Two-Minute Drill

Here are some of the key points from the certification objectives in Chapter 3.

The BIOS Initialization Sequence

❑	While not strictly a part of the exam, it's important to know the basics of the BIOS.
❑	You can change the boot sequence from the BIOS menu.
❑	Once the BIOS detects your drives, it hands control to GRUB via the master boot record (MBR).

The GRUB Boot Loader

❑	GRUB, the GRand Unified Boot loader, is the default for RHEL 5.
❑	Errors in the GRUB configuration file can lead to a number of boot problems, including kernel panics.
❑	You can read the GRUB configuration file from the GRUB command line.

Kernel Initialization and the First Process

❑	You can analyze how the kernel booted your system through /var/log/dmesg.
❑	As the kernel initializes your system, it loads important modules such as the ext3 filesystem.

The First Process and /etc/inittab

❑	Once the kernel boots, it hands control to init, also known as the First Process.
❑	The init process starts your system as configured in /etc/inittab.
❑	One of the key configuration files started by the First Process is /etc/rc.sysinit.

Runlevels

❑	There are six different runlevels available; the default is configured in /etc/ inittab.
❑	Don't configure a default runlevel of 0 or 6.
❑	The default runlevel configured in /etc/inittab starts scripts in the associated /etc/rcx.d directory, where x is the runlevel.
❑	You can boot to the runlevel of your choice from the GRUB configuration menu.
❑	Study the /etc/rc.d hierarchy and the /etc/inittab and /etc/rc.d/rc.sysinit files. This is the key to understanding what's happening during the boot process.

Controlling Services

❑	The chkconfig command gives you a simple way to maintain the /etc/rc.d directory structure.
❑	The ntsysv and system-config-services commands provide console and GUI tools for the same purpose.

System Configuration Files

❑	There are a number of non-network configuration files in the /etc/sysconfig directory.
❑	You can edit many of these files directly or use GUI tools, which you can start with commands such as system-config-date, system-config-keyboard, and system-config-services.