Port to PID

How do you find which process is listening on a given port? Use the `lsof` command.

For example, I saw that some process was already using port 69 (normally TFTP).

lsof -i :69

To look for http:

lsof -i :80

You can also look for files opened by a given user or command:

lsof -u USER
lsof -c COMMAND