Personal computers are no longer as personal as they used to be. You might have a family computer, for example, and each member of the family uses the computer with his own personal account. In this case, at one time or another you will encounter this conversation, or something like it: "I need to use the computer." "But I'm right in the middle of typing my school report." "This can't wait, you need to log off and let me use it now!"
If you are ever caught in a situation in which you have to relinquish control of your computer to another person, it seems both logical and natural that you should close all your applications and log out before allowing the other person to access the computer. That isn't necessary with Linux. Linux is truly multiuser. You can have two or more people logged in to the same computer at the same time, even running separate graphical desktops at the same time. You don't have to close all your applications and log out. All you have to do to relinquish control to another person is to lock your session (for security purposes), and then let the next person start up his own session.
In some cases, desktop environments, such as KDE and GNOME, provide you with a handy menu option that will let someone start another desktop session. If your Linux distribution doesn't provide you with that easy method, don't worry. The following hacks will show you how you can set up two or more KDE or GNOME graphical login screens, where each user can start up her own session isolated from any other sessions that are running.
I've even provided a method for the staunch power user who resists point-and-click in favor of a command-line approach.
Finally, these hacks introduce a whole new approach to graphical login screens. These screens replace the dull text login prompt with a graphical frame-buffer console prompt that lets you start up anything from plain-text consoles to window managers or desktop environments such as KDE and GNOME. You can set up as many of these login screens as you want, and each one will start up a separate user session. You can even customize the graphical look and feel of each login screen.