法一：(telnet)

(1)安装telnet

$: yum install telnet telnet-server -y

$: systemctl start telnet.socket

$: systemctl enable telnet.socket

(2)用法

$:telnet baidu.com 80

Trying 123.125.115.110...

Connected to baidu.com. #出现Connected表示连通了，说明百度的80端口开放的

Escape character is '^]'. #ctrl + ] 退出

(3)写脚本通过telnet检查端口

$: echo -e "\n"|telnet baidu.com 80|grep Connected

Connection closed by foreign host.

Connected to baidu.com.

法二：(nmap)

(1)安装namp

$:yum -y install nmap

(2)使用

$:nmap localhost #查看主机当前开放的端口

$:nmap -p 1024-65535 localhost #查看主机端口(1024-65535)中开放的端口

$:nmap -PS 192.168.21.163 #探测目标主机开放的端口

$:nmap -PS22,80,3306 192.168.21.163 #探测所列出的目标主机端口

$:nmap -O 192.168.21.163 #探测目标主机操作系统类型

$:nmap -A 192.168.21.163 #探测目标主机操作系统类型

$:nmap --help #更多nmap参数请查询帮助信息

(3)写脚本通过nmap检查端口

26 PORT_COUNT=`nmap $ip_add -p $port|grep open|wc -l`

29 [[ $PORT_COUNT -ge 1 ]] && echo "$ip_add $port is ok." || echo "$ip_add $port is unknown."

法三：(通过nc命令检查)

(1)使用

$: nc -w 5 211.100.98.99 80 && echo ok

ok

$: nc -w 10 8.8.8.8 53 && echo ok ||echo no

ok

(2)写脚本通过nc检查端口并监控memcache服务

export oldboyTimestampMemcachedIp=$1

export oldboyTimestampMemcachedPort=$2

export oldboyTitle=NAGIOS

export oldboyTimestampMD5=4ED06F8D41B9264OLD0BOY30BE5212BB7E34

export wwwServerIp=$3

export wwwServerPort=$4

printf "delete $oldboyTimestampMD5\r\n" | nc $oldboyTimestampMemcachedIp $oldboyTimestampMemcachedPort >/dev/null 2>&1

sleep 1

judge=($(printf "HEAD /oldboy/$oldboyTitle HTTP/1.1\r\nHost: $5\r\n\r\n" | nc $wwwServerIp $wwwServerPort | head -n1|tr "\r" "\n"))

参考：《查看远端的端口是否通畅3个简单实用案例！》http://blog.51cto.com/oldboy/942530