Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 55)

Chapter 3.

Boot Process, Init, and Shutdown

This chapter contains information on what happens when you boot or shut down your Red Hat Linux

system.

Note

This chapter focuses on LILO, the default boot loader for Red Hat Linux 7.1 and earlier versions.

However, Red Hat Linux 7.3 contains an additional boot loader, GRUB, which is discussed thoroughly

in Chapter 4. For more information concerning GRUB, see Chapter 4.

3.1. Introduction

One of the most powerful aspects of Red Hat Linux concerns its open method of starting and stopping

the operating system, where it loads speciﬁed programs using their particular conﬁgurations, permits

you to change those conﬁgurations to control the boot process, and shuts down in a graceful and

organized way.

Beyond the question of controlling of the boot or shutdown process, the open nature of Red Hat

Linux makes it much easier to determine the exact source of most problems associated with start-

ing up or shutting down your system. An understanding of this process is quite beneﬁcial for basic

troubleshooting.

3.2. Behind the Scenes of the Boot Process

Note

This section looks at the x86 boot process, in particular. Depending on your system’s architecture,

your boot process may be slightly different. However, once the kernel is found and loaded by the

system, the default Red Hat Linux boot process is identical across all architectures. Please see

Section 3.7 for more information on a non-x86 boot process.

When a computer is booted, the processor looks at the end of the system memory for the Basic

Input/Output System (BIOS) and runs it. The BIOS program is written into read-only permanent

memory and is always available for use. The BIOS provides the lowest level interface to peripheral

devices and controls the ﬁrst step of the boot process.

The BIOS tests the system, looks for and checks peripherals, and then looks for a drive to use to

boot the system. Usually, it checks the ﬂoppy drive (or CD-ROM drive on many newer systems) for

bootable media, if present, and then it looks to the hard drive. The order of the drives used for booting

is usually controlled by a BIOS setting on the system. Once Red Hat Linux is installed on a hard drive

of a system, the BIOS looks for a Master Boot Record (MBR) starting at the ﬁrst sector on the ﬁrst

hard drive, loads its contents into memory, and passes control to it.

This MBR contains instructions on how to load the boot loader, GRUB or LILO (LInux LOader)

depending on the boot loader you installed. The MBR then loads the boot loader, which takes over

the process (if the boot loader is installed in the MBR). In the default Red Hat Linux conﬁguration,

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 55