Which command lists all currently loaded service units?

• A. systemctl list-unit-files --type=service
• B. systemctl status --type=service
• C. systemctl show --type=service
• D. systemctl list-units --type=service

Answer: (D)

You're being tested on how to see which systemd units are currently loaded into memory, specifically the service units. The command that lists those loaded units is systemctl list-units with a type filter for services. This command shows you the units that systemd has actively loaded, along with their current state (load, active, and sub state) and a short description. Filtering by type=service ensures you only see service units, not other unit types like sockets or timers.

The other options don’t fit this purpose. Listing unit files shows definitions on disk, not what’s currently loaded in memory. Asking for status or show targets a particular unit (or a set of units) to display details about it, not a comprehensive list of all loaded services. So the command that correctly lists all currently loaded service units is the one that queries the in-memory set of units and restricts the output to services.