Red Hat Enterprise Linux Installation Guide 5.2 - linux.meuhobby.com

Chapter 30. Boot Process, Init, and Shutdown
S90xfs -> ../init.d/xfs
S95atd -> ../init.d/atd
S96readahead -> ../init.d/readahead
S97messagebus -> ../init.d/messagebus
S97rhnsd -> ../init.d/rhnsd
S99local -> ../rc.local
As illustrated in this listing, none of the scripts that actually start and stop the services are
located in the /etc/rc.d/rc5.d/ directory. Rather, all of the files in /etc/rc.d/rc5.d/ are
symbolic links pointing to scripts located in the /etc/rc.d/init.d/ directory. Symbolic links
are used in each of the rc directories so that the runlevels can be reconfigured by creating,
modifying, and deleting the symbolic links without affecting the actual scripts they reference.
The name of each symbolic link begins with either a K or an S. The K links are processes that
are killed on that runlevel, while those beginning with an S are started.
The init command first stops all of the K symbolic links in the directory by issuing the
/etc/rc.d/init.d/ stop command, where is the process to be killed. It
then starts all of the S symbolic links by issuing /etc/rc.d/init.d/ start.
Tip
After the system is finished booting, it is possible to log in as root and execute
these same scripts to start and stop services. For instance, the command
/etc/rc.d/init.d/httpd stop stops the Apache HTTP Server.
Each of the symbolic links are numbered to dictate start order. The order in which the services
are started or stopped can be altered by changing this number. The lower the number, the
earlier it is started. Symbolic links with the same number are started alphabetically.
Note
One of the last things the init program executes is the /etc/rc.d/rc.local
file. This file is useful for system customization. Refer to Section 3, “Running
Additional Programs at Boot Time” for more information about using the
rc.local file.
After the init command has progressed through the appropriate rc directory for the runlevel,
the /etc/inittab script forks an /sbin/mingetty process for each virtual console (login
prompt) allocated to the runlevel. Runlevels 2 through 5 have all six virtual consoles, while
runlevel 1 (single user mode) has one, and runlevels 0 and 6 have none. The /sbin/mingetty
process opens communication pathways to tty devices 2 , sets their modes, prints the login
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