[Mpi-comments] On the use of environment variables

[Bruno Kinoshita]

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 <niethammer at hlrs.de>
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/environment-var.html__;!!G_uCfscf7eWS!erPFxKiH0jAFWnMKq8SzdbLa1nx5BBaH0ku_rMUda0GRCJ_H8tt7AMIdikdMoYvvVjLlh8gqg_w5-Z-O4eismCaoEm9lm9HA2NA$ 
>   - Variables used to control the wrapper compilers:
> https://urldefense.us/v3/__https://docs.open-mpi.org/en/v5.0.x/building-apps/customizing-wrappers.html__;!!G_uCfscf7eWS!erPFxKiH0jAFWnMKq8SzdbLa1nx5BBaH0ku_rMUda0GRCJ_H8tt7AMIdikdMoYvvVjLlh8gqg_w5-Z-O4eismCaoEm9lNEt3DxI$ 
>   - Variables to control MCA parameters:
> https://urldefense.us/v3/__https://docs.open-mpi.org/en/v5.0.x/mca.html*environment-variables__;Iw!!G_uCfscf7eWS!erPFxKiH0jAFWnMKq8SzdbLa1nx5BBaH0ku_rMUda0GRCJ_H8tt7AMIdikdMoYvvVjLlh8gqg_w5-Z-O4eismCaoEm9lcY1zaGA$ 
> * 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/intro_mpi_ucx.html__;!!G_uCfscf7eWS!erPFxKiH0jAFWnMKq8SzdbLa1nx5BBaH0ku_rMUda0GRCJ_H8tt7AMIdikdMoYvvVjLlh8gqg_w5-Z-O4eismCaoEm9l8uKI-Nc$ 
> * 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.html__;!!G_uCfscf7eWS!erPFxKiH0jAFWnMKq8SzdbLa1nx5BBaH0ku_rMUda0GRCJ_H8tt7AMIdikdMoYvvVjLlh8gqg_w5-Z-O4eismCaoEm9lN3BTFl8$ 
>
>
>
> ----- Original Message -----
> From: "Bruno Kinoshita via mpi-comments" <mpi-comments at lists.mpi-forum.org
> >
> To: "mpi-comments" <mpi-comments at lists.mpi-forum.org>
> Cc: "Bruno Kinoshita" <brunodepaulak at gmail.com>
> 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
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> 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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>
>
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