theunholy@ubuntu:~$ sudo ssh localhost
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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 a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
3d:c6:13:19:8b:2e:de:9e:3b:cf:47:6b:f6:c6:f1:dc.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /root/.ssh/known_hosts:1
  remove with: ssh-keygen -f "/root/.ssh/known_hosts" -R localhost
ECDSA host key for localhost has changed and you have requested strict checking.
Host key verification failed.
theunholy@ubuntu:~$ sudo rm /root/.ssh/known_hosts && rm ~/.ssh/known_hosts
theunholy@ubuntu:~$ sudo ssh localhost
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is 3d:c6:13:19:8b:2e:de:9e:3b:cf:47:6b:f6:c6:f1:dc.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
root@localhost's password:
Permission denied, please try again.
root@localhost's password: