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