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Learn how linux can see if the port is open? This problem may be often seen in our daily study or work. I hope you can gain a lot from this article. Here is the reference content brought by the editor. Let's take a look at it!

Linux method to check whether the port is open: first open the port and switch root user login; then use the [lsof-I:] port number command line; finally, use the [netstat-aptn] command line to check all the open port numbers.

Operating environment of this tutorial: windows7 system, linux7.3 version, DELL G3 computer

Linux's method to check whether the port is open:

1. First, let's open the command interface of the Linux that you want to view the port, as shown in the figure (take the Ubuntu system as an example)

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

3. The first method is to use the lsof-I: Port number command line, taking 80 as an example, as shown in the figure

4. If there is no output, the port number is not opened. To facilitate testing, I detect an open port number here, and the information shown in the figure will be output.

5. The second way is to use the netstat-aptn command line to check all the open port numbers

6. The command shown in the figure is to check all the port numbers in the system that use the udp protocol.

7. Then this command is to view the port number information of the system using the tcp protocol.

8. Finally, there is a client test method, which is to use the Telnet ip port number command, but I did not test successfully in the virtual machine Linux. I did not know what was going on in the remote Linux system.

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