netstat -nupl | grep 3306 #这个表示查找处于监听状态的，端口号为3306的进程
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Premise: First of all, you must know that the port does not exist independently, it is attached to the process. When a process is opened, its corresponding port is opened; when the process is closed, the port is closed. If a process is opened again next time, the corresponding port will also be opened again. Don't purely understand it as closing a certain port, but you can disable a certain port.
1. You can use "netstat -anp" to check which ports are open.
(Note: Adding parameter '-n' will convert the application to port display, that is, an address in digital format, such as: nfs->2049, ftp->21, so it can be turned on Two terminals, one by one corresponding to the port number corresponding to the program)2. Then you can use "lsof -i:$PORT" to view the program that uses the port ($PORT refers to the corresponding port Number). Or you can also check the file /etc/services to find out the service corresponding to the port.
(Note: Some ports cannot be found through netstat. A more reliable method is "sudo nmap -sT -O localhost")3. To close a certain port port, you can:
1) Disable the port through the iptables tool, such as:iptables -A INPUT -p tcp --dport $PORT -j DROP iptables -A OUTPUT -p tcp --dport $PORT -j DROP
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