Maintaining a completely secure system is impossible. With diligence, however, it is possible to keep your Linux machines secure enough that most casual crackers, script-kiddies, and other Bad Guys will be thwarted and go bug someone else. Remember that simply following this tutorial will not result in a secure system. Instead, we hope to touch on many of the major topic areas and gives you some useful examples of how to get started.

Linux system security can be divided into two parts: internal security and external security. Internal security refers to guarding against users accidentally or maliciously disrupting the system. External security refers to preventing unauthorized users from gaining access to the system.

This section will cover internal security first, then external security, and we'll finish with some general guidelines and tips.