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commands to configure the system's serial ports. Refer to the
setserial
for more information.
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
directory, are the
,
rc
rc.local
the following 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 runlevels configured by default
under Red Hat Enterprise Linux.
4.1. Runlevels
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 determine 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,
can quickly change the mode of the machine without the user manually stopping and starting
services.
The following runlevels are defined by default under 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
,
, and, optionally, the
rc.sysinit
SysV Init Runlevels
setserial
directory. Within this
/etc/rc.d/
rc.serial
command when controlling
/sbin/init
man page
init
scripts as well as
.
init
init
9
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