Warning: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) in /var/www/html/rgbook/config.php3 on line 12

Warning: MySQL Connection Failed: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) in /var/www/html/rgbook/config.php3 on line 12
Unable to connect to database