Operation Manual
17
Booting and Conguring a
Linux System
Booting a Linux system involves different components. The hardware itself is initialized
by the BIOS, which starts the Kernel by means of a boot loader. After this point, the
boot process with init and the runlevels is completely controlled by the operating system.
The runlevel concept enables you to maintain setups for everyday usage as well as to
perform maintenance tasks on the system.
17.1 The Linux Boot Process
The Linux boot process consists of several stages, each represented by a different
component. The following list briey summarizes the boot process and features all the
major components involved.
1. BIOS After turning on the computer, the BIOS initializes the screen and keyboard
and tests the main memory. Up to this stage, the machine does not access any mass
storage media. Subsequently, the information about the current date, time, and the
most important peripherals are loaded from the CMOS values. When the rst hard
disk and its geometry are recognized, the system control passes from the BIOS to
the boot loader.
2. Boot Loader The rst physical 512-byte data sector of the rst hard disk is loaded
into the main memory and the boot loader that resides at the beginning of this sector
takes over. The commands executed by the boot loader determine the remaining part
of the boot process. Therefore, the rst 512 bytes on the rst hard disk are referred
to as the Master Boot Record (MBR). The boot loader then passes control to the ac-
Booting and Conguring a Linux System 233