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====== Automation: cron, systemd timers, watchers ======

===== cron: quick and familiar =====

<code bash>
crontab -e        # user crontab (no sudo needed)
</code>

<code bash>
# min hour dom mon dow  command
0 9 * * *        ~/bin/backup.sh >> ~/logs/backup.log 2>&1
@daily           ~/bin/daily.sh
@reboot          ~/bin/startup.sh
*/15 * * * *     ~/bin/frequent.sh
</code>

Gotchas: cron env is minimal: use absolute paths, set ''PATH'' in the crontab
(''PATH=/usr/local/bin:/usr/bin:/bin''), and ''SHELL=/bin/bash'' if needed. GUI
stuff won't work (no DISPLAY).

===== systemd timers: better logging, dependencies =====

Two files per timer, e.g. ''~/.config/systemd/user/backup.timer'' + ''.service'':

<code ini>
# backup.service
[Service]
Type=oneshot
ExecStart=%h/bin/backup.sh

# backup.timer
[Unit]
Description=Daily backup

[Timer]
OnCalendar=daily
Persistent=true          # catch up if the machine was off

[Install]
WantedBy=timers.target
</code>

<code bash>
systemctl --user daemon-reload
systemctl --user enable --now backup.timer
systemctl --user list-timers        # next run times
journalctl --user -u backup.service # logs
</code>

System-wide equivalents are stored in ''/etc/systemd/system/'' and run as root
(''systemctl'' without ''--user''). The macbook-qol PROCHOT service is an example
of a oneshot system unit.

''OnCalendar'' cheat sheet: ''daily'', ''hourly'', ''weekly'',
''Mon..Fri 09:00'', ''*:0/15'' (every 15 min), ''boot'' (''OnBootSec=5min'').

===== LXQt autostart (GUI apps) =====

''lxqt-config-session'' → Autostart → Add. Or drop a file in
''~/.config/autostart/thing.desktop'':

<code ini>
[Desktop Entry]
Type=Application
Name=Conky
Exec=conky -d
</code>

===== Watch a directory: inotifywait =====

<code bash>
sudo apt install inotify-tools
inotifywait -m -e modify,create ~/watchdir | while read -r _ _ f; do
  echo "changed: $f"; ./rebuild.sh
done
</code>

Systemd path units also exist (''*.path'' with ''PathModified=''), good for
"run this when a file appears".

===== One-off delayed jobs: `at` =====

<code bash>
sudo apt install at
echo 'notify-send "tea"' | at now + 5 minutes
echo './job.sh' | at 03:00 tomorrow
atq && atrm <job#>
</code>

===== Long-running personal daemons =====

User service without root (''~/.config/systemd/user/thing.service''):

<code ini>
[Service]
ExecStart=%h/bin/thing --serve
Restart=on-failure

[Install]
WantedBy=default.target
</code>

''systemctl --user enable --now thing''. For it to run //without// login:
''loginctl enable-linger $USER''.

===== See Also =====

* [[terminal:scripting:start|Scripting Index]]
  * [[terminal:tools:start|CLI Tools]]
  * [[terminal:start|Return to terminal]]
  * [[start|Return to wiki home]]

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