Linux - Program / Service on a Specific TCP Port

lsof
Type the following command to see IPv4 port(s), enter:
# lsof -Pnl +M -i4
Type the following command to see IPv6 listing port(s), enter:
# lsof -Pnl +M -i6

netstat
Type the command as follows:
# netstat -tulpn
# netstat -npl