExecStart=/usr/bin/ssh tunnel
Restart=always
RestartSec=120

[Install]
WantedBy=default.target

1.3. Timer units

A timer unit foo.timer is used for timer-based activation of a matching service unit foo.service

1.3.1. List user timers

systemctl --user list-timers --all

1.3.2. Example

  1. Timer unit

    Only the timer unit requires the [Install] section in this case 

    [Unit]
Description=Backup fish history every sunday at 01:00

[Timer]
OnCalendar=Sun 01:00
RandomizedDelaySec=5minutes
Persistent=true
Unit=backup-fish-history.service

[Install]
WantedBy=timers.target
  2. Service unit

    The %LETTER are specifiers, e.g. %h expand to /home/alan 

    [Unit]
Description=Backup fish history
After=network.target

[Service]
ExecStart=/usr/bin/rsync -avh %h/.local/share/fish/fish_history framboise:backup/%H/
  3. Enable the timer unit
    systemctl --user enable --now backup-fish-history.timer

    Check the logs with journalctl

1.3.3. Path units

[Unit]
Description=Monitor foo.txt for changes

[Path]
PathChanged=%h/foo.txt
Unit=foo.service

2. Scheduling

Use OnCalendar= directive for scheduling based on wall-clock time, as monotonic clock starts at boot time (e.g. using OnUnitActiveSec=1hour instead of OnCalendar=hourly)

To test the validity of the scheduled time 

systemd-analyze calendar "Sun 01:00" --iteration=5

Will output 

  Original form: Sun 01:00
Normalized form: Sun *-*-* 01:00:00
    Next elapse: Sun 2023-12-24 01:00:00 GMT
       From now: 5 days left
       Iter. #2: Sun 2023-12-31 01:00:00 GMT
       From now: 1 week 5 days left
       Iter. #3: Sun 2024-01-07 01:00:00 GMT
       From now: 2 weeks 5 days left
       Iter. #4: Sun 2024-01-14 01:00:00 GMT
       From now: 3 weeks 5 days left
       Iter. #5: Sun 2024-01-21 01:00:00 GMT
       From now: 1 month 3 days left

3. Command to run after any changes to unit files

systemctl --user daemon-reload

4. systemd-tmpfiles

Creates, deletes, and cleans up volatile and temporary files and directories

See tmpfiles.d.html

5. Symlinks poweroff, shutdown and reboot to systemctl

The systemctl command knows when it has been invoked via symlink (argument $0 returns the executed command name) 

~$ ls -l /usr/sbin/poweroff
lrwxrwxrwx 1 root root 14  6 mars  15:56 /usr/sbin/poweroff -> /bin/systemctl
~$ cat foo
#!/bin/sh
echo "Invoked by $0"
~$ ln -sv foo bar
'bar' -> 'foo'
~$ ./foo
Invoked by ./foo
~$ ./bar
Invoked by ./bar

6. Manpages

7. Related nodes

8. References