sh-4.1# nc -w 5 baidu.com 80 && echo ok
ok
sh-4.1# nc -w 5 baidu.com 81 sh-4.1# echo $? 1 sh-4.1# nc -w 5 baidu.com 80 sh-4.1# echo $? #返回上面命 0
telnet 查看端口是否开启：
sh-4.1# telnet baidu.com 84 Trying 111.13.101.208... telnet: connect to address 111.13.101.208: Connection timed out
百度开了80，而并没开84所以，连84端口失败
sh-4.1# telnet baidu.com 80 Trying 123.125.114.144... Connected to baidu.com. Escape character is \'^]\'.