lsof command is used to list open files. This includes listing
network connections. This means I can check if a particular port is in use
and what process is using that port. For instance, I can check if my rails
application is currently running on port 3000.
$ lsof -i TCP:3000 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME ruby 13821 jb 12u IPv6 0xdf... 0t0 TCP localhost:hbci (LISTEN) ruby 13821 jb 13u IPv4 0xdf... 0t0 TCP localhost:hbci (LISTEN)
I can see that a ruby process (my rails app) is using port 3000. The PID and a number of other details are included.
See more details with