Understanding service units
Service units are the equivalent of init scripts on old SysV systems. We'll use them to configure our various services, which we used to call daemons in the old days. A service can be pretty much anything that you want to start automatically and run in the background. Examples of services include Secure Shell, your web server of choice, a mail server, and various services that are required for proper system operation. While some service files can be short and sweet, others can be fairly lengthy, with more options enabled. To read about all of these options, just type the following:
man systemd.directives
The descriptions for all of the parameters that you can set are spread over several different man pages. This systemd.directives man page is an index that will direct you to the proper man page for each parameter.
Rather than trying to explain every parameter that service files can use, let's look through a few example files and explain...
