Linux mysql 5.6： ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

案例环境：

操作系统 ：Red Hat Enterprise Linux Server release 5.7 (Tikanga) 64 bit

数据库版本 : Mysql 5.6.19 64 bit

案例介绍：

今天开始学习mysql，遂先安装了Mysql 5.6.19 64bit 版本的数据库，结果安装成功了，但是使用root登录时遇到了ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)错误. 如下所示

[root@DB-Server tmp]# rpm -ivh MySQL-server-5.6.19-1.rhel5.x86_64.rpm 

Preparing...                ########################################### [100%]

   1:MySQL-server           ########################################### [100%]

[root@DB-Server tmp]# rmp -ivh MySQL-client-5.6.19-1.rhel5.x86_64.rpm 

-bash: rmp: command not found

[root@DB-Server tmp]# rpm -ivh MySQL-client-5.6.19-1.rhel5.x86_64.rpm 

Preparing...                ########################################### [100%]

   1:MySQL-client           ########################################### [100%]

[root@DB-Server tmp]# /etc/rc.d/init.d/mysql status

MySQL is not running[FAILED]

[root@DB-Server tmp]# /etc/rc.d/init.d/mysql start

Starting MySQL.[  OK  ]

[root@DB-Server tmp]# mysql -u root -p

Enter password: 

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

[root@DB-Server tmp]# mysql -u root mysql

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

安装过程中没有设置过root密码，不清楚root密码，搜索了网上一些资料，大致有下面一些情况：

1：有些博客说root的随机密码位于/root/.mysql_secret中，但是我这个版本根本没有/root/.mysql_secret文件。搜索到一篇文章，大意如下所示（没有确认）。到现在也没有明白，我这个版本为什么没有生成这个文件？

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO) :表示没有生成root的临时密码

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES) :表示生成了root的临时密码。

2：有些资料说root的默认密码为空，经过确认那是以前的老版本，Mysql 5.6及以后版本出处于安全考虑，root密码已经不为空了。

另外，我在官网论坛居然发现有很多人遇到类似问题ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

解决方法：

首先停掉mysql服务器

[root@DB-Server init.d]# /etc/rc.d/init.d/mysql stop

 Shutting down MySQL..[ OK ]

然后使用mysqld_safe命令在启动mysql，更新root账号的密码

--skip-grant-tables：不启动grant-tables(授权表),跳过权限控制。

--skip-networking ：跳过TCP/IP协议，只在本机访问(从网上有些资料看，这个选项不是必须的。可以不用)

[root@DB-Server init.d]# mysqld_safe --user=mysql --skip-grant-tables --skip-networking &

[2] 9396

[root@DB-Server init.d]# 140722 14:59:46 mysqld_safe Logging to '/var/lib/mysql/DB-Server.err'.

140722 14:59:46 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

执行上面命令后，此会话窗口会出现无反应的状态，需要使用CTRL+C中断会话，检查/var/lib/mysql/DB-Server.err日志，发现也无其它异常信息。没有弄明白该会话窗口为啥会出现无响应状态。

tail -200 /var/lib/mysql/DB-Server.err | more

2014-07-22 14:59:41 9346 [Note] Shutting down plugin 'binlog'

2014-07-22 14:59:41 9346 [Note] /usr/sbin/mysqld: Shutdown complete

140722 14:59:41 mysqld_safe mysqld from pid file /var/lib/mysql/DB-Server.pid ended

140722 14:59:46 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

2014-07-22 14:59:47 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timesta

mp server option (see documentation for more details).

2014-07-22 14:59:47 9516 [Note] Plugin 'FEDERATED' is disabled.

