Linux boot disks are useful in a number of situations, such as testing a new kernel, recovering from a disk failure (anything from a lost boot sector to a disk head crash), fixing a disabled system, or upgrading critical system files safely (such as libc.so).
There are several ways of obtaining boot disks:
Use one from a distribution such as Slackware. This will at least allow you to boot.
Use a rescue package to set up disks designed to be used as rescue disks.
Learn what is required for each of the types of disk to operate, then build your own.
This document assumes some basic familiarity with Linux system administration concepts. For example, you should know about directories, filesystems and floppy diskettes. You should know how to use mount and df. You should know what /etc/passwd and fstab files are for and what they look like. You should know that most of the commands in this HOWTO should be run as root.
Constructing a bootdisk from scratch can be complicated. If you haven't read the Linux FAQ and related documents, such as the Linux Installation HOWTO and the Linux Installation Guide, you should not be trying to build boot diskettes. If you just need a working bootdisk for emergencies, it is much easier to download a prefabricated one. See Appendix A.1, below, for where to find these.