• Apptainer
  • About the images
• Creating an OpenFOAM apptainer image
  • Notes
• Running OpenFOAM in an apptainer
  • Running interactively
  • Running non-interactively

Apptainer

Apptainer (formerly known as singularity) is a container image system favoured on HPC systems.

For those already familar with docker or podman containers, apptainer uses a slightly different approach:

• Runs without elevated (root) privileges
• Images are saved as physical files to disk

About the images

For overall flexibility, the OpenFOAM apptainer support is provided via description files in the packaging/containers repository rather than pre-assembled images. The download bandwidth will be essentially identical in both cases.

The packages do not contain visualization (eg, ParaView/runTimePostProcessing) or external-solver (eg, PETSc) modules:
see the corresponding FAQ

Creating an OpenFOAM apptainer image

Creating an apptainer image is a simple as downloading the container description files from the packaging/containers repository.

Select and edit the definitions to suit your purposes and build the image. For example,

apptainer build --fakeroot openfoam2406.sif openfoam-run_rocky.def

which will build the file openfoam2406.sif from the image description file, using the RockyLinux base image. A .sif extension (singularity image format) is often used for the apptainer files but is not required.

Notes

It is recommended to base OpenFOAM apptainer images on the framework provided by the packaging/containers repository. In addition to providing the plain sequencing of package installation, the included file assets (openfoam-files.rc/) provide for a coherent runtime environment with the OpenFOAM environment properly initialised.

Running OpenFOAM in an apptainer

Running OpenFOAM in an apptainer is absolutely straight forward. Simply place the generated apptainer file somewhere convenient in your path (eg, $HOME/bin etc) and use it.

For example,

$ openfoam2406.sif

This will open an interactive shell with the OpenFOAM environment active, with the current local directory mounted within the container.

Running interactively

Running an interactive shell with the OpenFOAM environment active is the default behaviour for the image and the internal run-script.

For example,

$ openfoam2406.sif

Running non-interactively

It is also possible to use the image in batch mode. For example,

$ openfoam2406.sif blockMesh -help

It is also possible to use as for running shell scripts. For example,

$ openfoam2406.sif -c './Allrun'

Note that the entry point within the image itself also has some option handling. For example,

$ openfoam2406.sif -help

Copyright (C) 2022-2024 OpenCFD Ltd.