X-Windows
Aka X11
1. |
What It Is |
- X11 is a platform-independent, networked-graphics framework.
2. |
What Does It Do? |
- Allows the graphical output of a program running on one machine to appear on a different machine.
- For example, the user-interface of a programme running on a central HPC
machine can be displayed on a user's local desktop (or laptop) by use
of X-Windows,
- e.g., the GUI of a programme submitted to SGE via "qrsh".
- N.B. The systems on which the programme is running and is displayed, to not need to be running the same OS or be of the same architecture.
3. |
Old School Example |
We can make clear how X-Windows works an old-school — pre-SSH tunnelling — example. To emphasise, this method of using X-Windows has been superceded; it is included here only to make explicit how X-Windows works.
We assume the remote system is man2e.nw-grid.ac.uk and that the local desktop is doolittle.rcs.manchester.ac.uk. On the local desktop, assuming you have an X-server running, then
desktop> xhost +man2e.nw-grid.ac.uk
# ...give permission for Man2e's X-server to talk to your desktop X-server...
i.e., give permission for Man2e's X-server to talk to your desktop
X-server. On the remote machine,
man2e> xclock -display doolittle.rcs.manchester.ac.uk:0This tells Man2e to display the programme — a simple clock — on your local desktop.
In practice, with this old-school method, there are additional hurdles to overcome. Is your local X-server configured to accept remote connections? Will the firewalls on both the remote system and your local system permit required connections? For these reasons, and also for better security, X-Windows is almost always tunnelled through an SSH connection — meaning that:
- the xhost command is not required;
- the display argument is not required;
- your local X-server will not have to be reconfigured;
- and there are no firewall issues.
4. |
Tunnelling X11 through SSH |
This is simpler than it may sound!
Let us repeat the above example, but using SSH tunnelling. On your local system, you have only to ensure that you have an X-server running. Then
desktop> ssh -X username@man2e.nw-grid.ac.uk
# ...note the "-X" (uppercase X)...
then on the remote system, simply type
man2e> xclock
# ..."-display ... ..." is not required...
That's it — the clock appears on your local desktop.
Using Compression
desktop> ssh -X -C username@man2e.nw-grid.ac.uk
5. |
With a Linux Desktop |
All common distributions of Linux (including RedHat/Fedora, SuSE and Ubuntu) start an X-Windows-based desktop (e.g., KDE or GNOME), i.e., an X-server is started by default.
6. |
With an OS-X Desktop |
OS-X comes with an implementation of X11 ready-installed. Simply start this to enable the functionality described above.
7. |
With a Microsoft Desktop |
Microsoft Windows does not come with an implementation of X-Windows, but MS-ready implementations are readily available and some are listed below. We also provide links to some tutorials describing how to use SSH-tunnelling with X-Windows with Microsoft Windows.
7.1. |
X-Servers for MS Windows |
- Xming — from the Web site: "is the leading free unlimited X Window Server for Microsoft Windows (XP/2003/Vista). It is fully featured, small and fast, simple to install. . ."
- Cygwin-X11 is a free X-Server for Microsoft Windows. It is part of Cygwin, a Linux-like environment for Microsoft Windows.
- Hummingbird eXceed, a commercial package, for which the University of Manchester has a site licence. The software can be downloaded from the IT Services applications Web site.
7.2. |
Running X-Windows Apps on MS Windows |