Linux utilizes what is called "runlevels". A runlevel is a software configuration of the system that allows only a selected group of processes to exist. Init can run the system in one of eight runlevels. These runlevels are 0-6 and S or s. The system runs in only one of these runlevels at a time. Typically these runlevels are used for different purposes. Runlevels 0, 1, and 6 are reserved. For Redhat Linux version 6, the runlevels are:
0 | - | halt | ||
1 | - | Single user mode | ||
2 | - | Multiuser, without NFS (The same as 3, if you don't have networking) | ||
3 | - | Full multiuser mode | ||
4 | - | unused | ||
5 | - | X11 | ||
6 | - | Reboot |
1. level 0 : to halt the system, it reboots the systems again and again after login in
2. level1 :single user mode, this is a special mode in which only one use ie the super user mode in which limited system based linux commands work.
3. level2-level5 : this is the multi user mode in which the system works at its full potential with all the command set that it supports
4. level 6 : entering into this level reboots the system.
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