linux see used ports

# Any of the following
sudo lsof -i -P -n | grep LISTEN
sudo netstat -tulpn | grep LISTEN
sudo lsof -i:22 # see a specific port such as 22
sudo nmap -sTU -O IP-address-Here

sudo lsof -i:22

sudo netstat -tulpn | grep LISTEN

sudo lsof -i:22 # see a specific port such as 22

netstat -tulpn

## if you use linux
sudo ss -tulw