It's happened to all of us. We're faced with a system we have only limited access to administer, and something is Not Right.
What's to do?
One of PostgreSQL's dustier corners is its built-in administration functions, blessed by all who know about them. You need to have database superuser access to call most of them. As database superuser access is a sine qua non of fixing problems, we assume it's in hand.
Find the pg_hba.conf:
Read its contents:
SELECT * FROM pg_catalog.pg_read_file('pg_hba.conf');
In pre-9.1 versions of PostgreSQL:
WITH f(name) AS (VALUES('pg_hba.conf'))
SELECT pg_catalog.pg_read_file(name, 0, (pg_catalog.pg_stat_file(name)).size) FROM f;
Unfortunately, the pg_stat_file/pg_read_file don't work for pg_hba.conf on Debian (and presumably Ubuntu and other derivatives), where that file is located in /etc/postgresql, i.e., not in the database cluster directory (normally /var/lib/postgresql) or the log directory.
In any case, shouldn't the first select be SELECT * FROM pg_catalog.pg_read_file('pg_hba.conf')?