Linux execution/boot levels

This is the first process that is run by the Linux kernel and is what loads the rest of the system.

There are a number of different execution/boot levels i.e. the mode the computer operates.

The default init is set by a variable called initdefault found in /etc/inittab.

The execution levels are;

0: Halt (i.e. shut down)
1: Single user - reduced set of services, used if others do not boot
2: All services excluding network
3: Full user (no GUI)
4: Not used
5: Full user (with GUI)
6: Reboot

To change the init level enter init [mode] (e.g. init 3). To change the init on startup, change the initdefault value in the inittab file.

To check which level you are on use the who -r command.

For more commands use man init.