Access denied for user 'root'@'localhost' (using password: no)

Access denied for user 'root'@'localhost' (using password: no)

       sudo /etc/init.d/mysqld stop      //关闭mysql
       mysqld_safe --user=mysql --skip-grant-tables --skip-networking &    
       mysql -u root mysql
       mysql> UPDATE user SET Password=PASSWORD('你想要的密码') where USER='root';
       mysql> FLUSH PRIVILEGES;
       mysql> quit
       sudo /etc/init.d/mysqld start
       mysql -uroot -p 你的密码