After vito failure to install postgres (9.1) in Ubuntu 12.04

what_i_did.sh

# when I tried to start postgres, I had an error telling me there were no postgres clusters created
# so I had to create one using the `pg_createcluster` command, like the following
pg_createcluster 9.1 main --start

#after creating the cluster, it will start the server because of `--start`
#so I had to change to postgresql user
sudo su - postgres

#to change it's pasword, doing `psql -d <database_name> -U <username>
psql -d postgres -U postgres

#inside psql, I did
\password postgres

#so psql will ask for new password