SSH Got WARNING: 'POSSIBLE DNS SPOOFING DETECTED'

(ptian) ptian- ssh -l user host_name

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@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @
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The RSA host key for site has changed,
and the key for the according IP address 10.210.23.91
is unknown. This could either mean that
DNS SPOOFING is happening or the IP address for the host
and its host key have changed at the same time.
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@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
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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
b2:58:2f:50:88:18:30:be:fa:5b:7e:56:56:ab:50:e7.
Please contact your system administrator.
Add correct host key in /home/ptian/.ssh/known_hosts to get rid of this message.
Offending key in /home/ptian/.ssh/known_hosts:21
RSA host key for host_name has changed and you have requested strict checking.
Host key verification failed.
(ptian) ptian-

解决方法：编辑器打开/home/ptian/.ssh/known_hosts文件，找到要连接的服务器，并去除那一行，重新ssh