Understanding CentOS 6 Runlevels

About Runlevels:

A runlevel is one of the modes that a Unix -based operating system will run in.                 A runlevel defines the state of the machine after boot. During the boot sequence, a process named init looks in the /etc/inittab file to find the default runlevel.

CentOS 6 Runlevels Descriptions

The following runlevels are defined by default under Red Hat Enterprise Linux:

• Runlevel 0 – The halt runlevel. This is used for Shut down the system.

• Runlevel 1 – This runlevel Start up in a single user mode under which only the root user can log in. This run level is only for system administrators to perform system maintenance or repair activities.

• Runlevel 2 – This runlevel is used for Boots the system into a multi-user mode with text based console login capability. This runlevel does not start the network.

• Runlevel 3 – This runlevel is used for Full Multi-user mode with Graphical desktop environment. Similar to runlevel 2 except that networking services are started.

• Runlevel 4 – Undefined runlevel. This runlevel can be configured to provide a custom boot state.

• Runlevel 5 –  This runlevel Boots the system into a networked, multi-user state with X Window System capability. By default the graphical desktop environment will start at the end of the boot process.

• Runlevel 6 – This runlevel is Reboots the system.

Find out our default run level using the following command.

& you can also use this command to check out the default runlevel

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Changing the Default runlevel:

The default runlevel for an CentOS 6 system is defined within the /etc/inittab file, use your preferred editor to edit the file

Find out the above line and edit your default runlevel, the current runlevel is 3, if you need to change the default runlevel 5 means you will edit the file like the below

id:5:initdefault:

save and exit using the :wq command

Finally reboot the system then see the changes in the runlevel.

Thank you……!