1 For more on the system BIOS and the MBR, refer to Section 2.1, “The BIOS”.The GRUB Boot LoaderWhen a computer with Red Hat Enterprise Linux is turned on, the operating system is loadedinto memory by a special program called a boot loader. A boot loader usually exists on thesystem's primary hard drive (or other media device) and has the sole responsibility of loadingthe Linux kernel with its required files or (in some cases) other operating systems into memory.1. Boot Loaders and System ArchitectureEach architecture capable of running Red Hat Enterprise Linux uses a different boot loader. Thefollowing table lists the boot loaders available for each architecture:Architecture Boot LoadersAMD® AMD64 GRUBIBM®eServer™iSeries™ OS/400®IBM®eServer™pSeries™ YABOOTIBM®S/390® z/IPLIBM®eServer™zSeries® z/IPLIntel®Itanium™ ELILOx86 GRUBTable 2.1. Boot Loaders by ArchitectureThis chapter discusses commands and configuration options for the GRUB boot loader includedwith Red Hat Enterprise Linux for the x86 architecture.2. GRUBThe GNU GRand Unified Boot loader (GRUB) is a program which enables the selection of theinstalled operating system or kernel to be loaded at system boot time. It also allows the user topass arguments to the kernel.2.1. GRUB and the x86 Boot ProcessThis section discusses the specific role GRUB plays when booting an x86 system. For a look atthe overall boot process, refer to Section 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 MBR1. TheChapter 2.13
