How can the nc command be used to test UDP ports in Linux?

To test a UDP port using the nc command, you can enter the following command in the terminal:

nc -u <IP地址> <端口号>

The -u option represents using the UDP protocol, is the target IP address to test, and is the target port number to test.

For example, to test the UDP port 1234 on your local host, you can execute the following command:

nc -u localhost 1234

If the UDP port is open and the local host can connect to that port, you will see an output similar to the following:

Connection to localhost 1234 port [udp/*] succeeded!

If the UDP port is closed, or if there are firewall or other obstacles on the network path, you may see output similar to the following:

nc: connect to localhost port 1234 (udp) failed: Connection refused

Please note that the nc command may not be a default installation option for all Linux distributions. You may need to install the nc command line tool, for example, by running the following command on Debian/Ubuntu:

sudo apt-get install netcat

You can also run the following command to install on CentOS/RHEL:

sudo yum install nc

Please choose the appropriate command for installation based on the Linux distribution you are using.