ssh是linux的标准配置并且最常用，可以用来判断端口是否打开
用法: ssh -v -p port username@ip
-v 详细模式(会打印日志，显示登录的细节).
-p 指定端口
username 可以随意
ip 待测试机器的ip
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pipci@HP:~$ ssh -v -p 111 dd@10.10.10.6
OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 10.10.10.6 [10.10.10.6] port 111.
debug1: Connection established. ##出现Connection established表示建立连接，也就代表着这个端口开放
debug1: key_load_public: No such file or directory
debug1: identity file /home/pipci/.ssh/id_rsa type -1
省略
pipci@HP:~$ ssh -v -p 222 dd@10.10.10.6
OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 10.10.10.6 [10.10.10.6] port 222.
debug1: connect to address 10.10.10.6 port 222: Connection refused
ssh: connect to host 10.10.10.6 port 222: Connection refused ##出现Connection refused表示连接拒绝，也就代表着这个端口关闭
pipci@HP:~$
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