Mostrar Usuarios y roles existentes en postgres

Se utiliza \du

$ sudo su - postgres
$ psql 
postgres=# \du
                           List of roles
 Role name |                   Attributes                   | Member of 
-----------+------------------------------------------------+-----------
 openerp   | Superuser, Create role, Create DB, Replication | {}
 postgres  | Superuser, Create role, Create DB, Replication | {}

postgres=#