The systemd project is the basic user-space building block used to construct a modern Linux OS. The main daemon, systemd, is the first process started by the kernel, and it brings up the system and acts as a service manager. This article shows how to start a daemon under systemd, describes the supervision and management capabilities that systemd provides, and shows how they can be applied to turn a simple application into a robust and secure daemon. It is a common misconception that systemd is somehow limited to desktop distributions. This is hardly true; similarly to the Linux kernel, systemd supports and is used on servers and desktops, but it is also in the cloud and extends all the way down to embedded devices. In general it tries to be as portable as the kernel. It is now the default on new installations in Debian, Ubuntu, Fedora/RHEL/CentOS, OpenSUSE/SUSE, Arch, Tizen, and various derivatives.
