What is Run Levels in Linux

Run Levels:

The “run level” term is refer to a way of process in one of the operating system of computer that execute initialization in V- style of Unix System. Usually, seven run levels are present, numbered from 0 to 6.
“Run level” explains the status of the machine or appliance after boot. Different run levels are normally defined to:

• single-user mode
• multi-user mode with no any network services started
• multi-user mode having network services started
• system shutdown
• system reboot

 

Linux:
The Linux is an operating system that can be used of run levels by the application of sysvinit project. After the boot of Linux kernel, the init application reads the file the/etc/inittab to verify the action for every run level. If the user identifies other value as a parameter of kernel boot, the system will try to start the default run level.

Typical Linux run levels

Mostly distributions of Linux, further to the average run levels, explain the following further run levels:

Debian Linux:

0= Halt

1= single-User mode

2-5 =Full Multi-users with console logins and show manager if installed

6 =Reboot

Red Hat Linux and Fedora:

0= Halt

1= single-User mode

2=Multi-users style console logins only without networking.

3= Multi-User mode, console logins only

4=Not used/ User-definable

5= Multi-User mode, with display manager as well as console logins (X11)

6=Reboot

Slackware Linux:

0= Halt

1= single-User mode

2=not used to configured the similar as run level 3.

3=Multi-User with no show or display manager

4=Multi-User mode having display manager.

5= not used to configured the similar as run level 3.

6=Reboot

Arch Linux:

0= Halt

1= single-User maintenance mode

2=Not Used

3=Multi-User

4=Not Used

5=Multi-user with X11
6=Reboot

Gentoo Linux:

0= Halt

1= single-User mode

2=Multi-user mode with no networking

3=Multi-user mode

4=Aliased for run level 3

5=Aliased for run level 3

6=Reboot

UNIX:

System V Run levels

0= Shut down system, power-off if hardware leads it (only available from the console)

1= Single-User mode, all systems of file decreased but root, all methods except console procedures killed

2=Multi-user mode

3=Multi-User mode with  RFS (and  NFS in Release 4) file systems exported

4= Multi-User, User-definable

5= Halt the operating system, enter to firmware

6=Reboot

Solaris run levels:

0= Operating system stopped; SPARC  only) release to  Open Boot  timely

1= Single-User mode having all local file systems increases (read-write)

2= Multi-User mode having most daemons started

3= Multi-User mode; identical to 2 (run level 3 runs both /sbin/rc2 and /sbin/rc3), with file systems exported, plus some other network services in progress.

4= Another Multi-User mode, User-definable

5= Alternative Multi-User mode, User-definable

6=Reboot

Changing Run Levels of Linux:

If user is moving to high run levels, then user may create further services accessible to user, whereas taking step to lower run level will trigger daemons to become not accessible. On the creation of server, run level 3 is the usually utilized and hardly ever modified. Nevertheless, several tasks of administrative need the manager or administrator to run system toward run level 1 such as single user mode.

Init command is used to modify run levels:
#init1
Run level and process

To move toward run level 3, user needs to write init 3

Typing init 3 will move system to run level 3: