[root@hzswtb2-mpc ~]# mysql
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
遇到：ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
网上找了很多的文章还是没有解决我的问题；
1.首先可以确认的是mysql 命令行 sql命令关键字是不区分大小写；在mysql 5.1.51版本；
2.先将正常启动的mysqld stop掉；
3.再以绕过root口令检查的方式 启动 mysqld；
4.查询 user 表，发现user表是空的，insert 一个 root 用户， 关闭mysqld，正常启动mysqld，用root用户，新的密码 newpass 就可以登录 mysql shell 了
以下是解决经过：
1.先将正常启动的mysqld stop掉
[root@hzswtb2-mpc ~]# service mysqld stop
Stopping mysqld: [ OK ]
2.用绕过root口令检查的方式 启动 mysql 服务器，并且让其在后台运行；
[root@hzswtb2-mpc ~]# mysqld_safe --user=mysql --skip-grant-tables --skip-networking &
[1] 25513
[root@hzswtb2-mpc ~]# 141215 15:00:16 mysqld_safe Logging to '/var/log/mysqld.log'.
141215 15:00:16 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
3. mysql回车，进入mysql shell，按照前人留下的方法， update user表中的 root 用户的密码，结果发现 0 rows affected，再select 细看 user 表是空的；
[root@hzswtb2-mpc ~]# mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.1.51 Source distribution
mysql> UPDATE user SET PASSWORD=PASSWORD('123456') where USER='root';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 0 Changed: 0 Warnings: 0
mysql> use mysql
Database changed
mysql> show tables;
+---------------------------+
| Tables_in_mysql |
+---------------------------+
| columns_priv |
| db |
| event |
| func |
| general_log |
| help_category |
| help_keyword |
| help_relation |
| help_topic |
| host |
| ndb_binlog_index |
| plugin |
| proc |
| procs_priv |
| servers |
| slow_log |
| tables_priv |
| time_zone |
| time_zone_leap_second |
| time_zone_name |
| time_zone_transition |
| time_zone_transition_type |
| user |
+---------------------------+
23 rows in set (0.00 sec)
mysql> select * from user;
Empty set (0.00 sec)
4.在user表 insert 一个名称为root的用户；
mysql> insert into user(Host,User,Password,Select_priv,Insert_priv) VALUES('localhost','root',PASSWORD('pass3'),'Y','Y');
Query OK, 1 row affected, 3 warnings (0.00 sec)
5.看到有个root用户了；
mysql> select * from user
-> ;
+-----------+------+-------------------------------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+------------+--------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+
| Host | User | Password | Select_priv | Insert_priv | Update_priv | Delete_priv | Create_priv | Drop_priv | Reload_priv | Shutdown_priv | Process_priv | File_priv | Grant_priv | References_priv | Index_priv | Alter_priv | Show_db_priv | Super_priv | Create_tmp_table_priv | Lock_tables_priv | Execute_priv | Repl_slave_priv | Repl_client_priv | Create_view_priv | Show_view_priv | Create_routine_priv | Alter_routine_priv | Create_user_priv | Event_priv | Trigger_priv | ssl_type | ssl_cipher | x509_issuer | x509_subject | max_questions | max_updates | max_connections | max_user_connections |
+-----------+------+-------------------------------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+------------+--------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+
| localhost | root | *35B5E90BC4F5AE5D02ED515DF6B61141F24EDA02 | Y | Y | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | N | | | | | 0 | 0 | 0 | 0 |
+-----------+------+-------------------------------------------+-------------+-------------+-------------+-------------+-------------+-----------+-------------+---------------+--------------+-----------+------------+-----------------+------------+------------+--------------+------------+-----------------------+------------------+--------------+-----------------+------------------+------------------+----------------+---------------------+--------------------+------------------+------------+--------------+----------+------------+-------------+--------------+---------------+-------------+-----------------+----------------------+
1 row in set (0.00 sec)
6 再更新 root 用户的密码，也能返回成功了；
mysql> UPDATE user SET Password = PASSWORD('newpass') WHERE user = 'root';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)
mysql> exit
7.stop 刚才的 mysql服务，以正常方式重新启动mysql 服务器，mysql -u root -p 密码是newpass
[root@hzswtb2-mpc ~]# service mysqld stop
141215 16:12:24 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended
Stopping mysqld: [ OK ]
[1]+ Done mysqld_safe --user=mysql --skip-grant-tables --skip-networking
[root@hzswtb2-mpc ~]# service mysqld start
Starting mysqld: [ OK ]
[root@hzswtb2-mpc ~]#
[root@hzswtb2-mpc ~]# mysql
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
[root@hzswtb2-mpc ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.1.51 Source distribution
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This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
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