SELinuxs

SELinux (Security-Enhanced Linux) is a Linux kernel security module that implements mandatory access control (MAC) using policy-based confinement to restrict how processes interact with files, sockets, and other resources. It aims to enforce least-privilege behavior, reducing the impact of software vulnerabilities. SELinux was originally developed by the U.S. National Security Agency (NSA) in collaboration with researchers and has been integrated into major Linux distributions such as Red Hat Enterprise Linux, Fedora, and Debian.

The core concept of SELinux is the security policy, which assigns labels or contexts to every subject (process) and object (file, directory, socket). A policy governs the allowed interactions between labeled subjects and objects, typically using Type Enforcement (TE) as the primary mechanism. Policies can be loaded as modules and customized; the most common is the targeted policy, which confines a subset of services while leaving most of the system unconfined. More expansive policies, including Multi-Level Security (MLS) and RBAC-based policies, exist but are used less widely.

SELinux supports multiple operating modes: enforcing, where policy violations are denied and logged; permissive, where violations are only logged; and disabled. Administrators manage SELinux through a range of tools and settings, such as getenforce and setenforce to query and switch modes, semanage and setsebool to adjust policy behavior, and restorecon (along with file labeling commands) to apply correct file contexts. AVC denials are recorded in audit logs and can be analyzed with standard audit utilities.

Adoption of SELinux provides strong containment for servers and compliance-oriented environments, but it requires careful policy management and proper labeling to avoid unintended service disruptions.