mysql> use mysql
ERROR 1044 (42000): Access denied for user 'root'@'localhost' to database 'mysql'
mysql> exit
Bye
[root@testtest ~]# service mysqld stop
Stopping mysqld:                                           [  OK  ]
[root@testtest ~]# mysqld_safe --user=mysql --skip-grant-tables --skip-networking &

[root@testtest ~]# mysql -u root -p -hlocalhost
Enter password:

mysql> use mysql

mysql> SELECT host,user,password,Grant_priv,Super_priv FROM mysql.user;

mysql> UPDATE mysql.user SET Grant_priv='Y', Super_priv='Y' WHERE User='root';

mysql> FLUSH PRIVILEGES;

mysql> GRANT ALL ON *.* TO 'root'@'localhost';

mysql> GRANT ALL ON *.* TO 'root'@'cn.cn.cn.cn';

mysql> GRANT ALL ON *.* TO 'root'@'245.245.245.245';

mysql> GRANT ALL ON *.* TO 'root'@'127.0.0.1';

mysql> FLUSH PRIVILEGES;

mysql> quit
Bye
[root@testtest ~]# service mysqld start

restart Linux/OS