Runlevels
The term runlevel refers to a mode of OS initialization in Unix or similar operating systems. Runlevels are sort of like profiles that your computer uses to determine which services to launch in the background when you boot. The most commonly used runlevels are Runlevel 5 and Runlevel 3.
Runlevels may vary from one OS to another. The runlevels in Red Hat Linux are –
0 | Halt | Shuts down the machine. |
1 | Single-User Mode | Typically used for recovery. Does not configure network interfaces, start daemons, or allow non-root logins. |
2 | Multi-User Mode | Does not configure network interfaces or start daemons. |
3 | Multi-User Mode with Networking | Starts the system normally and provides the BASH shell. |
4 | Not used/User-definable | For special purposes |
5 | X11 | Full graphical mode managed by X-Server. |
6 | Reboot | Reboots the computer. |
Setting the Runlevel
The runlevel that the system would log into by default is defined in /etc/inittab
#### /etc/inittab ####
init:5:initdefault
This line indicates that the system would log into runlevel 5 by default. Changing the value to something else would also change the default runlevel.
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