Nowadays, most of the Linux distribution systems such as Fedora, Ubuntu, Arch Linux, Debian, openSUSE, and so on, have switched from
init to systemd. systemd is the first process that gets started after system boot-up with PID 1. It controls and manages other processes that should be started after the system boot-up. It is also known as basic building block for an operating system. To learn about an init-based system, refer to the Wikipedia link at https://en.wikipedia.org/wiki/Init.
systemd has several units, each containing a configuration file with information about a service, socket, device, mount point, swap file or partition, start-up target, and so on.
The following table explains some of unit files:
File extension ...