gap between error and cure

I get an error:

psql: FATAL:  no pg_hba.conf entry for host "[local]", user "postgres", database
"template1"

when I try to run "psql template1" (which I have been doing successfully for
several years)

version 8.4.5 compiled with no switches
centos 5.5

It worked last week, not this week.

I saw a reference to run a command "show hba_file" but there hasn't been any
clue as to WHERE one runs that command.  Please hold my hand.  Which user (root
or postgres) and which program?

Thanks in advance.

jk