The Grub Boot Loader; Boot Loaders And System Architecture; Grub; Grub And The X86 Boot Process - Red Hat ENTERPRISE LINUX 4.5.0 Reference Manual

Chapter 2.

The GRUB Boot Loader

When a computer with Red Hat Enterprise Linux is turned on, the operating system is loaded
into memory by a special program called a boot loader. A boot loader usually exists on the
system's primary hard drive (or other media device) and has the sole responsibility of loading
the Linux kernel with its required files or (in some cases) other operating systems into memory.

1. Boot Loaders and System Architecture

Each architecture capable of running Red Hat Enterprise Linux uses a different boot loader. The
following table lists the boot loaders available for each architecture:
Architecture
AMD® AMD64
IBM®eServer™iSeries™
IBM®eServer™pSeries™
IBM®S/390®
IBM®eServer™zSeries®
Intel®Itanium™
x86
Table 2.1. Boot Loaders by Architecture
This chapter discusses commands and configuration options for the GRUB boot loader included
with Red Hat Enterprise Linux for the x86 architecture.

2. GRUB

The GNU GRand Unified Boot loader (GRUB) is a program which enables the selection of the
installed operating system or kernel to be loaded at system boot time. It also allows the user to
pass arguments to the kernel.

2.1. GRUB and the x86 Boot Process

This section discusses the specific role GRUB plays when booting an x86 system. For a look at
the overall boot process, refer to
GRUB loads itself into memory in the following stages:
1. The Stage 1 or primary boot loader is read into memory by the BIOS from the MBR
1
For more on the system BIOS and the MBR, refer to
Section 2, "A Detailed Look at the Boot
Section 2.1, "The
Boot Loaders
GRUB
OS/400®
YABOOT
z/IPL
z/IPL
ELILO
GRUB
Process".
BIOS".
1
. The
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