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# Running ParaView with MPI

## Introduction

If compiled with MPI support, ParaView can be launched like any other MPI application. The method for starting an MPI application is system and implementation dependent. Contact your system administrator for information on how this can be done. Once started, the user interface with appear on the display attached to the root process (process with id 0). On the displays attached to the other processes (satellite processes), independent render windows will appear. These do not have associated user interfaces and can not be manipulated by the user. Note that all processes must have access to a display. This does not require the presence of a monitor. As long as ParaView can open windows from all processes and read their contents, it will function properly. If multiple processes share the same display, it is very likely that windows opened by these processes will overlap. If this happens, the contents of those windows can not be read by ParaView and the image on the main window (the one with the user interface) will be corrupt. The same can happen if there are other windows which hide part or all of a satellite process' window. In the next release, ParaView will support off-screen windows to solve some of these problems.

## Unix/Linux Related Issues

The environment(s) in which ALL processes run must define the DISPLAY variable. Furthermore, they must have the right access to these displays. With some MPI implementations, it is possible to pass environmental variables to MPI processes. However, unless the DISPLAY variable is :0 or localhost:0, all windows will appear on the same display and ParaView will not function properly. Some MPI implementation use ssh which sets up X tunneling to allow the remote programs to create windows on the display of the system which starts the program. Unless this behavior is changed, all windows will show up on one display and most probably overlap. Our solution to these problems is:

1. to create a default login on all nodes which sets the necessary variables (for example by creating/modifying .Xauthority -better solution- or using xhost +localhost -less secure solution-),
2. on each process, set a DISPLAY variable which depends on where the process is running and if necessary, set-up authorization in a a start-up file which belongs to the user which starts the MPI job (for example .bashrc, .cshrc or equivalent, note that .login and .profile are not always executed when the shell is not interactive)

In the next release, ParaView will support Mesa off-screen rendering.

## Windows Related Issues

In some MPI implementations, the remote tasks started by the MPI system are not allowed to interact with the desktop. Unless this is changed, ParaView can not function. The solution to this problem is implementation dependent and usually involves changing the setting of the service responsible of starting processes and sometimes recompiling the service (obviously not an option if no source code is available).

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Last modified: Mon Dec 3 13:19:19 EST 2001