The book is an introduction to the internal structure of the Linux operating system. All provisions are clearly illustrated with examples developed by the author and tested in practice. The main kernel subsystems and their essences are considered - files and file systems, virtual memory and mapped files, processes, threads and means of interprocess communication, pipes, sockets and shared memory. Discretionary and mandatory (compulsory) access control mechanisms, as well as process privileges, are disclosed. The user environment and CLI, X Window systems and GUI, as well as the network subsystem and SSH service are described in detail. Particular attention is paid to the command interpreter language and its use to automate tasks of operating the operating system. The second edition added new chapters describing the Wayland graphical system, containers, virtualization and the functioning of Linux as a unified system of all its components, taking into account changes in the latest versions of the OS, and also wishes and reviews from readers.