Why SELinux Matters: How It Works and When (Not) to Disable It

What Is SELinux?

SELinux is a security‑enhanced Linux kernel module that enforces mandatory access control (MAC) policies written by security analysts. It controls which subjects (processes, programs) may access which objects (files, devices), providing a higher level of protection than standard discretionary permissions.

How SELinux Works

The kernel checks the policy each time a process attempts to access an object. Both processes and objects are labeled (e.g., a:b:c). Access is granted only when the labels match the rules defined in the policy, optionally considering MLS hierarchies.

Disabling SELinux can expose the system to serious threats; it should only be done for a justified reason, not merely for convenience.

Drawbacks of Disabling SELinux

When SELinux is disabled, processes behave like on a regular Linux system, losing the protection against privilege abuse. Compromised root‑owned processes could read confidential files, and the system becomes more vulnerable to attacks.

Strict policies can cause operational pain—for example, files owned by root with mode 000 prevent legitimate programs from running, and debugging applications may be hindered by SELinux denials.

A practical compromise is to use “permissive” mode: SELinux remains enabled but logs policy violations instead of enforcing them, allowing you to observe what would be blocked.

How to Disable SELinux on CentOS and Similar Distributions

Step 1: Open the configuration file /etc/selinux/config (or its symlink /etc/sysconfig/selinux).

Step 2: Change the line SELINUX=enforcing to SELINUX=disabled.

Step 3: Reboot the system, or apply the change for the current session with setenforce 0; the change takes effect after reboot.