Recently I was doing some work with RoR and needed to reset my password for the postgres that ships with OSX (9.1 it seems).

This turned into a challenge finding a simple set of instructions!

Editing the hba file

sudo vi /Library/PostgreSQL/9.1/data/pg_hba.conf

File should be modified so that the first line changes ‘md5’ to ‘trust’ to avoid it prompting for the current password.

# "local" is for Unix domain socket connections only
local all all trust  #was 'md5'

Then you need to Postgres:

$ sudo su - postgres
$ cd /Library/PostgreSQL/9.1/bin
$./pg_ctl restart -m fast -D /Library/PostgreSQL/9.1/data

Then you need to reconnect with the psql client and change the password:

./psql

And from the psql client, run the following statement:

WARNING: psql version 9.0, server version 9.1.
Some psql features might not work.
Type "help" for help.

postgres=# ALTER USER postgres with password 'yourpassword';