Boot Loaders; Boot Loaders And System Architecture; Grub - Red Hat ENTERPRISE LINUX 3 Reference Manual

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.

2.1. 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
IBM® eServer™ iSeries™
IBM® eServer™ pSeries™
IBM® S/390®
IBM® eServer™ zSeries®
Intel® Itanium™
x86
AMD64 and Intel® Extended Memory 64 Technology (Intel®
EM64T)
Table 2-1. Boot Loaders by Architecture
This chapter discusses commands and configuration options for the two boot loaders supplied with
Red Hat Enterprise Linux for the x86 architecture: GRUB and LILO.

2.2. GRUB

GNU GRand Unified Boot loader or GRUB is a program which enables the user to select which in-
stalled operating system or kernel to load at system boot time. It also allows the user to pass arguments
to the kernel.
2.2.1. 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 Section 1.2 A Detailed Look at the Boot Process.
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
primary boot loader exists on less than 512 bytes of disk space within the MBR and is capable
of loading either the Stage 1.5 or Stage 2 boot loader.
1. For more on the system BIOS and the MBR, refer to Section 1.2.1 The BIOS.
Chapter 2.

Boot Loaders

Boot Loaders

OS/400®
YABOOT
z/IPL
z/IPL
ELILO
GRUB or LILO
GRUB
1
. The