代替telnet的测端口通畅的命令
$nc -zv 127.0.0.1 80
Connection to 127.0.0.1 port 80 [tcp/arepa-cas] succeeded! # 成功
nc: connectx to 127.0.0.1 port 80 (tcp) failed: Connection refused # 失败
$nc -zv 127.0.0.1 80
Connection to 127.0.0.1 port 80 [tcp/arepa-cas] succeeded! # 成功
nc: connectx to 127.0.0.1 port 80 (tcp) failed: Connection refused # 失败