Raspberry π

For finding an open ssh port on your network

for i in {1,10,20,30,40}; do sudo nmap 192.168.$i.* -p 22 --open; done

(Change the 1, 10 etc... to reflect what subnets you have)

For ports in use on localhost:

lsof -Pn +M -i4

also this, which I use to track down ports that are open & blocking something else :

netstat -anlp | grep -w "Proto\|LISTEN"