Hi, I removed your link because it points to a tutorial about the old version 3.5.0, and these forums are dedicated to version 4 client to version 4 server. The tutorial will only confuse users. For headless Linux servers, your best bet is to look at our own article:
https://www.nomachine.com/AR10K00710
There have also been similar enquiries about NoMachine running on EC2 which you can consult here if you like, among them:
https://www.nomachine.com/forums/topic/unable-to-connect-on-ubuntu
https://www.nomachine.com/forums/topic/amazon-ec2-installation