O'Reilly - Linux Security Cookbook.  
by Daniel J. Barrett, Robert G. Byrnes, Richard Silverman. 
ISBN : 0-596-00391-9, 332 Pages, June 2003. 

The Linux Security Cookbook includes real solutions to a wide range of targeted problems, such as sending encrypted email within Emacs, restricting access to network services at particular times of day, firewalling a webserver, preventing IP spoofing, setting up key-based SSH authentication, and much more. With over 150 ready-to-use scripts and configuration files, this unique book helps administrators secure their systems without having to look up specific syntax. The book begins with recipes devised to establish a secure system, then moves on to secure day-to-day practices, and concludes with techniques to help your system stay secure.