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Using OpenNX with the NX service

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This page explains how to install and configure OpenNX software on your computer so that you can use the Informatics NX service. We recommend that you try the NoMachine client instead in most cases because OpenNX is not being maintained or developed - there have been no new software releases for several years.

Some tips:

OpenNX Client Installation

First download the client software for your device. The OpenNX website provides packages and download/install instructions for OS X, Windows, and a variety of Linux distributions. The illustrations below are of OpenNX being configured on a Mac.


After OpenNX has been installed it will need to be configured. The first step is to start the OpenNX Connection Wizard.

If you are installing on a Mac, and it does not have an X11 app installed, you will be prompted to install one:

Following this prompt on a recent Mac will open a web page which gives an opportunity to download XQuartz, the open source replacement for Apple's X11 app. Download and install XQuartz if prompted to do so, then follow its advice to logout and log back in afterwards. Having done that, start Connection Wizard once more.

Configuring the Client

Here is a step-by-step guide to the required settings for the OpenNX client:

Step 1: Start the Connection Wizard

Step 2: Host Information

Choose which host you would like to use: for all users or for staff, research postgraduates and visitors.

Give the session a meaningful name. This can be anything you like, for example Informatics or Staff NX. The name can be particularly useful for those who use more than one NX server. The host must be set to either or The port number must be 22. The type of your internet connection can normally be left at the default of ADSL. If you know for certain that you have a much better (or much worse) connection then tweaking this option might improve your experience. You can alter the speed setting later if you want to experiment to find the best setting.

Step 3: Desktop Configuration

Select your preferred desktop environment. The default on DICE is GNOME, so that will be the most familiar option for many people. However the combination of GNOME and NX has caused problems for a number of users in Informatics. If your NX session behaves strangely and unpredictably then try setting your preferred desktop environment to another option such as KDE. We recommend a size setting of 1024x768 as that is likely to be suitable in most situations. You can alter these settings later if you decide you want to change anything.

Step 4: Encryption

The next step is to enable SSL encryption. We recommend that you enable encryption.

Step 5: Finishing Up

The configuration is now almost completed. The final step requires selecting the "Show the Advanced Configuration dialog" option prior to pressing the Finish button:

Step 6: Key Configuration

We use a locally-generated private key for the initial SSH connection. Both NX servers use the same key. You need to download the nxclient keyfile to a file (you may need to use "Save Link As..." in the File menu) so that it can be imported into your client configuration. Please note that this is a private key which must not be shared with others.

If you get a certificate security warning when trying to download the keyfile, it may be because your web browser does not trust the University's Certification Authority certificate. If this happens, install the University CA certificate in your browser then try again.

Once you have saved a copy of the key file, press the Key... button in the Server section of the Advanced Configuration dialog:

You will be presented with a Key Management dialog. Press the Import button.

This will present you with a file-chooser dialog which you can use to find the key file you previously downloaded.

Select the correct file and press the OK button. That will take you back to the Key Management dialog where you should press the Save button to store the new key.

This then takes you back to the main configuration menu where you finally need to press the top-level Save button. To complete the configuration stage and go to the login dialog press the OK button.

Once the key file has been imported it is no longer required and you must delete it. We may occasionally replace the key, in which case all users will be notified of the need to update their key.


Start the OpenNX app, from the same folder as the Connection Wizard. You will see a window like this:

Enter your DICE username and password and select the session (e.g. Informatics) that you previously configured.

The first time you access the service a message like this will appear during the authentication stage:

Please verify the details before pressing the Yes button - the NX page has the necessary details.

Any differences in the details are indicative of a potential security breach. In that situation you must not connect to the service, and you should immediately contact the Support Team to inform them of the issue.

We will occasionally need to move the service to a new machine, in which case all users will be notified of any changes to the host, address or fingerprint details.

The page NX sessions explains how to logout, and how to deal with suspended sessions.

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