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:
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
