init

Set system to graphical environment (runlevel 5)

$ sudo init 5

$ sudo init 3

$ sudo init 1

$ init 0

$ init 6

init [runlevel]

init is the parent of all processes on the system, responsible for starting and stopping services at different runlevels. It is the traditional System V init daemon that manages the system state.
Runlevels define different system states, from single-user maintenance mode to full graphical desktop. Changing runlevels causes init to start or stop services as defined in /etc/rc.d or /etc/init.d scripts.
On modern systemd-based systems, init may be a compatibility wrapper that translates runlevel commands to systemd targets.

0

Halt the system

Single user mode (maintenance)

Multi-user mode without networking (Debian) or with networking (Red Hat)

Multi-user mode with networking and text console

Multi-user mode with networking and graphical desktop

Reboot the system

Behavior varies between distributions. On systemd systems, requires SYSVINIT compatibility. Direct runlevel changes can disrupt running services.

System V init originated in AT&T UNIX System V in 1983. It was the standard init system on most Linux distributions until systemd began replacing it around 2011.

systemctl(1), runlevel(8), telinit(8)