Discover How To Harden My Filesystem HOWTOs
RSBAC - Rule Set Based Access Control
RSBAC is a flexible, powerful and fast open source access control framework for current Linux kernels, which has been in stable production use since January 2000 (version 1.0.9a). All development is independent of governments and big companies, and
Lud's Linux Corner
You will find security tips to improve your overall system security by the use of IPChains, IPTables, and TCP Wrappers. And you will learn some useful and subtle configuration options for Sendmail, Postfix, Bind, NFS and others.
linsec TWiki
linsec TWiki is a web-based collaboration tool for a personal project detailing security on Linux in particular, but any *NIX-ish operating system (ie. OpenBSD, Mac OS X, etc.).
Knocker
Knocker is a simple and easy to use TCP security port scanner written in C to analyze hosts and all of the different services started on them.
Kismet
Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and can sniff 802.11b, 802.11a, and 802.11g traffic.
John the Ripper password cracker
John the Ripper is a fast password cracker, currently available for many flavors of Unix (11 are officially supported, not counting different architectures), DOS, Win32, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords.