Systemctl

systemd Unit File Search Paths and Override Precedence

A systemd service file does not have to live in /etc/systemd/system. The system manager searches several directories for unit files, and the directory matters because the search order defines which definition wins when the same unit name exists in more than one place. For an administrator-managed service, /etc/systemd/system is usually the appropriate location. Distribution packages normally install units under /usr/lib/systemd/system, while /run/systemd/system is used for runtime configuration that disappears after reboot. This separation lets local configuration override vendor defaults without editing files owned by the package manager.