Enable root user password to login EC2 on Ubuntu

Edit your SSHd config to allow password based logins:

    sudo nano -w /etc/ssh/sshd_config

Add the following line to /etc/ssh/sshd_config:

    PasswordAuthentication yes

Copy your authorized SSH keys if you want to log in via keys as well:

    sudo mkdir /root/.ssh

    sudo cp /home/ubuntu/.ssh/authorized_keys /root/.ssh/

Reload your SSHd config:

    sudo reload ssh

Now you can login as root!