ABSTRACT
This chapter describes the uses of systemd for an ordinary user and overviews of systemd components and commands. It explains systemd units and unit files, with an emphasis on service unit files, systemd target unit files, and their purposes and uses. Systemd is, on the surface, a combined Linux initialization program and service manager, that also includes many additional important system state control programs and utilities. After the boot and start-up processes are over and the system is in a steady state, the main purpose of systemd is to maintain that steady state by efficiently and expediently managing system services and processes. One of the fundamental purposes of an initialization, and start-up system such as systemd, is to initialize the components that must be started after the Linux kernel is booted. These components are traditionally known as "userland" components. The chapter covers the following commands and primitives: systemctl, journalctl, systemd unit files, and systemd targets.
