There could be a situation where port 80 on your server is already occupied by some other process and therefore you are not able to start a new process / application on port 80. In this situation you may want to close the process running on port 80.
For closing the process on port 80 we use the following commands
nmap is a utlity which lists all the opened ports and the process running on those ports. Using the above command would let you know which ports are occupied on your machine.
You can kill the process running on the port 80 by using the following commands
fuser -k <port>/tcp
In the place of port put the value 80 to close the port 80 on the machine.
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