postgres/contrib/pg_dumpaccounts

pg_dumpaccounts

This is a little utility script derived from pg_dumpall. It just
dumps the global pg_shadow and pg_group as pg_dumpall does without
dumping any of the databases. This is useful for installations 
that have many databases with different backup schedules, where
pg_dumpall will never be run and thus, the users and groups will
never be backed up.