Setting up a ParaView Server

ParaView is designed to work well in client/server mode. In this way, users can have the full advantage of using a shared remote high-performance rendering cluster without leaving their offices. This document is designed to help get you started with build and setting up your own ParaView server. It also serves as a collection point for the "tribal knowledge" acquired to make parallel rendering and other aspects of parallel and client/server processing most efficient.

Compiling

Ideally, we would like to provide precompiled binaries of ParaView for all of our users to make installing it more convenient. Unfortunately, the large variety hardware, operating systems, and MPI implementations makes this task impossible. Thus, if you wish to use ParaView on a parallel server, you will have to compile ParaView from source.

After downloading ParaView, follow the Building and Installation instructions. When following these instructions, be sure to compile in MPI support by setting the PARAVIEW_USE_MPI CMake flag to ON and setting the appropriate paths to the MPI include directory and libraries.

One problem many people face when compiling with MPI is that their MPI implementation provides multiple libraries, many of which are required when compiling ParaView. If there are only two such libraries, you can add them separately in the MPI_LIBRARY and MPI_EXTRA_LIBRARY CMake variables. If you need to link in more than two libraries, you can specify multiple libraries in the MPI_LIBRARY variable by separating them with semicolons (;). You can apply the same trick to the MPI_INCLUDE_PATH to specify several include directories.

Another problem sometimes encountered is the lack of graphics libraries. There are many circumstances where you would want to compile the ParaView server on a parallel computer with no graphics hardware and thus no OpenGL implementation. In this case, most people use the Mesa 3D Graphics Library, which is a portable, software-only implementation of the OpenGL API. A cluster built using a Linux operating system probably already has a version of Mesa installed, but otherwise you can always download the source code from http://mesa3d.org.

OSMesa support

One of the most difficult problems people face when installing a ParaView server is establishing XConnections. This whole problem can be circumvented by using the OSMesa library. However, Mesa is strictly a CPU rendering library so, use the OSMesa solution if and only if your server hardware does not have rendering hardware. If your cluster does not have graphics hardware, then compile ParaView with OSMesa support and use the --use-offscreen-rendering flag when launching the server.

The first step to compiling OSMesa support is to make sure that you are compiling with the Mesa 3D Graphics Library. It is difficult to tell an installation of Mesa from any other OpenGL implementation (although the existance of an osmesa.h header and a libOSMesa library is a good clue). If you are not sure, you can always download your own copy from http://mesa3d.org.

Now set the CMake variable OPENGL_INCLUDE_DIR to point to the Mesa include directory (the one containing the GL subdirectory), and set the OPENGL_gl_LIBRARY and OPENGL_glu_LIBRARY to the libGL and libGLU library files, respectively. Next, change the VTK_OPENGL_HAS_OSMESA variable to ON. After you configure again you will see a new CMake variable called OSMESA_LIBRARY. Set this to the libOSMesa library file. After you configure and generate your makefiles, you should be ready to build with OSMesa support.

Once again, once you build with OSMesa support, it will not take effect unless you launch the server with the --use-offscreen-rendering flag.

Please be aware that OSMesa support is not the same thing as mangled Mesa (although they are often used for the same thing). Mangled Mesa is harder to set up and we (at Sandia National Laboratories) have not found it to be useful. Mangled Mesa provides a mechanism to use either hardware acceleration or CPU-only rendering. Some organizations use this to provide a single build for multiple servers, some with and some without hardware rendering. We find it easier to simply provide a separate build for each server.

Running the Server

X Connections

One of the most common problems people have with setting up the ParaView server is allowing the server processes to open windows on the graphics card on each process's node. When ParaView needs to do parallel rendering, each process will create a window that it will use to render. This window is necessary because you need the X window before you can create an OpenGL context on the graphics hardware.

There is a way around this. If you are using the Mesa as your OpenGL implementation, then you can also use the supplemental OSMesa library to create an OpenGL context without an X window. However, Mesa is strictly a CPU rendering library so, use the OSMesa solution if and only if your server hardware does not have rendering hardware. If your cluster does not have graphics hardware, then compile ParaView with OSMesa support and use the --use-offscreen-rendering flag when launching the server.

Assuming that your cluster does have graphics hardware, you will need to establish the following three things.

1. Have xdm run on each cluster node at startup. Although xdm is almost always run at startup on workstation installations, it is not as commonplace to be run on cluster nodes. Talk to your system administrators for help in setting this up.
2. Disable all security on the X server. That is, allow any process to open a window on the x server without having to log in. Again, talk to your system administrators for help.
3. Make sure each process is run with the DISPLAY environment variable set to localhost:0 (or just :0).

To enable the last condition, it is often helpful to use the env program in the mpirun call. So you would have something like

miprun -np 4 /bin/env DISPLAY=localhost:0 ./pvserver

An easy way to test your setup is to use the glxgears program. Unlike pvserver, it will quickly tell you (or, rather, fail to start) if it cannot connect to the local server.

mpirun -np 4 /bin/env DISPLAY=localhost:0 /usr/X11R6/bin/glxgears

Pitfalls

Here we capture the most common problems people run into with setting up client/server.

Specifying multiple MPI include directories

You can add multiple directories to the MPI_INCLUDE_PATH CMake variable by separating them with semicolons (;). See the #Compiling section for more details.

Specifying multiple MPI libraries

You can use both the MPI_LIBRARY and MPI_EXTRA_LIBRARY CMake variables for specifying MPI libraries. You can also add multiple libraries to MPI_LIBRARY by separating the files with semicolons (;). See the #Compiling section for more details.