Security-Enhanced Linux (SELinux) is a Linux kernel security module that provides the mechanism for supporting access control security policies, including United States Department of Defense-style mandatory access controls (MAC). It is a set of kernel modifications and user-space tools that can be added to various Linux distributions. Its architecture strives to separate enforcement of security decisions from the security policy itself and streamlines the volume of software charged with security policy enforcement. The key concepts underlying SELinux can be traced to several earlier projects by the United States National Security Agency.