In which mode does SELinux restrict access based on policy rules?

SELinux operates in a mode known as "Enforcing," which is the correct answer. In this mode, SELinux actively enforces the defined security policies on the system. It restricts access to resources by evaluating all operations against the policy rules that govern the behavior of processes and users. If an operation violates these rules, SELinux denies access and logs the event for review. This helps in maintaining a higher level of security by ensuring that only authorized actions are permitted according to the established security context.

In contrast, the "Permissive" mode allows all operations while logging any violations against the policy rules. This mode is useful for troubleshooting and developing policies but does not provide the same level of security as the enforcing mode. The "Disabled" mode completely turns off SELinux, meaning no policies are enforced at all, which significantly diminishes security. Lastly, "Active" is not a recognized mode in the context of SELinux; the modes are specifically Enforcing, Permissive, and Disabled. Therefore, understanding that Enforcing mode is the one that actively restricts access based on security policies is essential for managing system security effectively.