Linux Runlevels

從 Initialization sequence in GNU/Linux 摘錄出來：

A runlevel describes the basic running state of the system

There are a number of runlevels that are, by convention, used to describe a working Linux system, with 2 or 3 being usual for a multi-user configuration. The complete list is given below (according the Linux Standards Base - LSB).

• Runlevel 0 (halt) - Shuts down everything and brings the system to halt.
• Runlevel 1 (single user) - Useful for maintenance work.
• Runlevel 2 (multi-user) - multi-user, but with no network services exported.
• Runlevel 3 (multi-user) - normal/full multi-user mode.
• Runlevel 4 (multi-user) - reserved for local use. Usually the same as 3.
• Runlevel 5 (multi-user) - multiuser, but boots up into X Window, using xdm, or similar.
• Runlevel 6 (Reboot) - As 0, but reboots after closing everything down.

Most systems default to 2, 3 or 5.