Red Hat ENTERPRISE LINUX 3 Reference Manual

Also see for ENTERPRISE LINUX 3 - SECURITY GUIDE: Tuning guide Installation guide Installation guide Installation guide Manual

Contents

Chapter 2.Boot LoadersWhen a computer with Red Hat Enterprise Linux is turned on, the operating system is loaded intomemory by a special program called a boot loader. A boot loader usually exists on the system’sprimary hard drive (or other media device) and has the sole responsibility of loading the Linux kernelwith its required files or (in some cases) other operating systems into memory.2.1. 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 LoadersIBM® eServer™ iSeries™ OS/400®IBM® eServer™ pSeries™ YABOOTIBM® S/390® z/IPLIBM® eServer™ zSeries® z/IPLIntel® Itanium™ ELILOx86 GRUB or LILOAMD64 and Intel® Extended Memory 64 Technology (Intel®EM64T)GRUBTable 2-1. Boot Loaders by ArchitectureThis chapter discusses commands and configuration options for the two boot loaders supplied withRed Hat Enterprise Linux for the x86 architecture: GRUB and LILO.2.2. GRUBGNU 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 argumentsto the kernel.2.2.1. GRUB and the x86 Boot ProcessThis section discusses the specific role GRUB plays when booting an x86 system. For a look at theoverall 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 MBR1. Theprimary boot loader exists on less than 512 bytes of disk space within the MBR and is capableof 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.