Find listening network ports


To obtain a list of all the open ports of your system and which are the associated applications to them just execute command:

netstat -tulp ip or nmap -sT -O ip

9 may 2022 update:

As @rogierm points out, netstat is obsolete and its replacement is ss.

Then the equivalent command to with ss would be:

$ sudo ss -tulp

You can read more about this topic here:

difference between netstat and ss in linux?