You may have previous experience with MS-DOS or other single user operating systems, such as OS/2 or the Macintosh. In these operating systems, you didn't have to identify yourself to the computer before using it; it was assumed that you were the only user of the system and could access everything. Well, Unix is a multi-user operating system--not only can more than one person use it at a time, different people are treated differently.
To tell people apart, Unix needs a user to identify him or herself by a process called logging in. You see, when you first turn on the computer, several things happen. Since this guide is geared towards Linux, I'll tell you what happens during the boot-up sequence.
Please note that if you're using on some type of computer besides an Intel PC, some things in this chapter won't apply to you. Mostly, they'll be in Section 3.1.1 and Section 3.1.2. (Some parts of Section 3.1.2 will pertain.)