systemd: How to unmask a service whose unit file is empty?

A service unit that is empty (0 bytes) will be parsed by systemd as masked. While systemctl mask <unit> 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.

8 comments and no answer - really guys, focus on the question. How to unmask a systemd service!!!! You can try systemctl unmask your_app.service , but if your service link has been symlinked to /dev/null, this will fail. The following is the recommended process:

1. Check that the unit file is a symlink to /dev/null:

   file /lib/systemd/system/your_app.service
   OR
   file /etc/systemd/system/your_app.service
   

   It should return:

   /lib/systemd/system/your_app.service: symbolic link to /dev/null
   

2. Delete the symlink:

   sudo rm /lib/systemd/system/your_app.service
   

3. Reload systemd daemon as you changed a service:

   sudo systemctl daemon-reload
   

4. Check the status:

   systemctl status your_app
   

Happy Hosting :)