ERROR 1044 (42000): Access denied for user ''@'localhost' to database 'mysql'

 在网上找了好多资料说是更改root密码，可是更改过后还是问题依旧，于是试着 select * from user;结果发现表为空(Empty set(0.00 sec))；所以考虑增加root用户（比较郁闷，不知用户表怎么空了），步骤如下：

1.关闭mysql
   # service mysqld stop
2.屏蔽权限
   # mysqld_safe --skip-grant-table

3. mysql -u root mysql

 mysql>use mysql ;

4 . mysql>insert into user set user = 'root',ssl_cipher='',x509_issuer='',x509_subject='';
Query OK, 1 row affected, 3 warnings (0.00 sec) 
(这时可能会提示某字段如ssl_cipher无默认值, 只要加上,ssl_cipher=”; 其字段如有提示依次添加就OK了) 


update user set Host='localhost',select_priv='y', insert_priv='y',update_priv='y', Alter_priv='y',delete_priv='y',create_priv='y',drop_priv='y',reload_priv='y',shutdown_priv='y',Process_priv='y',file_priv='y',grant_priv='y',References_priv='y',index_priv='y',create_user_priv='y',show_db_priv='y',super_priv='y',create_tmp_table_priv='y',Lock_tables_priv='y',execute_priv='y',repl_slave_priv='y',repl_client_priv='y',create_view_priv='y',show_view_priv='y',create_routine_priv='y',alter_routine_priv='y',create_user_priv='y' where user='root'; 
 


7 重启mysql 


8 mysql> use mysql;
  mysql> update user set password = password('123456') where user = 'root';

9.退出重进，OK成功！！