最近在做mysql 多实例的时候，采用不同的方式登录mysql数据库，发现mysql -uroot -p -h 127.0.0.1 -P3308 ，登录时居然不要密码就可以登录，吓得我一身汗，经过检查终于找到原因记录下来，给小白们参考。

[root@mysql ~]# mysql -uroot -p -S /data/3308/mysql.sock

Enter password:          #需要输入密码

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

Your MySQL connection id is 23

Server version: 5.5.32-log Source distribution

Copyright (c) 2000, 2013, 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 current_user();

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

| current_user() |

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

| root@localhost |

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

1 row in set (0.00 sec)

*******************************************************************

[root@mysql ~]# mysql -uroot -p -h 127.0.0.1 -P3308

Enter password:  #不需要输入密码，直接回车登录

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

Your MySQL connection id is 24

Server version: 5.5.32-log Source distribution

Copyright (c) 2000, 2013, 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>

mysql> select  current_user();

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

| current_user() |

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

| root@127.0.0.1 |

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

1 row in set (0.00 sec)

不要密码登录原因：

登录数据库查看密码

mysql> select user,host,password from mysql.user;

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

| user | host      | password                                  |

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

| root | localhost | *FE28814B4A8B3309DAC6ED7D3237ADED6DA1E515 |

| root | mysql     |                                           |

| root | 127.0.0.1 |                                           |

| root | ::1       |                                           |

|      | localhost |                                           |

|      | mysql     |                                           |

| tom  | %         | *71FF744436C7EA1B954F6276121DB5D2BF68FC07 |

| tom1 | %         | *36B46F2410B8A8E6E1DC6952C5C26929FDC07421 |

| tom2 | %         | *FEF6FE64F2588DC11E69F0DC5A704E231D1AAEFC |

| tom  | localhost | *71FF744436C7EA1B954F6276121DB5D2BF68FC07 |

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

10 rows in set (0.00 sec)

总结：第一种方式登录后，用户是 root@localhost，第二种方式登录后，用户是root@127.0.0.1 查看数据库，发现root@localhost没有设置密码，所以使用第一种方式登录不需要输入密码。