What is the correct location for SYSTEMD units that have been installed with the distribution?

The correct location for systemd units that have been installed with the distribution is typically the directory found at /usr/lib/systemd/system/. This directory is designated for systemd unit files that are provided by the operating system or distribution. These unit files define the services, sockets, timers, and other components that systemd manages.

Systemd unit files located in this directory are considered part of the base system and are generally maintained by package managers when software is installed or updated. It is the standard place for service units that are non-custom and provided by the distribution.

Other directories mentioned have specific uses. For instance, /run/systemd/system/ is a runtime directory for unit files that are created and used by the system during operation. This includes transient units that are generated dynamically, making it unsuitable for units installed with the distribution itself. The /etc/systemd/system/ directory is used for overriding or supplementing the unit files located in /usr/lib/systemd/system/—this is where custom or user-defined units might reside. Lastly, /var/lib/systemd/system/ is not a standard directory used for storing systemd unit files and typically does not contain any relevant units in common usage.

Hence, understanding the purpose of each directory clarifies why /