Red Hat ENTERPRISE LINUX 3 Reference Manual page 20

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order of the drives searched while booting is controlled with a setting in BIOS, and it looks on the
master IDE device on the primary IDE bus. The BIOS then loads into memory whatever program is
residing in the first sector of this device, called the Master Boot Record or MBR. The MBR is only 512
bytes in size and contains machine code instructions for booting the machine, called a boot loader,
along with the partition table. Once the BIOS finds and loads the boot loader program into memory,
it yields control of the boot process to it.
1.2.2. The Boot Loader
This section looks at the boot loaders for the x86 platform. Depending on the system's architecture,
the boot process may differ slightly. Refer to Section 1.2.2.1 Boot Loaders for Other Architectures for
a brief overview of non-x86 boot loaders.
When using Red Hat Enterprise Linux, two boot loaders are available: GRUB or LILO. GRUB is the
default boot loader, but LILO is available for those who require or prefer it. For more information
about configuring and using GRUB or LILO, see Chapter 2 Boot Loaders.
Both boot loaders for the x86 platform are broken into at least two stages. The first stage is a small
machine code binary on the MBR. Its sole job is to locate the second stage boot loader and load the
first part of it into memory.
GRUB is the newer boot loader and has the advantage of being able read ext2 and ext3
load its configuration file —
Menu Configuration File for information on how to edit this file.
With LILO, the second stage boot loader uses information on the MBR to determine the boot options
available to the user. This means that any time a configuration change is made or kernel is manually
upgraded, the
/sbin/lilo -v -v
to the MBR. For details about doing this, refer to Section 2.8 LILO.
Tip
If upgrading the kernel using the Red Hat Update Agent, the boot loader configuration file is up-
dated automatically. More information on Red Hat Network can be found online at the following URL:
https://rhn.redhat.com.
Once the second stage boot loader is in memory, it presents the user with a graphical screen showing
the different operating systems or kernels it has been configured to boot. On this screen a user can
use the arrow keys to choose which operating system or kernel they wish to boot and press [Enter]. If
no key is pressed, the boot loader loads the default selection after a configurable period of time has
passed.
Note
If Symmetric Multi-Processor (SMP) kernel support is installed, there will be more than one option
present the first time the system is booted. In this situation, LILO will display
SMP kernel, and
Linux ( kernel-version -smp)
( kernel-version )
1. GRUB reads ext3 file systems as ext2, disregarding the journal file. Refer to the chapter titled The ext3
File System in the Red Hat Enterprise Linux System Administration Guide for more information on the ext3 file
system.
/boot/grub/grub.conf
command must be executed to write the appropriate information
, which is for single processors. GRUB displays
linux-up
, which is the SMP kernel, and
, which is for single processors.
Chapter 1. Boot Process, Init, and Shutdown
— at boot time. Refer to Section 2.7 GRUB
Red Hat Enterprise Linux
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partitions and
, which is the
linux
Red Hat Enterprise