== Graphical Login 
[[PageOutline]]



[[Image(https://upload.wikimedia.org/wikipedia/en/thumb/5/51/Virtual_Network_Computing_%28logo%29.svg/220px-Virtual_Network_Computing_%28logo%29.svg.png,100px, align=left, margin=0, link:vnc3d)]]
[[Image(xpra-logo.png, 100px, align=left, margin=0, link:vnc3d)]] \\
[[Image(virtualgl.gif, 200px, align=left, margin=10, link=wiki:vnc3d)]]

[[Image(screenshot_vnc.png, 400px, align=right, margin=10, link=wiki:vnc3d)]]

Remote visualization, either implemented within visualization applications themselves or through server software, eliminates the need for off-site file transfers and allows HPC users to run a broad range of visualization tools 
in-place on the supercomputer where the data resides and more compute resources are available.

Remote visualization provides a graphical access by \\
* transmitting the keyboard and mouse events from your computer to the remote machine.
* relaying the graphical screen updates back in the other direction.
* is application-independent (no need for remote visualization support inside the specific application).

A broad variety of Linux applications with graphical user interface and/or need for OpenGL can be used directly on the supercomputers via remote visualization.
Multiple software solutions for remote visualization are possible from which we recomment on our system VNC or Xpra.
Our decision is based on the mandatory requirement for support of
* server-side rendering with OpenGL (using VirtualGL)
* client-support on many operating systems (Linux, MaxOS, Windows, etc.)
* flexible use in user specific setups
* optimized even for low bandwidth connections

In general one can distinguish between '''full desktop mode''' and '''seamless window mode''' solutions.\\
While using a full desktop mode presents a complete desktop environment (on JUWELS we run XFCE) in a single window on the user´s workstation, \\
the seamless window mode makes applications running on JUWELS appear on the local desktop as normal windows managed by the local window manager.

The solution for remote visualization allowing a remote full desktop on frontend nodes and/or compute nodes is provided using '''Virtual Network Computing (VNC)'''.\\
For access to remote seamless windows we recomment '''X Persistent Remote Applications (Xpra)''' as a light-weight and performant solution.


=== How do I start VNC?
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[[Image(manual_icon.png, 60px, align=left, margin=0, link=wiki:vnc3d/manual)]]

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'''vncserver/ssh/vncviewer''' (manual connection for VNC)
  * manual start of VNC server on JUWELS
  * manual tunnel for VNC data
  * manual start of VNC viewer on local machine
...................................................................................................................................................................................\\
'''[wiki:vnc3d/manual ==> More instructions <==]'''
 }}}
}}}

\\
=== How do I start Xpra?
{{{#!table style="border:none; text-align:left; margin:0px"
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[[Image(xpra-logo.png, 60px, align=left, margin=0, link=wiki:vnc3d/xpra)]]

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[[Image(Xpra_GUI.png, 120px, align=right, margin=0, link=wiki:vnc3d/xpra)]]

'''Xpra''' (X Persistent Remote Applications)
  * provides a '''remote seamless window''' solution.
  * this is the best replacment for ssh -X
  * survives disconnect & reconnect
  * every window appears as a separate window on the user’s desktop
  * graphical window is encoded to a video stream and send to the user´s desktop
  * focus is on fixed frame rate and dynamic frame quality

...................................................................................................................................................................................\\
'''[wiki:vnc3d/xpra ==> Download & Install Instructions <==]'''
 }}}
}}}

\\


\\
== Comparison of possible Remote Visualization Solutions ==

||= General Features         =||= '''VNC+Strudel''' =||= '''Xpra''' =||= '''ssh -X''' =|| ||= '''NX''' =||= '''RDesktop''' =||
|| Stability                  ||     ++      ||     ++       ||       -        || ||     +      ||        ++        ||
|| Performance over slow link ||     +       ||     ++       ||       --       || ||     ++     ||        +         ||
|| Server-side rendering      ||  VirtualGL  ||  VirtualGL   ||       -        || || VirtualGL  ||        -         ||
|| Suspend & resume session   ||    YES      ||    YES       ||       -        || ||   YES      ||        YES       ||
|| Seamless mode              ||    -        ||    YES       ||       YES      || ||   YES      ||        YES       ||
|| Full Desktop mode          ||    YES      ||   (YES)      ||      (YES)     || ||   YES      ||        YES       ||
|| Session Sharing            ||    YES      ||    YES       ||       -        || ||   YES      ||        -         ||
|| No local X-server needed   ||    YES      ||    YES       ||       -        || ||   -        ||        YES       ||
|| Main Issues                ||software setup|| software setup ||slow, chatty protocol,\\no server-side rend.,\\client X-server req.|| || -not avail.- || -not avail.-           ||
taken from https://winswitch.org/documentation/protocols/choose.html

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