Computer security is an ongoing process, a constant contest between system administrators and intruders. It needs to be monitored carefully and revised frequently. So . . . how the heck can this complex subject be condensed into a bunch of cookbook recipes?
Let's get one thing straight: this book is absolutely not a total security solution for your Linux computers. Don't even think it. Instead, we've presented a handy guide filled with easy-to-follow recipes for improving your security and performing common tasks securely. Need a quick way to send encrypted email within Emacs? It's in here. How about restricting access to your network services at particular times of day? Look inside. Want to firewall your web server? Prevent IP spoofing? Set up key-based SSH authentication? We'll show you the specific commands and configuration file entries you need.
In short: this book won't teach you security, but it will demonstrate helpful solutions to targeted problems, guiding you to close common security holes, and saving you the trouble of looking up specific syntax.