A. Security-Enhanced Linux (SELinux) is security patch applied to Linux kernel. When enabled in the kernel it follows the the principle of least privilege. It is an implementation of mandatory access control using Linux Security Modules (LSM).
From Wikipeidia Selinux page:
Security-enhanced Linux is a set of patches to the Linux kernel and some utilities to incorporate a strong, flexible mandatory access control (MAC) architecture into the major subsystems of the kernel. It provides a mechanism to enforce the separation of information based on confidentiality and integrity requirements, which allows threats of tampering and bypassing of application security mechanisms to be addressed and enables the confinement of damage that can be caused by malicious or flawed applications. It includes a set of sample security policy configuration files designed to meet common, general-purpose security goals.
But how do I turn it off or disable SELinux enforcement?
Selinux can be disabled by passing kernel boot parameters. You need to open grub.conf (menu.lst) or lilo.conf and append selinux=0:
For example here is my sample grub.conf file:
title Debian GNU/Linux, kernel 2.6.13-web100 Default
kernel /boot/vmlinuz-2.6.13-web100 root=/dev/hdb1 ro selinux=0
Save file and reboot Linux system. Another option is use setenforce command