Chapter 5. Boot, Initialization, Shutdown, and Runlevels (Topic 2.6)

Even the most inexpensive PC has a fairly complex series of steps to execute on its way from idle hardware to productive system. When a system is powered on, a computer's electronics are in a random state and must be reset to a known condition. After this occurs, the CPU in the system begins processing instructions at a specific, hardcoded memory location in Read-Only Memory (ROM). For PCs, the ROM is usually called the Basic Input/Output System (BIOS). The startup instructions stored in the BIOS perform basic initialization chores to discover and configure peripheral hardware. When the system is initialized and ready, it begins looking in known locations for an operating system (or operating system loader software). This could be stored on fixed or removable disk media, or even placed in memory during initialization. Once an operating system is launched, it begins an initialization sequence of its own.

This section covers the latter portions of the boot process, from the point where the BIOS looks for an operating system, as required for Exam 101.^[1] This Topic has two Objectives:

^[1] The BIOS is covered in Chapter 13.

Objective 1: Boot the System

This Objective covers the Linux boot process, including boot-time kernel options, examining log file events, and the dmesg and lilo commands. We also examine some boot-related configuration files. Weight: 3.

Objective 2: Change Runlevels and Shutdown or Reboot System

Linux and many Unix systems share the concept of runlevels. A Linux runlevel describes a mode of operation, such as single-user mode or multiuser mode. Runlevels and the associated shutdown and system reboot topics are covered in this Objective. Weight: 3.