title: How do I break an arbitrary TCP/IP connection on Linux?
body: <p>Is there any command that can be used to break an existing TCP/IP connection from some program? </p>
  
  <p>Is there anything in a TCP connection the OS is aware of, or do the OS only see TCP transfer on local sockets and doensn't know which request is served to which socket?</p>
  
  <p>For example, if Firefox sends a request to some server's port 80 and is waiting for the answer. Is it possible then to find Firefox listening port and trick Firefox into showing <code>ERR_CONNECTION_REFUSED</code> or something similar.</p>
  
  <p>I would like a solution that does not prevent the data flow and lets the application handle this situation in its way, but rather close the socket or the TCP/IP connection (which should be possible as the socket is something the OS is responsible for I think? Is the connection also a OS property or just something the application does?) so the application would react immediately.</p>