Getting Environment Variables Used by MPI application

[abeltre1]

Background Information

1. Open MPI Version: v5.0.0
2. Installation Method: Installed using a tarball
3. System Description:
4. Operating System/Version: Ubuntu Linux 22.04

Details of the Problem

I would like to know how to capture all the environment variables associated with an MPI application run. Specifically, is there an Open MPI variable that captures all the environment variables used to run the MPI application?

If there are specific commands or methods to retrieve these variables, please provide examples.

[jsquyres]

Are you asking from the perspective of the MPI application itself? If so, you can just use the C environ global variable to get all the environment variables and their values.

[abeltre1]

Are you asking from the perspective of the MPI application itself? If so, you can just use the C environ global variable to get all the environment variables and their values.

@jsquyres Thank you for that. How about the OpenMPI variables set for the MPI application ?

[rhc54]

Errrr...I suspect you are asking for a way to identify which envars are related to OMPI? Probably the most direct answer is to look for any envar that starts with "OMPI_". Some behavior is also controlled by envars starting with "PMIX_".

There are other envars that impact MPI behavior, but are set by 3rd parties (e.g., GPU assignments). No way to identify all of those as it depends on your local hardware, what libraries you are using, how any of those folks decide to prefix their envars, etc.

If you are asking if we provide an API or some kind of means for obtaining a list of OMPI-related envars - then no, we don't do that.

[abeltre1]

Errrr...I suspect you are asking for a way to identify which envars are related to OMPI? Probably the most direct answer is to look for any envar that starts with "OMPI_". Some behavior is also controlled by envars starting with "PMIX_".

There are other envars that impact MPI behavior, but are set by 3rd parties (e.g., GPU assignments). No way to identify all of those as it depends on your local hardware, what libraries you are using, how any of those folks decide to prefix their envars, etc.

If you are asking if we provide an API or some kind of means for obtaining a list of OMPI-related envars - then no, we don't do that.

Thank you @rhc54. I am assuming I have to do the same for SLURM environment variables ?

[rhc54]

Afraid so, yes - IIRC, they are prefixed as "SLURM_". However, those don't directly apply to the MPI app, especially if you are using "mpirun" to start the application (in which case, "mpirun" uses the Slurm envars, but no direct correlation to anything about the app). If you are using "srun", then those envars give some info as to process distribution - but don't have any direct impact on the MPI layer.

In both launch cases, the MPI lib ignores Slurm envars.