-o option
             Can be used to give options in the format used in the configuration file.  This is useful for specifying options for which there is no separate command-line flag.  For
             full details of the options listed below, and their possible values, see ssh_config(5).


[root@netkiller tmp]# ssh root@192.168.2.18
The authenticity of host '192.168.2.18 (192.168.2.18)' can't be established.
RSA key fingerprint is 83:e9:fc:a9:98:6b:33:41:0f:b2:44:13:01:f5:af:3c.
Are you sure you want to continue connecting (yes/no)? 

===>這段話的意思是,無法確認host主機的真實性,只知道它的公鑰md值,問你還想繼續連接嗎?

[root@netkiller tmp]# ssh  -o stricthostkeychecking=no root@192.168.2.18
Warning: Permanently added '192.168.2.18' (RSA) to the list of known hosts.
root@192.168.2.18's password: