Running Linux, Third Edition

Booting the System

There are several ways of booting Linux on your system. The most common methods involve booting from the hard drive or using a boot floppy. In many cases, the installation procedure will have configured one or both of these for you; in any case, it’s important to understand how to configure booting for yourself.

Using a Boot Floppy

Traditionally, a Linux boot floppy simply contains a kernel image, which is loaded into memory when the floppy is booted on the system.^[14] The kernel image is usually compressed, using the same algorithm as the gzip compression program (more on this in Section 7.4.2 in Chapter 7). Compression allows the kernel, which may be a megabyte or more in size, to require only a few hundred kilobytes of disk space. Part of the kernel code is not compressed: this part contains the routines necessary to uncompress the kernel from the disk image and load it into memory. Therefore, the kernel actually “bootstraps” itself at boot time by uncompressing into memory.

A number of parameters are stored in the kernel image. Among these parameters is the name of the device to use as the root filesystem once the kernel boots. Another parameter is the text mode to use for the system console. All of these parameters may be modified using the rdev command, which we’ll discuss later in the section.

After the kernel has started, it attempts to mount a filesystem on the root device hard-coded in the kernel image itself. This will serve as the root filesystem—that ...