System Service Management (systemd) Flashcards

Which systemctl command displays the current state of a service, including its active state, PID, and recent log lines?

Answer: systemctl status sshd

`systemctl status sshd` shows the service's active state, PID, enabled status, and recent journal output in a human-readable format.

What file does systemd read to determine which target to boot into by default?

Answer: /etc/systemd/system/default.target

`/etc/systemd/system/default.target` is a symlink managed by `systemctl set-default` that determines the default boot target.

A service unit file contains `Type=forking`. What does this mean?

Answer: The parent process exits after forking a child, and the child becomes the main process

With `Type=forking`, systemd expects the parent process to exit after forking, and tracks the child (often via PIDFile=) as the main service process.

Which directive in a [Service] section tells systemd to restart a service whenever it exits, regardless of exit code?

Answer: Restart=always

`Restart=always` causes systemd to restart the service on any exit condition, including clean exits.

You want to see all units that have failed. Which command shows only failed units?

Answer: systemctl --failed

`systemctl --failed` lists all units currently in a failed state.

Which systemd target is the typical equivalent of SysV runlevel 3 (multi-user, no GUI)?

Answer: multi-user.target

`multi-user.target` corresponds to SysV runlevel 3, providing a fully operational multi-user environment without a graphical display manager.

What does the `WantedBy=multi-user.target` line in a unit's [Install] section do when you run `systemctl enable`?

Answer: It creates a symlink in multi-user.target.wants/ so the unit starts when that target is reached

`systemctl enable` creates a symlink under `/etc/systemd/system/multi-user.target.wants/` pointing to the unit file, causing it to be pulled in at boot.