x-window-system.md

X Window System 
===============

  

The X Window system is a principal way to get GUI access to the
clusters. The **X Window System** (commonly known as **X11**, based on
its current major version being 11, or shortened to simply **X**, and
sometimes informally **X-Windows**) is a computer software system and
network
[protocol](http://en.wikipedia.org/wiki/Protocol_%28computing%29 "Protocol (computing)")
that provides a basis for [graphical user
interfaces](http://en.wikipedia.org/wiki/Graphical_user_interface "Graphical user interface")
(GUIs) and rich input device capability for [networked
computers](http://en.wikipedia.org/wiki/Computer_network "Computer network").

The X display forwarding must be activated and the X server running on
client side

### X display

In order to display graphical user interface GUI of various software
tools, you need to enable the X display forwarding. On Linux and Mac,
log in using the -X option tho ssh client:

`
 local $ ssh -X username@cluster-name.it4i.cz
`

### X Display Forwarding on Windows

On Windows use the PuTTY client to enable X11 forwarding.   In PuTTY
menu, go to Connection->SSH->X11, mark the Enable X11 forwarding
checkbox before logging in. Then log in as usual.

To verify the forwarding, type

`
$ echo $DISPLAY
`

if you receive something like

`
localhost:10.0
`

then the X11 forwarding is enabled.

### X Server

In order to display graphical user interface GUI of various software
tools, you need running X server on your desktop computer. For Linux
users, no action is required as the X server is the default GUI
environment on most Linux distributions. Mac and Windows users need to
install and run the X server on their workstations.

### X Server on OS X

Mac OS users need to install [XQuartz
server](http://xquartz.macosforge.org/landing/).

### X Server on Windows

There are variety of X servers available for Windows environment. The
commercial Xwin32 is very stable and rich featured. The Cygwin
environment provides fully featured open-source XWin X server. For
simplicity, we recommend open-source X server by the [Xming
project](http://sourceforge.net/projects/xming/). For
stability and full features we recommend the
[XWin](http://x.cygwin.com/) X server by Cygwin

 |How to use Xwin |How to use Xming |
 | --- | --- |
 |[Install Cygwin](http://x.cygwin.com/)Find and execute XWin.exeto start the X server on Windows desktop computer.[If no able to forward X11 using PuTTY to CygwinX](x-window-system/cygwin-and-x11-forwarding.html)\ |<p>Use Xlaunch to configure the Xming.<p>Run Xmingto start the X server on Windows desktop computer.\ |

Read more on
[http://www.math.umn.edu/systems_guide/putty_xwin32.html](http://www.math.umn.edu/systems_guide/putty_xwin32.shtml)

### Running GUI Enabled Applications

Make sure that X forwarding is activated and the X server is running.

Then launch the application as usual. Use the & to run the application
in background.

`
$ module load intel (idb and gvim not installed yet)
$ gvim &
`

`
$ xterm
`

In this example, we activate the intel programing environment tools,
then start the graphical gvim editor.

### GUI Applications on Compute Nodes

Allocate the compute nodes using -X option on the qsub command

`
$ qsub -q qexp -l select=2:ncpus=24 -X -I
`

In this example, we allocate 2 nodes via qexp queue, interactively. We
request X11 forwarding with the -X option. It will be possible to run
the GUI enabled applications directly on the first compute node.

**Better performance** is obtained by logging on the allocated compute
node via ssh, using the -X option.

`
$ ssh -X r24u35n680
`

In this example, we log in on the r24u35n680 compute node, with the X11
forwarding enabled.

HTML commented section #1 (no GUI on Compute nodes - Xvfb)

### The Gnome GUI Environment

The Gnome 2.28 GUI environment is available on the clusters. We
recommend to use separate X server window for displaying the Gnome
environment.

### Gnome on Linux and OS X

To run the remote Gnome session in a window on Linux/OS X computer, you
need to install Xephyr. Ubuntu package is 
xserver-xephyr, on OS X it is part of
[XQuartz](http://xquartz.macosforge.org/landing/).
First, launch Xephyr on local machine:

`
local $ Xephyr -ac -screen 1024x768 -br -reset -terminate :1 &
`

This will open a new X window with size 1024x768 at DISPLAY :1. Next,
ssh to the cluster with DISPLAY environment variable set and launch
 gnome-session

    local $ DISPLAY=:1.0 ssh -XC yourname@cluster-name.it4i.cz -i ~/.ssh/path_to_your_key
    ... cluster-name MOTD...
    yourname@login1.cluster-namen.it4i.cz $ gnome-session &

On older systems where Xephyr is not available, you may also try Xnest
instead of Xephyr. Another option is to launch a new X server in a
separate console, via:

`
xinit /usr/bin/ssh -XT -i .ssh/path_to_your_key yourname@cluster-namen.it4i.cz gnome-session -- :1 vt12
`

However this method does not seem to work with recent Linux
distributions and you will need to manually source 
/etc/profile to properly set environment
variables for PBS.

### Gnome on Windows

Use Xlaunch to start the Xming server or run the XWin.exe. Select the
''One window" mode.

Log in to the cluster, using PuTTY. On the cluster, run the
gnome-session command.

`
$ gnome-session &
`

In this way, we run remote gnome session on the cluster, displaying it
in the local X server

Use System-&gt;Log Out to close the gnome-session