[GENERAL] listing users and their rights

[Thomas T. Thai]

as a pgsql superuser, how can i list all the users and their rights? on
mysql i just do a select on the mysql table. i'm a newbie here. i read the
documents and didn't find the answer.

also, when i start 'psql' as system user joe, it says:

psql: FATAL 1:  Database "joe" does not exist in the system catalog.

if i run psql as system user XXX it would say '... Database "XXX" does not
exist...'

from the documents, it seems as though i can start psql without specifying
a database.