On ssh to root@ instruct user to try ubuntu@ instead

The official Ubuntu beta2 AMI will prevent ssh to root@ and allow ssh to ubuntu@ so that the image follows the normal Ubuntu standards for security (allowing user "ubuntu" to sudo).

Existing EC2 users are familiar with ssh to root@ given that most existing AMIs allow this, the EC2 documentation describes this, and tools like Elasticfox and the EC2 console provide commands to that effect. Given this, we need to help point users in the right direction when they try to ssh to root@ and the best approach (right message at the right time) seems to be to output a message when the user connects with ssh to root incorrectly.

The following steps are one way to accomplish this message while only showing it to somebody who has the correct key and not increasing security risks of letting users get in as root.

At first boot, when /home/ubuntu/.ssh/authorized_keys created, also create /root/.ssh/authorized_keys file. It would have the same content (keypair) with the additional first field like:

command="echo;echo 'Please ssh to the \"ubuntu\" user on this host instead of \"root\"';echo"

So, the entire /root/.ssh/authorized_keys file would end up looking something like:

command="echo;echo 'Please ssh to the \"ubuntu\" user on this host instead of \"root\"';echo" ssh-rsa AAAAB3N[...] KEYPAIRNAME

This results in an ssh attempt that looks like:

user@localhost:~$ ssh -i KEYPAIR.pem <email address hidden>

Please ssh to the "ubuntu" user on this host instead of "root"

Connection to ec2-174-129-189-221.compute-1.amazonaws.com closed.
user@localhost:~$