Reply To: Unable to connect on Ubuntu Forum / NoMachine for Linux / Unable to connect on Ubuntu / Reply To: Unable to connect on Ubuntu March 24, 2014 at 14:48 #2777 rezaParticipant It seems that you cannot connect to your servers because of Firewall or NAT. If you are using NX protocol please ensure that the Security Group for your EC2 instance allows connections on port 4000. This reply was modified 9 years ago by reza.