[CentOS] postgres 7 - CentOS 4.4

> # sudo -u postgres psql -f central.sql -q FOO foo
> psql: FATAL:  IDENT authentication failed for user "foo"

OK - if i change that line to read

# sudo -u postgres psql -f central.sql -q FOO

that runs fine - So i need to find out from the application people what 
the difference in those 2 commands is

thanks