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

As always, understand what changed.

Did the two hosts start using ECDSA keys, so it is a new key type? or did the host key change? Why? Was openssh-server upgraded and the key re-generated or a new ECDSA key generated?

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.