[vtkusers] VTK MPI with SSH Display problem

[John Shalf]

Actually they can watch your keystrokes anyways (xhost or
not).  Unless you use ssh to encrypt your X11 connection,
all network traffic is in clear-text.

Unfortunately X11 doesn't forward GLX; it only forwards X11
traffic.  So ssh will fail to work properly if your graphics
uses GLX (the remote GL protocol extension to X) which would
force you to resort to the dubious "setenv DISPLAY
<host>:0;xhost+<host>" method.

-john

Robert Belleman wrote:
> 
> People,
> 
> DON'T use "xhost + host" to allow other machines to open X connections
> to your machine. Doing so will allow ANY user on that host (or any user
> ON ANY HOST ON THE INTERNET if you are foolish enough to just use
> "xhost +") to open a X connection to your machine. Others will then be
> able to catch any X event that is generated on your machine,
> INCLUDING KEYSTROKES.
> 
> This is a common way to catch passwords typed in by you when you remote
> login to another machine.
> 
> Instead, do one of the following:
> 
>   - SSH automatically forwards X connections on a secure channel, so use
>     ssh to start processes on other hosts (such as PVM/MPI processes).
>     If this doesn't work for some reason:
> 
>     - check that your DISPLAY variable is not overriden by your startup
>       files (.cshrc, .bashrc, etc.), SSH will do this automatically.
>     - you may have to pass the "-n" flag on the commandline to ssh
>       commands,
>     - you may have to add "ForwardX11 yes" to "$HOME/.ssh/config",
>     - check that "xauth" is installed on the remote machine; if it isn't
>       installed on a "known" location (like "/usr/X11R6/bin/xauth"),
>       set "XAuthLocation" in "$HOME/.ssh/config",
>     - have your sysadmin check the SSH settings and the settings of
>       network devices between you and the remote host,
> 
>   - Look into xauth(1),
> 
>   - Your Vtk program may not even need an X connection if the only thing
>     you want to do is preprocessing on another host. If this is true,
>     then don't create any structures that initiate X connection (i.e.
>     do "wm withdraw ." from tcl scripts, or don't create RenderWindows).
> 
> -- Rob
> 
> --
> [] Robert Belleman         X  Section Computational Science            []
> [] robbel at science.uva.nl  |X| University of Amsterdam, the Netherlands []
> [] tel: (+31) 20 525 7510  X  http://www.science.uva.nl/~robbel/       []
> 
> On Wed, Jul 18, 2001 at 10:17:38AM -0500, Juerg Tschirren wrote:
> >
> > I never used the MPI option with VTK, but I do run VTK on a remote machine
> > through an SSH connection. It looks like you didn't do one or both of the
> > following two steps:
> >
> >   If your application runs on machine A and wants to display something on
> > machine B, then you have to:
> >
> >   1. on machine A type
> >
> >      export DISPLAY=B:0.0
> >
> >      assuming you are using the Bash shell. B has to be the valid
> >      network name of machine B, or its IP address.
> >
> >   2. on machine B type
> >
> >      xhost + A
> >
> >      in order to allow machine A to do an X connection to B. Again, A
> >      hast to be a valid network name (resolvable by DNS) or an IP address.
> >
> > Hope that helps
> >
> > Juerg
> >
> >
> > On Wed, 18 Jul 2001, Simon Winberg wrote:
> >
> > > Hi all,
> > >
> > > I've got VTK compiled with the MPI option, and am testing the
> > > ParallelIso program. I'm using ssh with the ssh-agent to connect to the
> > > other PC's.
> > >
> > > When I execute the program (using the lamexec command) the
> > > application runs for a few seconds and then crashes (see output
> > > below). I can run the application fine on one PC simulating multiple
> > > processors, but when I add any of the other PCs in my cluster I get this
> > > error:
> > >
> > > --------
> > > $ lamexec -np 3 ParallelIso
> > >
> > > Update 3000 took 0.531551 seconds to produce 68 triangles
> > > Update 1750 took 0.828511 seconds to produce 88310 triangles
> > > Update 500 took 0.738054 seconds to produce 64982 triangles
> > > Update 3000 took 2.94585 seconds to produce 68 triangles
> > > ERROR: In vtkXRenderWindow.cxx, line 176
> > > vtkMesaRenderWindow (0x8235550): bad X server connection.
> > >
> > > ERROR: In vtkMesaRenderWindow.cxx, line 122
> > > vtkMesaRenderWindow (0x8235550): bad X server connection.
> > > --------
> > >
> > > I have tried the other example programs with similar results.
> > > Could this be a problem with how ssh handles exporting of the display?
> > >
> > > Any ideas?
> 
> _______________________________________________
> This is the private VTK discussion list.
> Please keep messages on-topic. Check the FAQ at: <http://public.kitware.com/cgi-bin/vtkfaq>
> Follow this link to subscribe/unsubscribe:
> http://public.kitware.com/mailman/listinfo/vtkusers