Hi Hui, I tried setting LIBRARY_PATH to /lib64 but that didn’t help (neither did setting it /usr). I’m attaching the build logs again (the build-env logs do indeed confirm that LIBRARY_PATH was set). I tried building MPICH against my own pmix library and everything works. (But this pmix is local to my home directory and not linked to slurm). Inspecting the build-env log from the successful build, I see that the libevent’s location is absent from LIBRARY_PATH but is present in the SPACK_INCLUDE/LINK/RPATH_DIRS (and also in pkg-config/cmake paths which I’m guessing isn’t relevant here) which are used by spack’s compiler wrapper to ensure correct include/link/rpath settings. My task right now is to test the installation of mpi libraries with pmix/ucx on a small test cluster before we deploy it on the production cluster at my campus so it’s not of the highest concern to me that MPICH won’t link to a pmix library that doesn’t have rpaths enabled. I’ll ask the sysadmins to rebuild pmix with rpath support and try if that works. If it does, I’ll reply to this thread either asking for help again or indicating that it succeeds (whereby it can (hopefully) serve as a reference for others facing the same issue in the future). Thank You, Sajid Ali | PhD Candidate Applied Physics Northwestern University s-sajid-ali.github.io