Operating System

Check OS version

ls /etc/*release*

cat /etc/*release*

We have some types of run levels

Traditional Runlevel	Description	systemd Target
Runlevel 0	Halt	poweroff.target
Runlevel 1	Rescue	rescue.target
Runlevel 2	Single-user	multi-user.target
Runlevel 3	Multi-user	multi-user.target
Runlevel 4	Custom	User-defined target
Runlevel 5	Graphical	graphical.target
Runlevel 6	Reboot	reboot.target

The main levels are 3, 5.

To see run levels

systemctl list-units | grep -i target

Check run level

runlevel

who -r

systemctl get-default

systemctl set-default multi-user.target