2.4.2 Runlevels

After completing the boot process, init starts all services that are configured to run in the default runlevel. The default runlevel is given by the entry for id in /etc/inittab. Debian ships with id=2.

Debian uses the following runlevels:

• 1 (single-user mode),

• 2 through 5 (multiuser modes), and

• 0 (halt the system),

• 6 (reboot the system).

Runlevels 7, 8, and 9 can also be used but their rc directories are not populated when packages are installed.

Switch runlevels using the telinit command.

When entering a runlevel all scripts in /etc/rcrunlevel.d/ are executed. The first letter in the name of the script determines the way in which the script is run: scripts whose names begin with K are run with the argument stop. Scripts beginning with S are run with the argument start. The scripts are run in the alphabetical order of their names; thus "stop" scripts are run before "start" scripts and the two-digit numbers following the K or S determine the order in which the scripts are run.

The scripts in /etc/rcrunlevel.d are in fact just symbolic links back to scripts in /etc/init.d/. These scripts also accept "restart" and "force-reload" as argument; the latter methods can be used after a system has been booted in order to restart services or force them to reload their configuration files.

For example:

     # /etc/init.d/exim4 force-reload