University of Pretoria
Operational / Internal Site

Pass-though NX Configuration

In order to allow limited graphical access from off-campus, the pass-though servers provide a facility based on NX_technology. NX compresses the X11 data to minimize the amount of data transmitted. NX also makes extensive use of caching to make the session as responsive as possible.


In order to use this facility, the following are necessary:

  1. An active EECE Kerberos / AFS account
  2. A suitable NX client for the off-campus computer that will be used to connect
  3. Import of the correct security keys for the pass-through servers

By default a NX installation uses a default set of keys and this introduces a slight security risk. The EECE pass-through servers therefore make use of individual custom keys for each server. You must therefore import the server specific keys before attempting to make a NX connection to the pass-though servers. Failure to do so will result in a lockout of your system. Use the table of contents on the right to skip the client installation procedure if you already have the necessary client installed.


To be clear, when making a NX connection to the pass-through servers, you are logging into the pass-through servers. If you wish to run graphical programs on, for example the clusters, you will need to open a terminal window (there is an icon on the bottom bar or right-click on the background) and SSH to the desired node with X11 forwarding enabled. Example:

  ssh -Y alpha2-1

Once connected to the desired cluster node, you start the application as normal. Graphical output will now be transfered to the pass-through by means of the standard X11 protocol. From there it will be transfered by the compressed NX protocol to your client machine.

Note that the UP firewall at times drops active connections. It is not clear why this happens and this effect started occurring after a recent firewall software update. It is therefore recommend that you not rely on long running sessions (although sessions have 3+ hours have been achieved).

Client Installation

Various NX clients exist, with the official client being the client from NoMachine. This discussion will focus on the official Windows clients only, which are available for most platforms. For other platforms it is assumed the user is able to perform the installation without detailed instructions. The clients can be downloaded from the NoMachine site. Local versions for are available on the department archive (for Windows and Mac). The Linux (Debian) versions are part of the EECE Debian repository and can be installed directly using APT (named nxclient).

  • For Windows the client installation is required, as well as the installation of X11 fonts. When the main installer is executed, a welcome screen will appear. Click on Next to continue the installation.

NX Setup Wizard welcome window

  • The next window allows the installation directory to be configured. Click on Next to accept the default location.

Select Destination Location window

  • The next window gives the option to configure the start menu where the NX applications are registered. Clink on Next to accept the default.

Start menu folder configuration

  • In the next window you have the option of allowing a desktop icon to be installed. Select as appropriate and clink on Next to continue.

Select additional tasks window

  • The next window provides a summary of the installation configuration. Click on Install in the next window to begin the installation.

Ready to install window

  • The final window will indicate that the installation was successful, click on Finish to close the installer.

Installation complete window

Installation of fonts

In order to support the fonts used on the X11 system, the Windows client requires the installation of X11 fonts. Begin by installing the “75dpi” fonts, followed by the “100dpi”, “misc” and “other” fonts. The procedure is similar to that for the client, just use all the default selections and simply click on Next, Install or Finish as appropriate.

Connection configuration and Custom Keys

The final step is to define a session configuration for each of the pass-through servers and import the custom keys. When the client is launched, a login window is display. Initially the “Session” field is empty as no sessions have been defined.

  • Create a new session by choosing an appropriate name (e.g. PST or WIENER) and clicking on Configure.


  • You will be asked if you wish to create a new session, do so.


  • You will now be presented with a session configuration dialog as shown below. Update the fields as shown for the PST server and click on Next to continue.


  • On the next window configure the type of login session as “Custom”. To lower the resource requirements on the pass-through servers, the only support session is the Lightweight X11 Desktop Environment (LXDE). Click on Settings to configure the session parameters and a new window will appear.


  • To start a LXDE session on the pass-through server, update the configuration as shown below. Click on Ok to close the window and return to the previous window. Note the command must be: exec startlxde


  • Click on Next to continue the configuration. On the next window you will be given an option to create a session link on your desktop. Select as appropriate and click on Next to continue.


  • At this point the session creation has been completed. The next step is to import the server specific custom keys. Using a SCP or SFTP client, download the custom client keys from each of the pass-through servers and save them somewhere you will be able to find them. The keys are located at /etc/nx_client.key on the pass-through server. Now again click on Configure.


  • Next click on Key below the server address. This opens a new window in which the key can be imported.


  • In the new window click on Import to import the key.


  • Browse to where you saved the key file and select the key file. Click on OK to complete the import. Click on Save and close the import window.


At this stage you should be able to establish a NX session to the pass-through by entering your EECE Kerberos / AFS username and password and clicking on Login.