here is the one I was having,

http://stackoverflow.com/questions/12472988/postgres-could-n...

postgres app fixed it

> I suppose osx built-in installation may cause conflicts.

This is a consistent source of trouble when installing Postgres. Usually, this involves looking up the right places to modify the path and sometimes needing to change permissions/ports.

To be honest I've spent about 4 hours last week trying to install homebrew PostgreSQL on a friends MacBook ... it took me forever to figure out why it wasn't connecting to the right socket, just because he had some things out of date :\

While it is really easy to install most of the time, I'd say the Postgres.app works well for people who aren't developers but need to use PostgreSQL.

Did you see the post installation instructions to initialize a db?

initdb /usr/local/var/postgres -E utf8

Also if you are working with rails, add host: localhost in your database.yml file and remove the user password. That should be all you need.