NoMachine is designed to work out-of-the-box on headless machines on all supported platforms. On Linux a desktop environment must be installed.

Nevertheless, in some cases users can experience bad rendering problems when connecting to the remote host. This happens when the GPU is not "fully functional", when the monitor is not attached and mainly depends on the GPU model and the graphic card drive. 

A common solution is to adopt a fake display dongle (also called 'dummy dongle') inserted in the video card port to simulate the presence of a screen and force the system to take full advantage of the GPU as if a real monitor is connected.

If the remote host is Linux there are other alternative solutions, please see https://kb.nomachine.com/AR03P00973.