Runlevels

• different system states. runlevels are labeled by numbers ranging from 0 to 6 which present different run states.

• Runlevel 0 – halted system state, the system shuts down all running processes and unmounts all file systems then shuts down

• Runlevel 1 – single user mode, a state where only a single user can log in to the system. only a few processes are started in single-user mode, so its useful to diagnose what is causing the system to not start.

• Runlevels 2 through 5 – left up to the distro and you to define. red hat has a graphical option set to 5 and a system with no graphics set to 3.

• Runlevel 6 – reserved for rebooting the server.