VNC

There seem to be a lot of VNC viewers out there, which ones do you recommend?

TurboVNC and TigerVNC are good choices and the ones we recommend. Of these two, TigerVNC has a nicer GUI and appears to have slightly better performance. In principal any viewer supporting the VNC protocol can be used, but the two mentioned are well maintained and provide good performance. 

TightVNC and RealVNC might also work, but sometimes seems to have noticeable lower performance (especially on Windows). Plus, we have seen issues with the TightVNC client not supporting the required authentication methods we use on the server side.

Note that "Screen Sharing" on MacOS is not usable as a VNC viewer, at least, not in our tests. Use the TurboVNC viewer package instead.

The VNC server used on Snellius and Lisa is actually TurboVNC.

The desktop resolution is quite low in the VNC session, can I change it?

Yes, use the -r <w>x<h> option with vnc_desktop. Another option is to set the environment variable VNC_DESKTOP_RESOLUTION in your shell's startup script, again to <w>x<h>, so you don't have to use -r each time.

How do I run the VNC job within a SLURM reservation?

$ vnc_desktop <options> -- --reservation=<reservation-name> 

Something strange is going on with my VNC session, is there a VNC server log file I can check?

Yes, check the files in the .vnc directory in your home directory. E.g., for a VNC server running on gcn10:1 check gcn10.1.log.

After switching between my VNC viewer and some other application on my local machine the VNC viewer seems to get confused about the keys I press

Some VNC viewers (and versions) have problems when you're using Alt-TAB to switch to and from the viewer application. This is probably because the Alt keypress event is captured by the VNC viewer, but the subsequent TAB keypress will take away keyboard focus and so the viewer application never receives a release event for the Alt key, thinking it is still pressed when you switch back to it.

When you find that the Alt-key seems to be "stuck" in your VNC viewer simply press and release Alt. This usually fixes it.

Isn't it possible that somebody other than me snoops on my VNC session?

In theory, somebody also logged into Snellius could try to connect to the VNC server you started on a render node. But:

1. Data sent between the remote VNC desktop on Snellius and the client running locally is encrypted using an SSH tunnel
2. For being able to log into Snellius they need to have their IP address whitelisted and have valid login credentials
3. They need to know your VNC password (and you have picked a strong enough passphrase that can't be guessed, right?)

All in all, the risks should be minimal.

Is it possible to share my VNC session with others so that we can discuss the visualization output while not being in the same place?

No, the current security setup does not allow users to share VNC passwords, as they are the same as your CUA password.

VirtualGL

Is there a way to get statistics on rendering performance?

More or less. You can use the +pr option when starting your OpenGL application with vglrun, e.g. vglrun +pr paraview. This will periodically produce statistics in the terminal window on

• Readback - the speed with which the rendered output is read-back from the video card
• Blit - the speed at which the captured images are integrated in the VNC session
• Total - the total speed for the above steps, including overhead

The actual image compression (before network transmission to the VNC client) is performed by the VNC server. There's currently no easy way to get statistics on the compression performance.

Is there more documentation on VirtualGL?

Yes, see http://www.virtualgl.org/About/Introduction and http://www.virtualgl.org/About/Background

Is it possible to use VirtualGL's Image Transport method?

Not at the moment. We only provide remote rendering using VNC, but VGL Image Transport might be added in the future.