Here is Justin’s top 5 UNIX security books.

Title	Author	ISBN
Practical UNIX and Internet Security	Garfinkel and Spafford	1-56592-148-8
UNIX System Security	David Curry	0-201-60640-2
The UNIX Programming Environment	Kernighan and Pike	0-13-937681-X
UNIX & Linux System Administration Handbook	Nemeth et al	0-13-151051-7
Building Internet Firewalls	O’Reilly and Assoc	1-56592-124-0