本地连接时，通过localhost不能登陆到指定的端口

本地连接时，通过localhost不能登陆到指定的端口

朋友说他的一台服务器上，装了多个mysql,用了不同的端口，通过localhost的方式指定端口时，连上的还是3306的端口

mysql -uroot -hlocalhost  -P3307 -p

这样连的是 3306的库。

但是通过

mysql -uroot -h127.0.0.1 -P3307 -p

连到的是 3307的库。

这是为什么

我在我本地一台服务器上建了两个实例，  3306和3308

mysql -uroot -h127.0.0.1 -P3308

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

Your MySQL connection id is 2

Server version: 5.5.24 Source distribution

Copyright (c) 2000, 2011, 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 user,host from mysql.user;

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

| user | host       |

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

| root | 10-4-1-104 |

| root | 127.0.0.1  |

| root | ::1        |

| root | localhost  |

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

 mysql -uroot --host=localhost -P3308

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

这种方式，直接就连不上。

查看了文档  5.6 p264

On Unix, MySQL programs treat the host name localhost specially, in a way that is likely different from

what you expect compared to other network-based programs. For connections to localhost, MySQL

programs attempt to connect to the local server by using a Unix socket file. This occurs even if a --port

or -P option is given to specify a port number. To ensure that the client makes a TCP/IP connection to the

local server, use --host or -h to specify a host name value of 127.0.0.1, or the IP address or name of

the local server. You can also specify the connection protocol explicitly, even for localhost, by using the

--protocol=TCP option.

当使用localhost的时候，会试着用socket文件，虽然你指定了端口。

指定--protocol=TCP 可以避免这种情况。

在我的环境中：

 mysql -uroot -hlocalhost -P3308 --protocol=TCP

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

Your MySQL connection id is 3

Server version: 5.5.24 Source distribution

Copyright (c) 2000, 2011, 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> show variables like '%port%'

    -> ;

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

| Variable_name       | Value |

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

| innodb_support_xa   | ON    |

| large_files_support | ON    |

| port                | 3308  |

| report_host         |       |

| report_password     |       |

| report_port         | 3308  |

| report_user         |       |

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

告诉朋友，让他加上 --protocol=TCP 之后，也可以正常的连接到想连接的端口

总结：在本地使用localhost登陆库时，如果需要连接到别的端口需要 加上--protocol=TCP