This part of the book provides a basic introduction to UNIX host security. These chapters are intended to be accessible to both users and system administrators.

• Chapter 3, Users and Passwords, is about UNIX user accounts. It discusses the purpose of passwords, explains what makes good and bad passwords, and describes how the crypt () password encryption system works.

• Chapter 4, Users, Groups, and the Superuser, describes how UNIX groups can be used to control access to files and devices. It also discusses the UNIX superuser and the role that special users play.

• Chapter 5, The UNIX Filesystem, discusses the security provisions of the UNIX filesystem and tells how to restrict access to files and directories to the file's owner, to a group of people, or to everybody on the computer system.

• Chapter 6, Cryptography, discusses the role of encryption and message digests in your security. It includes a discussion of how various popular encryption schemes, including the PGP mail package, work.