The book is an introduction to the internal structure of the Linux operating system. All provisions are clearly illustrated by examples developed by the author and tested by him in practice. The main subsystems of the kernel and their essence are considered - files and file systems, virtual memory and displayed files, processes, threads and means of interprocess, interaction, channels, sockets and shared memory. Disclosed are discretionary and mandatory (forced) access control mechanisms, as well as process privileges. The CLI user environment and command line interface, 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 the tasks of operating the operating system.