Find in use ports

Find what program is using a port

lsof -i :8080

Prints

COMMAND     PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node      22208 user   20u  IPv4 0xc276a8f2b74737c2      0t0  TCP localhost:appserv-http (LISTEN)
node      22208 user   24u  IPv4  0xc3478a4e25fbb40      0t0  TCP localhost:appserv-http->localhost:61372 (ESTABLISHED)
Google    93247 user   41u  IPv4 0xf270b3b647faf5ad      0t0  TCP localhost:61372->localhost:appserv-http (ESTABLISHED)

Find all in use ports:

lsof -i -P -n

Only TCP on a port

lsof -i TCP:8080