SELinux is the access control system developed by the NSA. It is a relatively new technology that has been included in the 2.6 kernel. More importantly, SELinux is becoming a central security mechanism in various distributions, including the recently released Red Hat Enterprise Linux 4. Mayer et al. will help the reader to: understand the purpose of the new security technology SELinux brings to Linux; learn the reference for all aspects of SELinux security policy language; manage and maintain security of SELinux-based distributions such as Red Hat REL4; develop and write new SELinux security policy modules; and understand how to use SELinux to build secure systems.