Sysv Init Runlevels - Red Hat ENTERPRISE LINUX 3 Reference Manual

Chapter 1. Boot Process, Init, and Shutdown
The
/etc/rc.serial
commands to configure the system's serial ports. Refer to the
setserial
for more information.

1.4. SysV Init Runlevels

The SysV init runlevel system provides a standard process for controlling which programs
launches or halts when initializing a runlevel. SysV init was chosen because it is easier to use and
more flexible than the traditional BSD-style init process.
The configuration files for SysV init are located in the
are the ,
rc rc.local
directories:
init.d/
rc0.d/
rc1.d/
rc2.d/
rc3.d/
rc4.d/
rc5.d/
rc6.d/
The directory contains the scripts used by the
init.d/
services. Each of the numbered directories represent the six default runlevels configured by default
under Red Hat Enterprise Linux.
1.4.1. Runlevels
Runlevels are a state, or mode, defined by the services listed in the SysV
directory, where
x
The idea behind SysV init runlevels revolves around the idea that different systems can be used in
different ways. For example, a server runs more efficiently without the drag on system resources
created by the X Window System. Or there may be times when a system administrator may need
to operate the system at a lower runlevel to perform diagnostic tasks, like fixing disk corruption in
runlevel 1.
The characteristics of a given runlevel determines which services are halted and started by
For instance, runlevel 1 (single user mode) halts any network services, while runlevel 3 starts these
services. By assigning specific services to be halted or started on a given runlevel,
change the mode of the machine without the user manually stopping and starting services.
The following runlevels are defined by default for Red Hat Enterprise Linux:
— Halt
• 0
— Single-user text mode
• 1
— Not used (user-definable)
• 2
— Full multi-user text mode
• 3
— Not used (user-definable)
• 4
— Full multi-user graphical mode (with an X-based login screen)
• 5
— Reboot
• 6
script is used if serial ports must be setup at boot time. This script runs
, , and, optionally, the
rc.sysinit
is the number of the runlevel.
directory. Within this directory,
/etc/rc.d/
scripts as well as the following
rc.serial
command when controlling
/sbin/init
/etc/rc.d/rc x .d/
man page
setserial
init
init
can quickly
init
7
.