PG roles are stored in the DB, not Unix. You can set up pg_hba to use ident authentication so that users are automatically granted access by their Unix login, b

PG roles are stored in the DB, not Unix. You can set up pg_hba to use ident authentication so that users are automatically granted access by their Unix login, but it isn't the default (and usually not recommended), and you still have to have PG roles in the database for them to correspond to. So I think there's been a misunderstanding.