NoMachine NX remote Linux desktops

Setting up and using the NX Client

The best system for using a graphical Linux desktop environment on a remote computer is NX, which is similar to VNC. Unlike VNC, the NX server takes care of session management, and performance is usally better than VNC over a low bandwidth connection. The main NX server at ESSC is called saturn, and there is also a backup server called jupiter. Windows, Mac, Linux and Solaris versions of the NX Client are available from NoMachine. This How-To in the CentOS wiki has a section covering NX client configuration which applies to all platforms. Follow these instructions to connect to saturn, but instead of UNIX/GNOME use UNIX/KDE as the desktop type. KDE is recommended for saturn because of problems caused by an NX bug that some GNOME users have experienced. Further details can be found under "Mouse and keyboard input problems for GNOME users on saturn" below.

Saturn and jupiter both use the default DSA key provided with the NX client, so there is no need to open the key management window during the client setup process. To connect to jupiter there are minor differences to the procedure outlined in the CentOS wiki, mainly because the GNOME and KDE desktop environments have been disabled for performance reasons. The much lighter XFCE4 desktop environment should be used instead, which will enable more users to share the same desktop server before poor performance becomes and issue. To set up the NX client for XFCE4, select "Custom" instead of "GNOME" or "KDE" from the pull down list of server types in the NX Connection Wizard, or the "General" tab in the configuration window of the NX Client. Press the "Settings" button, and in the window that appears select "Run the following command". Enter the command "nxwrapper startxfce4" in the text box, and then select the option "New virtual desktop" at the bottom. In the "Advanced" tab of the configuration window, disable (i.e. un-tick) the option that says "Disable encryption of all traffic", which may or may not be set by default. In theory it should be possible to run without encryption via VPN, but in practice this mode does not seem to work with the FreeNX server.

One thing to watch out for with NX is changes in colour depth (sometimes called "colour quality") between different remote computers. If you start a session on a computer with the display set to a colour depth of 24 or 32 (i.e. 24 bits or 32 bits) you will not be able to resume that session on a computer with a display colour depth of 16 or below. Most modern computers use 24 or 32-bit colour, so this restriction rarely causes a problem.

When you have finished working you can suspend your remote desktop session instead of logging out, simply by closing the NX desktop window on you host computer's desktop (e.g. your thin client or Windows PC). NX will ask you if you want to "Disconnect" or "Terminate" the session. Choose "Disconnect" in order to suspend the session. This will enable you to resume the session later, possibly on another client computer in another location, where you will find all your applications and network connections still running as you left them. If you have a Windows PC or laptop you can use your Linux desktop session on saturn or jupiter at the same time as Windows applications such as Microsoft Office. You can copy and paste between Windows applications and Linux applications running on saturn or jupiter.

LibreOffice replaces OpenOffice on jupiter

The OpenOffice .org project has been suspended following Oracle's decision to discontinue development and donate the source code to the Apache foundation in June 2011. OpenOffice is now an Apache Incubator Project and the code migration process is still going on at the time of writing (January 2012). In the meantime, a fork of OpenOffice called LibreOffice has continued where OpenOffice left off, and most Linux distributions now use this as the standard office suite instead of OpenOffice .

LibreOffice has replaced OpenOffice on jupiter, which means that file associations for OpenDocument and Microsoft Office formats in applications such as Firefox, Thunderbird and Thunar (the XFCE4 file manager) might not all work. However, it is easy to reconfigure your applications to use LibreOffice to open Microsoft and OpenDocument format documents. Here are some brief instructions for common applications.

• Thunar (file manager). Right click on the document you wish to open. If it doesn't say "Open With LibreOffice ..." select "Open with other application" and then choose the appropriate LibreOffice application from the list.
• Firefox and Thunderbird. When you try to open an email attachment or a document specified by a URL a window appears with two options: "Open with" and "Save as". If the application specified for the "Open with" option is not LibreOffice , choose "Other..." from the pull-down list. In the window that appears put "libreoffice3.4" in the Location bar.

Mouse and keyboard input problems for GNOME users on saturn

At the time of writing (20th October 2011) some users have been experiencing occasional problems caused a bug in the NX server software, which causes NX sessions to stop responding to mouse and/or keyboard input. Until the bug is fixed the recommended work-around is to use KDE instead of GNOME. To start a new KDE desktop session in NX, click on the "Configure" button in the bottom left of the NX Client login window, and then selecting "KDE" from the pull-down list under "Desktop". If your GNOME session is still running you will be given the option of terminating that session or starting a new one. Please terminate the GNOME session if you possibly can in order to free up resources for other users.

It is possible to repair a GNOME desktop session after the fault has occurred. The first thing to do is find out if you still have keyboard input by trying to close the NX window on the host computer's desktop. When the "Disconnect, terminate or cancel" window appears press the tab key a few times. If the highlighted button changes when you do this, press Tab again until "Cancel" is highlighted and press Enter. Then follow the instructions below.

1. Press ALT-F2 to bring up the "Run Application" window.
2. Enter the command "xterm" and press Enter.
3. In the terminal window that appears enter the command "DISPLAY=$DISPLAY metacity --replace $" in a bash shell. If your default shell is not bash enter the command "bash" to start a new bash shell first.

If you don't have mouse or keyboard input, login to saturn from another computer (e.g. jupiter), and then enter the command "ps ux | grep nxagent". Look for the display number of your NX session, which is :1171 in the example below.

54 resc@saturn>ps ux | grep nxagent
resc    23085 0.3 0.3 41332 26532 ?       S   18:18  0:01 /usr/NX/bin/nxagent -D -options /users/resc/.nx/C-saturn-1171-0C6CA84C65CF8F31DD615F1BAA411719/options -name NX - resc@saturn:1171 - saturn :1171
resc    25449 0.0 0.0  2808  724 pts/56  R+  18:25  0:00 grep nxagent

When you have found the display number, start a bash shell (if your default shell is not bash) and enter a command like the following to enable mouse and keyboard input to your stuck GNOME session.

55 resc@saturn>bash
resc@saturn:~>DISPLAY=:1171 metacity --replace &
[1] 25502
resc@saturn:> exit
exit

Menu related problems with KDE on saturn

There is a very occasional problem with KDE on saturn, where some menu items such as "Firefox" and "terminal" become ineffective. This happens very rarely, but if ever happens o you, your KDE settings can easily be returned to standard by entering the following command.

cp -rf /nerc/scripts/newuser/.kde/share/config ~/.kde/share/

You may have to log out and log in again to activate the changes.

-- DanBretherton - 08 Dec 2011