Mysql2::Error - Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2): code example

Example 1: can't connect to local mysql server through socket '/tmp/mysql.sock' (2)

Try to start the MySQL server:
mysql.server start

Example 2: Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

ln -s /private/var/mysql/mysql.sock /tmp/mysql.sock