UNIX and Linux Daemon Port Bindings

One of the features of the powerful lsof tool allows for the discovery of a daemon’s port bindings. To examine them, simply issue the following command in the terminal.

lsof -nP -i

One may use the grep command to parse the output as seen in the below example.

lsof -nP -i | grep cupsd

Example output:

cupsd   2865 root 4u  IPv4  8075   TCP 127.0.0.1:631 (LISTEN)
cupsd   2865 root 6u  IPv4  8078   UDP *:631

Above we see that the cupsd process (PID 2865) is bound to TCP 631 and UDP 631.