Red Hat LINUX 7.2 Reference Manual page 42

42
initiates a login process for that user. This allows users to authenticate themselves to the system and
begin to use it.
Also, /etc/inittab tells init how it should handle a user hitting
sole. As Red Hat Linux should be properly shut down and restarted rather immediately power-cycled,
init is told to execute the command /sbin/shutdown -t3 -r now when a user hits those
keys. In addition, /etc/inittab states what init should do in case of power failures, if your
system has a UPS unit attached to it.
In runlevel 5, /etc/inittab runs a script called /etc/X11/prefdm. The prefdm script runs
the preferred X display manager (gdm if you are running GNOME or kdm if you are running KDE
based on the contents of the /etc/sysconfig/desktop directory.
At this point, you should be looking at a login prompt. All that, and it only took a few seconds.
3.2.3 SysV Init
As we have seen, the init program is run by the kernel at boot time. It is in charge of starting all the
normal processes that need to start up with the system. These include the getty processes that allow
you to log in, NFS daemons, FTP daemons, and anything else you want to run when your machine
boots.
SysV init is the standard init process in the Linux world to control the startup of software at boot time,
because it is easier to use and more powerful and flexible than the traditional BSD init.
SysV init also differs from BSD init in that the configuration files are in /etc/rc.d instead of
residing directly in /etc. In /etc/rc.d, you will find rc, rc.local, rc.sysinit, and the
following directories:
init.d
rc0.d
rc1.d
rc2.d
rc3.d
rc4.d
rc5.d
rc6.d
SysV init represents each of the init runlevels with a separate directory, using init and symbolic links
in each of the directories to actually stop and start the services as the system moves from runlevel to
runlevel.
In summary, the chain of events for a SysV init boot is as follows:
• The kernel looks in /sbin for init
• init runs the /etc/rc.d/rc.sysinit script
Chapter 3:Boot Process, Init, and Shutdown
- - at the con-
[Ctrl] [Alt] [Delete]