How to check whether a specified port is open in Linux

First we open the command operation interface of Linux where we want to view the port, as shown in the figure (taking Ubuntu system as an example)

Then in order to obtain higher permissions (view all ports), switch to root user login here

The first method is to use lsof -i:port No. command line, taking 80 as an example, as shown in the figure:

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If there is no output, it means that the port number is not enabled. To facilitate testing, I will detect an open port number here, and the information as shown in the figure will be output

The second method is to use the netstat -aptn command line to view all open port numbers.

The command shown in the picture is to view all open port numbers in the system. Port number using udp protocol

Then this command is to view the port number information using tcp protocol in the system

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