Error: when running rake db:drop on server was prompted with fe_sendauth: no password supplied.

Solution: In config/database.yml, edit the username & password pair for production environment, changing them into the pair that your server produced. In digitalOcean’s case, this info is displayed every time you ssh log in, like this:

You can use the following Postgres database credentials:
  * User: rails
  * Pass: PasSwOrD