This book shows how to significantly strengthen the security of the Linux operating system and eliminate existing vulnerabilities of installed applications. You will learn how SELinux works, how you can customize it to suit your needs and use it to strengthen the security of virtualization systems that include libvirt technology (sVirt) and Docker containerization. It also discusses control actions that can improve the security of a particular system using access control enforcement, a security strategy that has defined Linux security for many years. Most of the capabilities of the security system are discussed using real examples. The book is intended for administrators of the Linux operating system, whose task is to manage its security.