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OPS235 Lab 2 - Fedora17

231 bytes added, 23:39, 18 January 2010
Investigation 3: What is a runlevel?
===Investigation 3: What is a runlevel?===
Investigation 3:What After the kernel boots, it starts a single program, called <code>init</code>. A running instance of a program is called a '''process''' -- the init process always has a runlevel?process ID (PID) of 1. All other processes on the system are started by init, or they are started by processes started by init. Most current Linux systems use some variation of the init system originally developed for Unix System V (called "sysvinit") or a newer version called "upstart".    These program use a a configuration file named <code>/etc/inittab</code> (the filename suffix "tab" is short for "table"). 
All the system processes running on your system are controlled by the "init" process which has the process ID (pid) of 1. And this process is the "granddaddy" of all the other processes on your system.
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.
A great explanation of init and its place in the boot process can be found here.
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:

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