Units

Question 1

What is systemd and its purpose?

Answer 1

systemd manages system startup and service behavior.

Question 2

What do unit files define?

Answer 2

Configuration for specific system components.

Question 3

Name common systemd unit types.

Answer 3

Services; Targets; Mounts; Timers.

Question 4

What do service units manage?

Answer 4

Background programs and daemons.

Question 5

What is the file extension for service units?

Answer 5

.service.

Question 6

What are the sections in a service unit file?

Answer 6

[Unit], [Service], [Install].

Question 7

What does Description= in [Unit] do?

Answer 7

Provides summary.

Question 8

What do Requires= and Wants= in [Unit] define?

Answer 8

Dependencies.

Question 9

What do Before= and After= in [Unit] define?

Answer 9

Startup order.

Question 10

What does Type= in [Service] define?

Answer 10

Process behavior; simple for foreground scripts; forking for daemons.

Question 11

What does ExecStart= specify?

Answer 11

Start command.

Question 12

What does ExecStop= specify?

Answer 12

Stop method.

Question 13

What does User= specify?

Answer 13

Non-root execution account.

Question 14

What does WantedBy= in [Install] define?

Answer 14

Startup target; used with systemctl enable.

Question 15

Give common systemctl commands for services.

Answer 15

sudo systemctl start app; sudo systemctl enable app; sudo systemctl status app.

Question 16

What do targets define?

Answer 16

System states by grouping services.

Question 17

Name common targets.

Answer 17

multi-user.target (non-graphical with networking); graphical.target (GUI mode); network-online.target (full network connectivity).

Question 18

How to view current default target?

Answer 18

systemctl get-default.

Question 19

How to set a new default target?

Answer 19

systemctl set-default graphical.target.

Question 20

What do mount units manage?

Answer 20

File system mounts using .mount files; preferred over /etc/fstab.

Question 21

What sections do mount units include?

Answer 21

[Unit], [Mount], [Install].

Question 22

List common mount directives.

Answer 22

Description; After=local-fs.target; What=source; Where=mount location; Type=file system type; Options=behavior; WantedBy=multi-user.target.

Question 23

How to enable and start a mount?

Answer 23

sudo systemctl enable mnt-usbdrive.mount; sudo systemctl start mnt-usbdrive.mount.

Question 24

What do timer units do?

Answer 24

Schedule tasks; replace or supplement cron jobs; paired with .service files.

Question 25

Name common timer directives.

Answer 25

OnBootSec=delay after boot; OnCalendar=calendar syntax; Persistent=true for missed runs.

Question 26

Give an example of a timer configuration.

Answer 26

backup.timer: Type=oneshot; OnCalendar=*-*-* 02:00:00; Persistent=true; enable with systemctl enable.