By default, SELinux is enabled automatically on new Oracle Linux installations.

Linux security has historically been based on a Discretionary Access Control (DAC) policy, which provides minimal protection from broken software or from malware that's running as a normal user or as root. Access to files and devices is based solely on user identity and ownership. Malware or misconfigured software can do anything with files and resources that the user that started the process can do. If the user is root or the application is setuid or setgid to root, the process can have root-access control over the entire file system.

The National Security Agency created Security Enhanced Linux (SELinux) to provide a finer-grained level of control over files, processes, users, and applications on Linux. The SELinux enhancement to the Linux kernel implements the Mandatory Access Control (MAC) policy, which can be used to define a security policy that provides granular permissions for all users, programs, processes, files, and devices. The kernel's access control decisions are based on all the security relevant information available, and not solely on the authenticated user identity.

When security-relevant access occurs, such as when a process tries to open a file, SELinux intercepts the operation at the kernel level. The operation only continues if a MAC policy rule allows it, otherwise SELinux blocks the operation and returns an error to the process. The kernel checks and enforces DAC policy rules before MAC rules, so it doesn't check SELinux policy rules if DAC rules have already denied access to a resource.

For more details about SELinux, including task-related information, see Oracle Linux: Administering SELinux.

See also the SELinux Project Wiki and the selinux(8) manual page.