What command undoes the effects of the mask command on designated units?

The command that undoes the effects of the mask command on designated units is "systemctl unmask." When a service or unit is masked in systemd, it is rendered inoperable, which means that it cannot be started or enabled. Masking is a way to prevent unintentional use of a service. Using "systemctl unmask" removes this restriction, allowing the service to be started or enabled again.

This command is particularly useful when you want to re-enable a service that has been intentionally disabled through masking. By running "systemctl unmask ", you restore the service's ability to be manipulated through the usual commands like start, stop, enable, and disable. This reflects the flexibility of systemd as a service manager, allowing administrators to manage the operational state of their services effectively.

The other options relate to different systemd functionalities. Enabling a service allows it to start at boot time, restoring a unit does not exist in the context of systemd, and removing addresses unit files but does not directly relate to unmasking. Therefore, "systemctl unmask" clearly stands out as the correct command to undo masking effects.