Here is a short ssh command, if you need to login to a host but the keys changed there (e.g. logging into a machine that runs a live image to rescue stuff):
ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o LogLevel=ERROR user@host
You could remove the
LogLevel Option, it will only supress the warning in the beginning, that the host was added to the known_hosts.