This is exactly what I needed. Thank you so much for the answer, pointers and links, Christoph! Best regards Bruno On Wed, 18 Mar 2026 at 10:42, Christoph Niethammer <[email protected]> wrote:

Dear Bruno,

As you correctly noted, the MPI Standard does not define and make any environment variables mandatory for implementations. This differs from, e.g., OpenMP, which specifies several environment variables to control aspects such as the number of threads or thread binding. [1]

That said, MPI implementations, and the communication libraries they use under the hood (e.g., UCX), commonly use environment variables to control various runtime behaviors and tuning parameters.

Here some pointers if you want to explore this further: * Open MPI: - Variables set by Open MPI: https://urldefense.us/v3/__https://docs.open-mpi.org/en/main/tuning-apps/env... - Variables used to control the wrapper compilers: https://urldefense.us/v3/__https://docs.open-mpi.org/en/v5.0.x/building-apps... - Variables to control MCA parameters: https://urldefense.us/v3/__https://docs.open-mpi.org/en/v5.0.x/mca.html*envi... * MPICH: - READMES and the mpiexec man pages of mpich - Variables in the HPE MPICH documentation: https://urldefense.us/v3/__https://cpe.ext.hpe.com/docs/24.07/mpt/mpich/intr... * UCX: - You can list all variables via the command `ucx_info -f`

Best regards Christoph Niethammer

[1] https://urldefense.us/v3/__https://www.openmp.org/spec-html/5.2/openmpch21.h...

----- Original Message ----- From: "Bruno Kinoshita via mpi-comments" <[email protected]

...

To: "mpi-comments" <[email protected]> Cc: "Bruno Kinoshita" <[email protected]> Sent: Tuesday, 17 March, 2026 21:46:59 Subject: [Mpi-comments] On the use of environment variables

Hello, I am working on a masters thesis about workflows with CWL and MPI. The workflows I am working with can be executed with tools (CWL runners) that try to isolate the execution of each step. This isolation can be done, for instance, with ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message came from outside your organization. ZjQcmQRYFpfptBannerEnd Hello,

I am working on a masters thesis about workflows with CWL and MPI. The workflows I am working with can be executed with tools (CWL runners) that try to isolate the execution of each step.

This isolation can be done, for instance, with containers. When using the containers, some CWL runners normally remove all environment variables (e.g., with --cleanenv with Singularity).

Before passing all variables from the host or creating a wrapper script to control which variables are sent, I am searching for confirmation that the environment variables used in MPI implementations are not defined in the standard.

I read parts of the MPI 5.0 specification, and I could only find environment variables being mentioned as one of the possible mechanisms to solve some sort of problem. So my understanding right now is that the MPI specification does not say implementations MUST use environment variables, only they MAY.

Could anyone please confirm this? This is my first message in the list; I hope I am posting in the right place. If not, I apologize.

Thank you,

Bruno

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