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SELinux Management

What Is SELinux

SELinux, short for Security-Enhanced Linux, is a security module that provides an extra layer of protection to Linux-based systems. It enforces mandatory access control (MAC) policies on the system by controlling how processes and users access files, directories, and other resources.

SELinux was initially developed by the United States National Security Agency (NSA) and is now an open-source project. It has been integrated into many Linux distributions, including Red Hat Enterprise Linux (RHEL), Fedora, CentOS, and others.

SELinux operates by applying security contexts (also called labels) to files, processes, and users. These contexts consist of user identities, roles, types (or domains), and optional MLS/MCS levels (for multi-level or multi-category security). By defining and enforcing strict rules based on these contexts, SELinux can limit the potential damage caused by malicious programs or unauthorized users.

SELinux policies dictate the rules governing access control. These policies are usually written in a high-level language called Common Intermediate Language (CIL) and compiled into a binary format that the kernel can understand. The most common policy provided by Linux distributions is the "targeted" policy, which focuses on securing network-facing services and confining user activities.

SELinux has three operational modes:

Enforcing: In this mode, SELinux enforces the security policy by denying access based on the policy rules. Any access violations are logged.
Permissive: In this mode, SELinux does not enforce the security policy, but logs any policy violations. This mode is helpful for troubleshooting and policy development.
Disabled: In this mode, SELinux is turned off, and the system operates without its security enhancements.

SELinux adds an extra layer of security to Linux systems, making it more difficult for attackers to exploit vulnerabilities and compromise the system. However, it also requires proper configuration and management to ensure the desired level of protection.