И что systemctl unmask может замаскировать несуществующий сервис?
$ sudo systemctl unmask param-pam-pam
$ sudo systemctl unmask param-pam-pam
$ sudo systemctl unmask param-pam-pam
$ sudo systemctl mask param-pam-pam
Created symlink from /etc/systemd/system/param-pam-pam.service to /dev/null.
$ sudo systemctl start param-pam-pam
Failed to start param-pam-pam.service: Unit param-pam-pam.service is masked.