== Graphical Login (VNC) ... details
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VNC follows a very general approach, where a remote graphical desktop on one node of the remote cluster is started. \\
On the user's workstation only a lightweight VNC viewer has to be installed. \\
The graphical screen of the remote desktop is send as an image from the cluster to the viewer on the fly.

The user can work with this remote graphical desktop in the usual way, just by interacting with keyboard and mouse. \\
This is a very convenient way to work on a remote machine, not only for data visualization.

VNC offers the ability to detach from a session (running in a VNC server) and then attach back at a later time. \\
That means, that the user can close the VNC viewer on his/her computer and any application started in the VNC session on the server keeps on running - they do not pause or even be killed. \\
Later on the user can connect back to the same VNC session (even from a different computer) and keep on working. \\

[[Image(Trac_Setup_VNC.png, 380px)]]\\

==== hardware accelerated rendering (OpenGL) 
[[Image(https://upload.wikimedia.org/wikipedia/commons/thumb/6/67/X11transport.png/600px-X11transport.png, 200px, align=right, margin=0)]]
Whenever an OpenGL capable visualization software, like !VisIt, is started on the remote cluster node, \\
OpenGL commands can be redirected to the GPU of this node with the help of [http://www.virtualgl.org VirtualGL]. \\
* ... using '''vglrun''' (e.g. vglrun paraview)
This way the hardware accelerated rendering capabilities of a cluster node (if available) can be exploit for remote rendering. \\
(attention: __without__ VirtualGL software, rendering using the CPU instead of the GPU must be used (if available), which is much slower).


==== e.g. ParaView
Open a terminal in your VNC session and:
{{{ #!sh
# What versions of ParaView are available?
module spider ParaView

# load ParaView dependency
module load intel-para

# load ParaView
module load ParaView
}}}

{{{ #!sh
# start ParaView Server and GUI using VirtualGL for hardware acceleration
srun -n 24 vglrun pvserver
vglrun paraview
}}}
Connect to the pvservers on localhost:11111

==== e.g. !VisIt
Open a terminal in your VNC session and:
{{{ #!sh
# change Stage
module use /usr/local/software/jureca/OtherStages
module load Stages/.Stage1

# What versions of VisIt are available?
module spider VisIt

# load VisIt dependency
module load intel-para/2015.07

# load VisIt
module load VisIt/2.10.0
}}}

{{{ #!sh
# start VisIt using VirtualGL for hardware acceleration
vglrun visit -hw-accel
}}}


== Hints

* press F8 to enter VNC-Viewer Options (example: toggle to full screen)

* sync clipboard between client and server
{{{ #!ShellExample
    vncconfig -poll=100
}}}

* To reset your VNC-password delete ~/.vnc/passwd

----
any feedback welcomed - [mailto:h.zilken@fz.juelich.de], [mailto:j.goebbert@fz-juelich.de]