To access RetroPie via SSH using root account:

• Open file sshd_config located in etc/ssh:
  sudo nano /etc/ssh/sshd_config 
  • Find line:
    PermitRootLogin without-password
  • Comment it out (or delete) it and replace with:
    PermitRootLogin yes
  • Save changes (CTRL + X)
• Set root password:
  sudo passwd root
• Reboot your Raspberry Pi

June 2017
Raspberry Pi 3 Model B
RetroPi 4.2