Run levels in Linux

The following runlevels are defined by default under Red Hat Enterprise Linux:

• 0 — Halt
• 1 — Single-user text mode
• 2 — Not used (user-definable)
• 3 — Full multi-user text mode
• 4 — Not used (user-definable)
• 5 — Full multi-user graphical mode (with an X-based login screen)
• 6 — Reboot

How to define default run level:

Edit the /etc/inittab:

id:5:initdefault:

Runlevel Utilities

One of the best ways to configure runlevels is to use an initscript utility. These tools are designed to simplify the task of maintaining files in the SysV init directory hierarchy and relieves system administrators from having to directly manipulate the numerous symbolic links in the subdirectories of /etc/rc.d/.

Red Hat Enterprise Linux provides three such utilities:

• /sbin/chkconfig — The /sbin/chkconfig utility is a simple command line tool for maintaining the /etc/rc.d/init.d/ directory hierarchy.
• /usr/sbin/ntsysv — The ncurses-based /sbin/ntsysv utility provides an interactive text-based interface, which some find easier to use than chkconfig.
• Services Configuration Tool — The graphical Services Configuration Tool (system-config-services) program is a flexible utility for configuring runlevels.