SElinux is one of the 4 or so security modules in the Linux kernel. Examples are SELinux, Smack, Tomoyo, and AppArmor. There is also a "capabilities" security

SElinux is one of the 4 or so security modules in the Linux kernel. Examples are SELinux, Smack, Tomoyo, and AppArmor. There is also a "capabilities" security module that can be used in conjunction with the aforementioned modules. Each distribution will have a preferable default security module. To my knowledge the NSA have not rolled their own Linux distribution, but they were the folks that initially created SELinux to meet their needs for a mandatory access control system that has parity to their security clearance structure. Redhat then modified it to make it easier to use by adding concepts such as "unconfined" users and types as well as targeted policies, meaning that if it does not match a rule, it is not enforced. Even with the changes implemented by Redhat many people still disable SELinux rather than making rules to fit all of their custom deployments.