How to establish ssh key pair when "Host key verification failed"

I have set up ssh key pairs between my desktop and two servers, and from the servers to my desktop, but after reinstalling the OS on my desktop, I can't re-establish the key-pair going into my desktop by this: ```shell mkdir ~/.ssh chmod 700 ~/.ssh ssh-keygen -t ssh-copy-id username@server ``` I get the following error: (names in *italics* changed to protect the innocent My desktop is Ubuntu, and I can't find the answer [ here][1]) > @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ > @ 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 > *ab:cd:ef:gh* > Please contact your system administrator. > Add correct host key in /home/*user*/.ssh/known_hosts to get > rid of this message. > Offending key in /home/*user*/.ssh/known_hosts:1 > RSA host key for *user.server* has changed and you have requested strict > checking. > Host key verification failed. [1]: https://help.ubuntu.com/community/SSH/OpenSSH/Keys