What Chapters 7, 8, and 9 of this book have in common is that they deal with various ways to authenticate users on your network. All three also use Pluggable Authentication Modules (PAM). Rather than spread my PAM instructions throughout these three chapters, I felt it best to give you comprehensive instructions about PAM in a separate appendix. If you already know PAM, and can use the earlier chapters, you probably don't need to read this section.
I also briefly described using Linux as a desktop operating system in several places. Though this book isn't meant to give you thorough instruction in the deployment, maintenance, and use of a Linux desktop, I felt it prudent to include further information on this subject in Appendix B. This material is especially complementary to Chapters 11 and 12.