SELinux usage in enforcing and permissive modes

Security-Enhanced Linux (SELinux) was introduced in December of 2000 via the Linux-Kernel mailing list as a product started by the National Security Agency (NSA) to improve the security of the operating system by means of mandatory access controls and role-based access control, as opposed to the traditional discretionary access controls that were available in the system.

Before SELinux was introduced in the Linux kernel, discussions took place regarding the proper way to do it, and finally, a kernel framework named Linux Security Modules (LSM) was introduced and SELinux was implemented using it so that other approaches could use LSM, too, and not just SELinux.

SELinux provides security improvements to Linux as access to files made by users, processes, or even other resources can be controlled in a very granular way.

Let's take one example to make it clearer when SELinux comes into play: when a web server is serving pages...