Restore Postgresql database from table files
This doesn't sound promising.  Do you know how you got into this predicament?

What specific system tables are empty?  A good chunk of the system catalogs are located inside $PGDATA/base/&lt;db_oid&gt;

Do you have any recent backups that could be used to splice together whatever it is that you are missing?

Of course the first step it to make a backup of the current state of things, so if you somehow make things even worse you can go back and try again.