ssh 접속하려는데,

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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.

자꾸만 이런 에러가 나면서 접속이 안됐다.
http://ubuntuforums.org/archive/index.php/t-598100.html 를 봤지만, 설명이 있는건지 모르겠고, 눈에 잘 안들어오더라.
그러다가 mac os x에서 문제 해결법을 보고 마찬가지 방법으로 고쳤다.
~/.ssh/knownhost 파일을 지우고,
깔끔하게 다시 시작하면 된다.

http://www.sfsu.edu/~helpdesk/ssh/ssh_osx/ssh_osx.htm 에 아래 내용이 잘 나와있다.

1. Open Terminal in the Applications > Utilities folder.
   
2. Type open   .ssh in the terminal window then press the Return key.  This opens the .ssh folder which contains the file known_hosts.
   .
3. Drag known_hosts into the trash then close the .ssh folder.

Deleting know_hosts removes all host keys from your computer so all hosts will be treated as though you are connecting to them for the first time.