Port to PID
See all listening ports and their associated PIDs with `netstat`
The '--inet' option will show only ipv4 sockets. Replace '--inet' with '--udp --tcp' to show both ipv4 and ipv6 sockets.
netstat --listening --program --inet --numeric-hosts --numeric-ports --extend
See whp is using a specific port with `lsof`
Use the `lsof` command to find which process is listening on a given port.
The -n option for `lsof` turns of reverse name resolution which speeds up the output. Otherwise it will try to reverse each IP address to a name.
There are security limitation to the use of `lsof` by non-root users. These limitations depend on how `lsof` was compiled. In general you have to be root or have sudo to use these examples.
For example, say I saw that some process was already using port 69 (normally TFTP). I did not expect this port to be in use, so I ran the following command to find out which process what listening on port 69:
sudo lsof -n -i :69
To find which process is listening on port 80 (you would expect an HTTP server):
sudo lsof -n -i :80
To see who is connected or listening on SSH or SCP look for port 22:
sudo lsof -n -i :22
You can also look for files opened by a given user or command:
sudo lsof -n -u USER
sudo lsof -n -c COMMAND