EnvironmentFiles and support for /etc/sysconfig files
The EnvironmentFiles= line in the [Service] section of .service files is used to support loading environment variables that can be used in unit files. For instance, if your sysv-initscript used a file in /etc/sysconfig to set command line options, you can use EnvironmentFiles= like so:
Example:
[Service] Type=forking EnvironmentFile=-/etc/sysconfig/httpd ExecStart=/usr/sbin/httpd $OPTIONS ExecReload=/usr/sbin/httpd $OPTIONS -k restart
You may then refer to variables set in the /etc/sysconfig/httpd file with
${FOOBAR} and $FOOBAR, in the ExecStart=
lines (and related lines). (${FOOBAR} expands the variable into
one word, $FOOBAR splits up the variable value at whitespace into
multiple words)
The "-" on the EnvironmentFile= line ensures that no error messages is generated if the environment file does not exist. Since many of these files were optional in sysvinit, you should include the "-" when using this directive.
Although environment files are easy to use, upstream systemd recommends a different approach. Their recommendation for administrators who need to reconfigure systemd .service files is to copy them from /lib/systemd/system to /etc/systemd/system and modify them there. Unit files in /etc/systemd/system override those in /lib/systemd/system if they otherwise carry the same name.
Either approach is valid in Fedora.