Content One: Occupy system local ports manually
# startport=33000;endport=34000;for i in $(seq $startport $endport);do nc -lk $i &;done(Add: Take start port is 33000 and end port is 34000 as an example here)
Content Two: Release all ports which are opened manually (kill all nc command processes)
# for i in $(ps -aux | grep nc | grep '\-lk' | awk '{print $2}');do kill $i; done