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Unix/Linux Security 
Other Security Books Linux Administrator's Security Guide
Practical UNIX & Internet Security (S. Garfinkel, G. Spafford) [Mirror] [Mirror] [Mirror] [Mirror] [Mirror] [Mirror]
Linux Security HOWTO (K. Fenzi, D. Wreski) Linux Security for Beginners (Neil A. Smyth)
Linux Firewall Configuration: Packet Filtering and Netfilter/iptables (O. Andreasson) [Mirror]
Securing Debian Linux (J.F. Peņa) Linux Security Administrator's Guide
Securing Linux Production Systems (W. Puschitz) Secure Programming for Linux and Unix (D.A. Wheeler)
Securing and Optimizing Linux: A Hands on Guide, Red Hat Edition (G. Mourani) [PDF]
Getting Started with SELinux (Faye Coker) Guide to Writing SE Linux Policy (Faye Coker)