systemd: How to unmask a service whose unit file is empty? I tried to start `wpa_supplicant.service`, but I got the following error: > Failed to start wpa_supplicant.service: Unit wpa_supplicant.service is masked. I tried unmasking it using `systemctl unmask wpa_supplicant.service`, but it doesn't seem to change anything. systemctl status wpa_supplicant.service returns > Loaded: masked (/usr/lib/systemd/system/wpa_supplicaant.service; masked; vendor preset: disabled) Active: inactive (dead) What seems really strange is that when I check the `wpa_supplicant.service` file it's an empty document. How can I unmask the service?

A service unit that is empty (0 bytes) will be parsed by `systemd` as masked. While `systemctl mask ` works by symlinking the service to `/dev/null`, systemd appears to just check if a file is 0 bytes when read to determine if a unit is masked. This results in the misleading message about a masked service.
You need to figure out why the service unit is empty.

As to how to unmask a service whose unit file is empty... You "unmask" the service by making the unit non-empty, which is going to be dependent on _why_ the unit is empty.