How to fix warning about ECDSA host key

Question

I'm trying to setup passwordless ssh on an Ubuntu server with ssh-copy-id myuser@myserver, but I'm getting the error:

Warning: the ECDSA host key for 'myserver' differs from the key for the IP address '192.168.1.123'

What's causing this, and how do I fix it? I tried deleting the .ssh directory on the remote machine, and running ssh-keygen -R "myserver" locally, but this doesn't resolve the error.

Answer 1

Remove the cached key for 192.168.1.123 on the local machine:

ssh-keygen -R 192.168.1.123

Answer 2

(OK, to Mark0978 point, I have edited this to try to better answer the question)

Question: What's causing this, ... ?

So the ssh server host key changed. What caused the change? It is hard to say. Here are some guesses:

• Did sshd on myserver start using ECDSA keys, so it is a new key type?
• Was myserver recently re-installed?
• Was sshd on myserver recently re-insalled so a new ssh host key was generated?
• Did someone re-generate or replace the sshd host key?
• Has the IP address of myserver changed so that a different host is answering to that IP address?

Question: ... and how do I fix it?

As others have already answered, remove the cached ECDSA host key for myserver that your account has cached.

Answer 3

This thread may help:

http://www.linuxquestions.org/questions/linux-security-4/ssh-ecdsa-rsa-conflict-872520/

Essentially, you want to remove both the RSA and ECDSA keys for that host, then use ssh-keyscan to put them back into your known_hosts file in a way that won't cause this conflict. It worked for me when I had the same issue.