This image is a relocatable and renamable file, which is recommended to be placed in a dedicated directory for easy retrieval; this directory can be any, and for the purposes of this tutorial, we assume you have placed it in a directory named $HOME/apptainer-images:

mkdir -p $HOME/apptainer-images
mv paraview.sif $HOME/apptainer-images/paraview.sif

To illustrate the functioning of the visualization program, a set of files readable with ParaView is available in archive form via this link. This archive contains the following files:

• tutorial-disk.ex2, one of the example files provided by default with ParaView containing the structure of a hollow cylinder in the ex2 format, typically used with the ExodusII finite element code.
• tutorial-can.ex2, also provided by default with ParaView, which allows reproducing the evolution of a cylindrical object (such as a can) crushed by a blunt object.

In this tutorial, we assume that the input files contained in this archive are in the current directory:

tar -xzf DIAMOND-tutorial.tar.gz # Extracts the contents of the archive, creating ./tutorial
cd ./tutorial

One-line command

For those in a hurry, here’s how to launch the ParaView visualization tool using the container image (downloaded beforehand and located at $HOME/apptainer-images/paraview.sif). In case the current directory contains a file readable by ParaView:

apptainer run $HOME/apptainer-images/paraview.sif <input.file>

Detail of using the ParaView container

This section presents the various ways to use the ParaView image. For more details on Apptainer commands, please refer to this tutorial.

To run ParaView without any containerization, one would use the command:

paraview <input.file.1> <input.file.2> ...

where the input files input.file.* are optional and allow loading the structure(s) that you want to display directly upon application launch. Note

To display the loaded data, you need to apply visual rendering by clicking the Apply button in the Properties panel appearing on the left.

With Apptainer, the operation is similar, with a few differences:

• you need to call Apptainer to launch the container (a command line).
• if you want to isolate the container from your machine, then you need to ensure access to the files you want to load in ParaView (two options in the previous command line).
• you need to ensure, if necessary, that the container has access to the graphical resources of the host machine (another option).

Each of these points is detailed in the following sections.

Launching the ParaView container with Apptainer

To launch a command in an Apptainer container, you can use apptainer exec <image name> <command>, to which you can add options detailed in the following sections. In our case, where the image is located at the path $HOME/apptainer-images/paraview.sif, and where the command is of the form paraview tutorial-disk.ex2 with the configuration file tutorial-disk.ex2 in the current directory, we can do:

apptainer exec $HOME/apptainer-images/paraview.sif paraview tutorial-disk.ex2

This command works as follows:

• creation of a container from the Apptainer image $HOME/apptainer-images/paraview.sif.
• execution, within this container, of the command paraview tutorial-disk.ex2. A ParaView window then appears, with which you can interact as you would normally if ParaView were installed on your machine.
• once the application usage is finished (i.e., when you close the ParaView window), the container is destroyed and resources are released.

We can replicate the same behavior with apptainer run which directly calls the default command of the image, paraview, to which arguments can be added.

apptainer run $HOME/apptainer-images/paraview.sif tutorial-disk.ex2 # the "paraview" command is implicitly called.

Finally, you can directly call the image as an executable, which is strictly identical to using apptainer run (for the sake of formality, let’s change the configuration file).

$HOME/apptainer-images/paraview tutorial-can.ex2

Isolation between the container and the host machine

By default, Apptainer does not fully isolate the container from the host machine’s system; for partial or total isolation, respectively, the --no-mount or --no-home and --containall flags should be used (see this link for more information). In cases where the --containall option is activated, we encounter two difficulties.

Sharing graphical resources

On one hand, it is possible that an error message appears, informing you that one of the library plugins (qt.qpa.xcb) fails to connect to your display resources.

apptainer run --containall $HOME/apptainer-images/paraview.sif
[...]
qt.qpa.xcb: could not connect to display
[...]
Aborted

This is not an incompatibility between your machine and the container: the latter is actually attempting to connect to the wrong graphical resources. This connection attempt is guided by the $DISPLAY environment variable, and the error arises because the value this variable takes within the container does not match the one it takes on your machine.

This problem is directly due to the total isolation between the container and the host machine, since in this specific case, no environment variable from your machine is transmitted to the container by Apptainer.

To circumvent this issue, simply specify to the apptainer run command (or apptainer exec) what value to assign to this environment variable within the container. For this, you can use the --env <variable>=<value> flag, as follows:

apptainer run --containall --env DISPLAY=$DISPLAY $HOME/apptainer-images/paraview.sif

File access

On the other hand, the directory containing the input files is not accessible within the container!

apptainer run --containall --env DISPLAY=$DISPLAY $HOME/apptainer-images/paraview.sif tutorial-disk.ex2
[...]
critical: Cannot open data file " "tutorial-disk.ex2" "

You must then manually mount the current directory ($PWD) to the directory where you are by default in the container ($HOME) with the --bind flag. For example:

apptainer run --containall --bind $PWD:$HOME \ # Mounts the current directory to $HOME in the container.
  $HOME/apptainer-images/paraview.sif tutorial-disk.ex2

in the case where the Paraview input files are located in the current directory ($PWD).

Note

Note that in cases where the --containall and --bind flags are used together, only the contents of the directories explicitly mounted within the container can be loaded into ParaView. Similarly, in cases where we want to export our work to an output file, these options force us to export only to the explicitly mounted directories, otherwise we may not retrieve the files when the container is destroyed if we write to non-shared directories.

Displaying help

To display the container’s help message (assuming the image is stored under $HOME/apptainer-images/paraview.sif):

apptainer run-help $HOME/apptainer-images/paraview.sif

To display the container’s metadata (code owner, version, image author, etc.):

apptainer inspect $HOME/apptainer-images/paraview.sif

Exercises

Exercise 1

How to use the container image to open ParaView?

Data

• The image is located at the following path: $HOME/apptainer-images/paraview.sif.
• Initially, we do not want to specify which configuration file to load, but we want to be able to open them later through the ParaView graphical interface, without knowing a priori where they are located on our machine.

Possible answers:

• apptainer exec $HOME/apptainer-images/paraview.sif paraview
• or apptainer run $HOME/apptainer-images/paraview.sif
• or ./$HOME/apptainer-images/paraview.sif

Note that we do not specify an input file, and we do not use any isolation (no --containall flag) to access our file tree within the container.

Exercise 2

How to visualize an animation contained in a file with a ParaView container and save this animation in avi format?

Data

• The image is located at the following path: $HOME/apptainer-images/paraview.sif
• The file containing the animation of interest is located at $PWD/tutorial-can.ex2 on the host machine.
• To display the loaded data, visual rendering needs to be applied by clicking the Apply button in the Properties panel appearing on the left.
• It is possible to interact with the Properties panel and modify the viewpoint to highlight the animation.
• Within ParaView, exporting to avi format can be done via File > Save Animation.
• We will try to provide a solution without isolating the host machine from the container, and a solution isolating the container as much as possible from the host machine.

Examples of possible answers:

• apptainer exec $HOME/apptainer-images/paraview.sif paraview tutorial-can.ex2
• or apptainer run --containall --env DISPLAY=$DISPLAY --bind $PWD:$HOME $HOME/apptainer-images/paraview.sif tutorial-can.ex2