What is the main location for systemd units that are controlled by the system administrator?

The primary location for systemd units that are managed by the system administrator is the /etc/systemd/system directory. This directory is specifically designed for unit files that override or extend the default configurations found in other directories, such as /usr/lib/systemd/system or /lib/systemd/system. By placing unit files in /etc/systemd/system, administrators can customize service behavior without modifying the original files provided by the OS installation or installed packages.

This organizational structure allows the system to prioritize user-defined configurations, making it easier for administrators to manage services and apply custom settings. Any unit files located in /etc/systemd/system will take precedence over those in the other system directories. This structured approach promotes best practices in system management, ensuring that local modifications remain intact even after updates to the system files.