2014-07-22 14:59:47 9516 [Note] InnoDB: Using atomics to ref count buffer pool pages

2014-07-22 14:59:47 9516 [Note] InnoDB: The InnoDB memory heap is disabled

2014-07-22 14:59:47 9516 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins

2014-07-22 14:59:47 9516 [Note] InnoDB: Compressed tables use zlib 1.2.3

2014-07-22 14:59:47 9516 [Note] InnoDB: Using Linux native AIO

2014-07-22 14:59:47 9516 [Note] InnoDB: Using CPU crc32 instructions

2014-07-22 14:59:47 9516 [Note] InnoDB: Initializing buffer pool, size = 128.0M

2014-07-22 14:59:47 9516 [Note] InnoDB: Completed initialization of buffer pool

2014-07-22 14:59:47 9516 [Note] InnoDB: Highest supported file format is Barracuda.

2014-07-22 14:59:47 9516 [Note] InnoDB: 128 rollback segment(s) are active.

2014-07-22 14:59:47 9516 [Note] InnoDB: Waiting for purge to start

2014-07-22 14:59:47 9516 [Note] InnoDB: 5.6.19 started; log sequence number 1626087

2014-07-22 14:59:47 9516 [Note] /usr/sbin/mysqld: ready for connections.

Version: '5.6.19'  socket: '/var/lib/mysql/mysql.sock'  port: 0  MySQL Community Server (GPL)

[root@DB-Server init.d]# mysql -u root mysql

Reading table information for completion of table and column names

You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 1

Server version: 5.6.19 MySQL Community Server (GPL)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its

affiliates. Other names may be trademarks of their respective

owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> select Host, User, Password,password_expired

    -> from user

    -> where user='root' and host='root' or host='localhost';

+-----------+------+-------------------------------------------+------------------+

| Host      | User | Password                                  | password_expired |

+-----------+------+-------------------------------------------+------------------+

| localhost | root | *A848DE7CCD839E924921BEE41711991DDA0D529E | Y                |

+-----------+------+-------------------------------------------+------------------+

1 row in set (0.00 sec)

mysql> update user set password=PASSWORD('p12#456')

    -> where user='root' and host='root' or host='localhost';

Query OK, 1 row affected (0.00 sec)

Rows matched: 1  Changed: 1  Warnings: 0

新设置用户或更改密码后需用flush privileges刷新MySQL的系统权限相关表，否则会出现拒绝访问，还有一种方法，就是重新启动mysql服务器，来使新设置生效。

mysql> flush privileges;

Query OK, 0 rows affected (0.00 sec)

mysql> quit

Bye

[root@DB-Server init.d]# /etc/rc.d/init.d/mysql restart

Shutting down MySQL..140722 15:02:27 mysqld_safe mysqld from pid file /var/lib/mysql/DB-Server.pid ended

[  OK  ]

Starting MySQL.[  OK  ]

[2]-  Done                    mysqld_safe --user=mysql --skip-grant-tables --skip-networking

[root@DB-Server init.d]# mysql -u root p

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

[root@DB-Server init.d]# mysql -u root -p

Enter password: 

Welcome to the MySQL monitor.  Commands end with ; or \g.

Your MySQL connection id is 2

Server version: 5.6.19

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its

affiliates. Other names may be trademarks of their respective

owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

另外，如果登录mysql数据库后执行脚本遭遇 ERROR 1820 (HY000): You must SET PASSWORD before executing this statement,可以使用重新设置一次密码即可解决问题.

mysql>set password = password('p12#456'); 

至此问题解决，但是还有不少地方有些疑惑，为啥出现这个错误？ 其实这么多资料都只是说了解决方法，但是都回避了问题的原因。

参考资料：

http://huangyifa163.blog.163.com/blog/static/262875752011127102215790/

http://sundful.iteye.com/blog/704337

http://wenku.baidu.com/view/735ffa41be1e650e52ea995a.html

http://www.cnblogs.com/sunson/articles/2172086.html

http://blog.163.com/eric1945@126/blog/static/164934572201081494343373/

http://www.cnblogs.com/likai198981/archive/2013/04/06/3002518.html