HI John, Try using the UCX instead of libfabric. You can configure MPICH with ./configure --with-device=ch4:ucx to use UCX. With libfabric, could you try set environment variable FI_PROVIDER=verbs ? If you still have issue, try run a dummy MPI program setting `MPIR_CVAR_DEBUG_SUMMARY=1`. That will provide more logging details on which libfabric provider is being selected. -- Hui Zhou ________________________________ From: John Cary via discuss <[email protected]> Sent: Thursday, June 11, 2026 8:50 AM To: [email protected] <[email protected]> Cc: John Cary <[email protected]> Subject: [mpich-discuss] How to get srun/mpich to use the right interface? How to get mpich to use the right interface? mpich configured and built with libfabric as shown below.  It is run using slurm (srun).  The result is [1781142435. 559314543] ne07: rank64. vorpal: Failed to modify UD QP to INIT on mlx5_0: Operation ZjQcmQRYFpfptBannerStart This Message Is From an External Sender This message came from outside your organization. ZjQcmQRYFpfptBannerEnd How to get mpich to use the right interface? mpich configured and built with libfabric as shown below. It is run using slurm (srun). The result is [1781142435.559314543] ne07:rank64.vorpal: Failed to modify UD QP to INIT on mlx5_0: Operation not permitted [1781142435.563376291] ne07:rank66.vorpal: Failed to modify UD QP to INIT on mlx5_0: Operation not permitted Abort(203572367): Fatal error in internal_Init: Other MPI error, error stack ... which I think means that mpich is txrying to run over the mlx5_0 interface, which does not exist. The interfaces are eno1: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500 eno2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500 ib0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 2044 lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 and we want to use ib0, infiniband. We tried export HYDRA_IFACE=ib0 srun ... and got the same error. How can srun/mpich be instructed to use the ib0 interface by default? Also, how can one see which interface mpich is choosing? Thx... '/user/builds-linux-centos8-zen2/gvxsimall/mpich-5.0.1/configure' \ --prefix=/home/research/user/installs/linux-centos8-zen2/contrib-gcc1140/mpich-5.0.1-shared \ --enable-shared \ --disable-static \ CC='/home/common/gcc-11.4.0/bin/gcc' \ CXX='/home/common/gcc-11.4.0/bin/g++' \ FC='/home/common/gcc-11.4.0/bin/gfortran' \ F77='/home/common/gcc-11.4.0/bin/gfortran' \ CFLAGS='-pthread -pipe -fPIC' \ CXXFLAGS='-pthread -Wno-deprecated-declarations -pipe -fPIC' \ FFLAGS='-fallow-argument-mismatch -pipe -fPIC' \ FCFLAGS='-fallow-argument-mismatch -pipe -fPIC' \ LDFLAGS='-L/home/common/gcc-11.4.0/lib64 -Wl,-rpath,/home/common/gcc-11.4.0/lib64' \ LDSHARED='-L/home/common/gcc-11.4.0/lib64 -Wl,-rpath,/home/common/gcc-11.4.0/lib64' \ --with-libfabric=install \ --with-device=ch4:ofi \ --without-cuda \ --disable-gl