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Linux & Systems

systemd Essentials

intermediate

Understand units, write your own service, and control and debug it with systemctl and journalctl.

2 chapters25 min readlinuxsystemdservicesinit

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Chapters

  1. 1Units and unit files1 min read · 2 exercises
  2. 2systemctl and journalctl1 min read

Everything to remember

Every chapter's recap, in one place.

Units and unit files

Recap

  • systemd is PID 1 and manages every service as a unit.

  • Unit type is determined by the file suffix: .service, .socket, .timer, .target.

  • Local overrides belong in /etc/systemd/system, never in /usr/lib.

  • [Unit] sets ordering, [Service] sets how to run, [Install] sets what enables it.

systemctl and journalctl

Recap

  • daemon-reload after every unit file change, or systemd keeps the stale copy.

  • enable sets boot behaviour; start affects only the running system.

  • journalctl -u <unit> -f is the equivalent of tail -f on a service log.

  • systemctl edit creates a drop-in override and leaves the packaged unit intact.

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