This article applies to NoMachine client v. 4 or 5, the 'NoMachine login' authentication method is no longer supported since v. 6, please read also https://www.nomachine.com/AR11O00947

NoMachine client 4 or 5 uses by default the NX protocol, which is not supported by NX servers earlier than version 4.

When connecting to NX 3.5.0 servers, remember that older servers support only SSH connections and the 'NoMachine login'. You will therefore be able to connect to your 3.5.0 server only using the SSH protocol set in the connection GUI.

To change the protocol to SSH:

Step 1 - Double click on the connection in the NoMachine client GUI.

Step 2 - From the successive panel, click on Edit.

Step 3 -  Choose to use SSH protocol. Note that the default is NX, not supported by the server 3.

Step 4 - Click on Advanced.

Step 5 - Choose 'Use the NoMachine login'. Note that the default is 'Use the system login', not supported by the server 3.

Step 6 - Click Continue to finish the set-up procedure

Step 7 - Connect to start the session.
 

Note that since version 4 most of the session configurations that in the 3 happened BEFORE starting the session, now happens at RUN TIME, based on information provided by the server after the connection has taken place. This includes the type of session (shadowing of the physical screen or creation of a new virtual desktop), the X client or desktop environment (GNOME, KDE, custom session, etc.), the display resolution, the configured printers, etc.

Compared to server version 3, server 4 lets you can change most settings while the session is already running (keyboard and input settings, display resolution, display quality, compression settings, configured printers and forwarded devices). To change the display resolution, a setting that users of the 3 versions were accustomed to specify before connecting, you will normally operate on the control panel of the desktop of choice. When connecting to a virtual desktop you can change the resolution to any possible setting, since virtual desktop sessions are not subject to the limitations of your video driver or monitor. When connecting to a physical desktop you will have to choose among the resolutions listed by the X.org server for the display. Depending on the driver or monitor, these may not match the resolutions supported by the client. These resolutions are listed by X.org based on the resolutions advertised by the driver or monitor. There is nothing NoMachine can do to change them. As an additional functionality, since version 4.1 the client 4.1 offers the option of automatically adapting the display resolution of the server to the resolution of the client while connected. This function is not available in the client 4.0.