$ sudo mysql -u root # I had to use "sudo" since is new installation
mysql> USE mysql;
mysql> CREATE USER 'YOUR_SYSTEM_USER'@'localhost' IDENTIFIED BY ''; # replace YOUR_SYSTEM_USER with your username
mysql> GRANT ALL PRIVILEGES ON *.* TO 'YOUR_SYSTEM_USER'@'localhost'; # replace YOUR_SYSTEM_USER with your username
mysql> UPDATE user SET plugin='auth_socket' WHERE User='YOUR_SYSTEM_USER'; # replace YOUR_SYSTEM_USER with your username
mysql> FLUSH PRIVILEGES;
# this is the password you need to add to in congfig/database.yml