→Investigation 3: What is a runlevel?
===Investigation 3: What is a runlevel?===
The purpose of the "init" process is to start and stop other programs in a particular sequence according to the file called /etc/inittab and other files in various directories under the /etc/rc.d/init.d/ directory.
At any given time on a Linux/Unix system, a pre-defined set of base processes are running according to the so-called "runlevel" of the system which can be set by the init process. The init process gets the value for the system's runlevel from its main configuration file /etc/inittab. A system's runlevel can also be changed by using the init or telinit commands (they are equivalent in Linux). A system's runlevel is usually denoted with a number from 0 through 6; different systems may have a different set of base processes for each "runlevel", but these descriptions usually apply: