Summary of methods to check whether the port is open in Linux

Method 1: Use lsof command

We can use the lsof command to check whether a port is open. The basic syntax is as follows:

lsof -i:port number

If there is no output, it means that the port number is not open.

The following figure takes port 80 and port 53 as an example to check whether port 80 and port 53 are open

You can also use the lsof -i command to directly output the open ports to check whether certain ports are open.

Method 2: Use the netstat command

The netstat command can provide network-related information about a host.

We can check the open ports in linux using netstat -atu

Netstat Flags We Use: -a, -t and -u Introduction

-a: All sockets.

-t : TCP connection of the program

-u: UDP connection for the program

You can also add the -p flag to display the associated PID of the process or program name.

To display only UDP ports, you can use the following command:

To display only TCP ports, you can use the following command: