配置如下：
socket = /data/mysql/data/mysql.sock //套接字文件
在数据库没有任何连接的情况下，可以看到3306端口和socket端口都在监听
mysql@t3-dtpoc-dtpoc-web04 bin$ netstat -an | grep -i 3306
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN
mysql@t3-dtpoc-dtpoc-web04 bin$ netstat -an |grep -i /tmp/mysql.sock
unix 2 ACC STREAM LISTENING 1958079570 /tmp/mysql.sock
窗口1：
mysql@t3-dtpoc-dtpoc-web04 bin$ ./mysql -protocol=socket -uroot -p
窗口2:
mysql@t3-dtpoc-dtpoc-web04 bin$ ./mysql -protocol=socket -uroot -p
可以看到多了两个socket连接，但是3306端口没有连接
mysql@t3-dtpoc-dtpoc-web04 bin$ netstat -an | grep -i 3306
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN
mysql@t3-dtpoc-dtpoc-web04 bin$ netstat -an |grep -i /tmp/mysql.sock
unix 2 ACC STREAM LISTENING 1958079570 /tmp/mysql.sock
unix 3 STREAM CONNECTED 1959434943 /tmp/mysql.sock
unix 3 STREAM CONNECTED 1959434940 /tmp/mysql.sock
mysql@t3-dtpoc-dtpoc-web04 bin$
窗口3：指定IP连接
mysql@t3-dtpoc-dtpoc-web04 bin$ ./mysql -u root -p -h 127.0.0.1
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.7.26-log MySQL Community Server (GPL)
Copyright (c) 2000, 2019, 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.
可以看到3306端口已连接
mysql@t3-dtpoc-dtpoc-web04 bin$ netstat -an | grep -i 3306
tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:45010 127.0.0.1:3306 ESTABLISHED
tcp 0 0 127.0.0.1:3306 127.0.0.1:45010 ESTABLISHED
mysql@t3-dtpoc-dtpoc-web04 bin$ netstat -an |grep -i /tmp/mysql.sock
unix 2 ACC STREAM LISTENING 1958079570 /tmp/mysql.sock
unix 3 STREAM CONNECTED 1959434943 /tmp/mysql.sock
unix 3 STREAM CONNECTED 1959434940 /tmp/mysql.sock