SELinux stands for Security Enhanced Linux, which is an access control system that is built into the Linux kernel. It is used to enforce the resource policies that define what level of access users, programs, and services have on a system.
In its default enforcing mode, SELinux will deny and log any unauthorized attempts to access any resource. This approach, usually referred to as the principle of least privilege, means that explicit permission must be given to a user or program to access files, directories, sockets, and other services.
To learn more about how to use SELinux please read our article, “An Introduction to SELinux on CentOS 7.”
For a more in-depth description of how to define and use SELinux policies, visit the CentOS Wiki page on SELinux.