After resolving the problem of MySQL and mysql gem I got another problem: MySQL 5.5.8 didn’t start automatically when I boot my computer.
Don’t be serious, you can fix it easily by modifying mysql.server file.
Open /usr/local/mysql/support-files/mysql.server with your favorite text editor, locate the configuration of basedir= and datadir=, change them to:
and the problem gone, your MySQL server now starts automatically everytime you boot the computer.
now you can start the MySQL server manually (no need to reboot) by this command: