Access denied for user ''@'localhost' to database 'mysql'

1.关闭mysql

   # service mysqld stop
2.屏蔽权限
   # mysqld_safe --skip-grant-table
   屏幕出现： Starting demo from .....
3.新开起一个终端输入
   # mysql -u root mysql
   mysql> delete from user where USER='';
   mysql> FLUSH PRIVILEGES;//记得要这句话，否则如果关闭先前的终端，又会出现原来的错误

   mysql> \q

from: http://www.cnblogs.com/Anker/p/3551610.html