3.7.8 Modifying systemd Configuration Files

If you want to change the configuration of systemd, copy the service, target, mount, socket or other file from /usr/lib/systemd/system to /etc/systemd/system and edit this copy of the original file. The version of the file in /etc/systemd/system takes precedence over the version in /usr/lib/systemd/system, and is not overwritten when you update a package that touches files in /usr/lib/systemd/system. To make systemd revert to using the original version of the file, either rename or delete the modified copy of the file in /etc/systemd/system.