1. Create script

Sometimes we need to make sure, that some particular daemon is running on some port, and for that reasons, we can use a simple script:

lsof -nP -i4TCP:$PORT

Don’t forget to replace $PORT with your custom value, like 80.

Let’s see how it works.

I have Nginx up and running on port 80, so I can check that like this:

lsof -nP -i4TCP:80

And the output will be like this:

COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
nginx   68074 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68077 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68078 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68079 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68080 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68081 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68082 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68083 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)
nginx   68084 user   10u  IPv4 0x7e97088702084797      0t0  TCP *:80 (LISTEN)

2. Add function to ~/.bash_profile

2.1. Open bash profile:

nano ~/.bash_profile

2.2. At the end of the file add:

wholisten_tcp() {
   lsof -nP -i4TCP:$1;
}

2.3. Press “Ctrl-O” to save changes.

2.4. Reload .bash_profile:

source ~/.bash_profile

2.5. To use it, now you can just call:

wholisten_tcp 80

Enjoy )).