Chapter 3. Boot Process, Init, and Shutdown

61

The

init.d

directory contains the scripts used by the

init

command when controlling services.

Each of the numbered directories represent the six default runlevels configured by default under Red

Hat Linux. For more information on runlevels, see Section 3.6.

The default runlevel is listed in

/etc/inittab

. To find out the default runlevel for your system, look

for the line similar to the one below near the top of

/etc/inittab

:

id:3:initdefault:

The default runlevel listed in the example above is three, as the number after the first colon indicates.

If you want to change it, edit

/etc/inittab

as root.

Warning

Be very careful when editing /etc/inittab. Simple typos can cause your system to become un 

bootable. If this happens, you will either need a boot diskette for your system or you will need to enter

rescue mode to boot your computer and fix the file.

For more information on rescue mode, see the chapter titled Rescue Mode in the Official Red Hat

Linux Customization Guide.

3.6. Init Runlevels

The idea behind operating different services at different runlevels revolves around the fact that dif 

ferent systems can be used in a different ways. Some services cannot be used until the system is in a

particular state, or mode, such as ready for more than one user or has networking available.

There are times in which you may want to operate the system at a lower mode, such as fixing disk

corruption problems in runlevel 1, when no other users can possibly be on the system or leaving a

server in runlevel 3 without an X session running. In these cases, running services that depend upon

a higher system mode to function does not make sense because they will not work correctly anyway.

By already having each service assigned to start when its particular runlevel is reached, you ensure

an orderly start up process and can quickly change the mode of the machine without worrying about

which services to manually start or stop.

Generally, Red Hat Linux operates in runlevel 3 or runlevel 5   both full multi user modes. The

following runlevels are defined in Red Hat Linux:

  0   Halt

  1   Single user mode

  2   Not used (user definable)

  3   Full multi user mode

  4   Not used (user definable)

  5   Full multi user mode (with an X based login screen)

  6   Reboot

The default runlevel for a system to boot into and stop is configured in

/etc/inittab

. For more

information on

/etc/inittab

, see Section 3.5.

Feel free to configure runlevels 2 and 4 as you see fit. Many users configure those runlevels in a way

that makes the most sense for them while leaving the standard runlevels 3 and 5 alone. This allows