xxxxxxxxxx
$> lsof -wni tcp:3000
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
ruby 51195 shino 10u IPv4 0x3cd31f222cb761f 0t0 TCP 127.0.0.1:hbci (LISTEN)
ruby 51195 shino 11u IPv6 0x3cd31f215db234f 0t0 TCP [::1]:hbci (LISTEN)
# then run kill -9 51195
#replace 51195 with your corresponding PID number