Run Level
Most versions of Unix use different run levels to define different operational and states of the Unix system. The "init" command is used to change the run level. Other commands which change the run level include reboot, halt, and shutdown. RedHat Linux Run Levels: Run Level Description 0 Halt 1 Single user mode 2 Multiuser mode without NFS 3 Full Multiuser mode 4 Unused 5 X11 ..