如果 Server Key 與 ~/.ssh/known_hosts 比對成功， 那麼您就會直接進入等待密碼輸入的畫面， 那就不必每次都得要輸入 (yes/no) 囉～


不過，您或許也會發現一件事情啊，我們知道 SSH server 雖然使用 version 2 已經不會重複製造 server key (public key) 了，但是如果該主機重新安裝過新的 linux distributions 時， 那把 server key 就會被改變啊！而 client 又會去比對這個 public key 與 ~/.ssh/known_hosts ， 此時 Client 就會發現兩者不同了，於是乎產生如下的錯誤訊息了：

[root@linux ~]# <span class="term_command">ssh dmtsai@localhost</span>@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!Someone could be eavesdropping on you right now (man-in-the-middle attack)!It is also possible that the RSA host key has just been changed.The fingerprint for the RSA key sent by the remote host isf8:ae:67:0e:f0:a0:3e:aa:d9:77:19:c9:2e:62:22:72.Please contact your system administrator.Add correct host key in /root/.ssh/known_hosts to get rid of this message.Offending key in /root/.ssh/known_hosts:1RSA host key for localhost has changed and you have requested strict checking.Host key verification failed.

這個錯誤訊息在告訴您，上次所登錄的遠端 SSH 主機的 Keys 已經被改過了(最可能的原因就是 Server 端重新開機/重新安裝/更新套件等等啦！)， 所以無法繼續登入～呵呵！這個時候怎麼辦？很簡單啊！

進入您的家目錄的 ~/.ssh 裡面，編輯一下 known_hosts ，將欲連接的主機名稱的 Key 給他消除，就可以重新連線啦！ 

[root@linux ~]# <span class="term_command">vi ~/.ssh/known_hosts</span><br />localhost ssh-rsa AAAAB3NzaC1yc2Euowireffodjoiwjefmoeiwhoqhwupoi<br />t[egmlomowimvoiweo6VpTHTw2/tENp4U7Wn8J6nxYWP36YziFgxtWu4MPSKaRmr<br />E4eUpR1G/zV3TkChRZY5hGUybAreupTVdxCZvJlYvNiejfijoejwiojfijeoiwx5<br />eRkzvSj7a19vELZ5f8XhzH62E=<br />

上面表格的內容其實是同一行的～那一行代表『 localhost 這部主機，利用的是 ssh-rsa 連線機制， 而後續的資料則是那把 Server Key 的內容。』如果您確定這次的比對無法成功是正常的， 那麼您可以將這一行給他刪除，這樣下次要再登入時，就又會再次的出現問 (yes/no) 的畫面啊！ 

mlzboy@mlzboy-laptop:~$ ssh mao@192.168.0.4 
    
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
    
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @ 
    
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
    
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! 
    
Someone could be eavesdropping on you right now (man-in-the-middle attack)! 
    
It is also possible that the RSA host key has just been changed. 
    
The fingerprint for the RSA key sent by the remote host is 
    
17:9c:ea:7f:03:2b:42:d4:bb:b2:76:47:51:01:ee:ef. 
    
Please contact your system administrator. 
    
Add correct host key in /home/mlzboy/.ssh/known_hosts to get rid of this message. 
    
Offending key in /home/mlzboy/.ssh/known_hosts:3 
    
RSA host key for 192.168.0.4 has changed and you have requested strict checking. 
    
Host key verification failed. 
    
mlzboy@mlzboy-laptop:~$ ssh mao@192.168.0.4 
    
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
    
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @ 
    
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
    
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! 
    
Someone could be eavesdropping on you right now (man-in-the-middle attack)! 
    
It is also possible that the RSA host key has just been changed. 
    
The fingerprint for the RSA key sent by the remote host is 
    
17:9c:ea:7f:03:2b:42:d4:bb:b2:76:47:51:01:ee:ef. 
    
Please contact your system administrator. 
    
Add correct host key in /home/mlzboy/.ssh/known_hosts to get rid of this message. 
    
Offending key in /home/mlzboy/.ssh/known_hosts:3 
    
RSA host key for 192.168.0.4 has changed and you have requested strict checking. 
    
Host key verification failed.

这个错误要注意，它告诉你是在~/.ssh/下的known_hosts的第3行出错了，因此打开这个文件，然后将它删除，之后就可以联上了