尝试登录3308端口
[root@lzl mysql]# mysql -P 3308 -uroot -poracle
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 23
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, 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> show variables like '%port%';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| innodb_support_xa | ON |
| large_files_support | ON |
| port | 3306 |
| report_host | |
| report_password | |
| report_port | 3306 |
| report_user | |
| require_secure_transport | OFF |
+--------------------------+-------+
8 rows in set (0.15 sec)
看上去是登陆了，但是登进去发现是端口是3306
感觉很奇怪，--help查看了-P确实是指定端口的
加个空格试下
[root@lzl mysql]# mysql -uroot -poracle -P 3308
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 25
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, 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 | 3306 |
| report_host | |
| report_password | |
| report_port | 3306 |
| report_user | |
| require_secure_transport | OFF |
+--------------------------+-------+
8 rows in set (0.00 sec)
还是3306
后来想到可能是socket的问题，指定socket登陆
[root@lzl mysql]# mysql -uroot -poracle -P 3308 -S/tmp/mysql3308.sock
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 | |
| require_secure_transport | OFF |
+--------------------------+-------+
8 rows in set (0.00 sec)
登陆成功！！！
试一下不指定port，仅指定socket
[root@lzl mysql]# mysql -uroot -p -S/tmp/mysql3308.sock
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, 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 | |
| require_secure_transport | OFF |
+--------------------------+-------+
8 rows in set (0.00 sec)
mysql>
也可以
问题：为什么当我-P指定端口3308时登陆3306？
当我指定-P3308时，mysql去找了默认的socket /tmp/mysql.sock，这个socket是我3306的，于是就登陆了3306。
总结：
1.mysql登陆有2种方式，socket和tcp/ip。
2.socket一般都是本地登陆使用，socket是本地文件，每个mysql实例一个socket。比如mysql -uroot -poracle这样，默认不指定socket的话用的是/tmp/mysql.sock这个文件。只要不指定-h，都会用socket方式登录
3.还有一种方式是tcp/ip，一般都是远程登陆使用。只要指定-h host，mysql就会使用tcpip去登陆数据库。即使是本机指定-h，也是tcp/ip登陆
所有我做了些实验：
如果从远程登陆，应该是直接指定-P port即可，不需要指定socket的
[root@lzl ~]# mysql -h192.168.43.6 -P3308 -uroot -poracle
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, 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 | |
| require_secure_transport | OFF |
+--------------------------+-------+
8 rows in set (0.06 sec)
mysql>
所以，现在有2种方式登录3308端口数据库
mysql -hlocalhost -P3308 -uroot -poracle
mysql -S/tmp/mysql3308.sock -uroot -poracle