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 <discuss@mpich.org>
Sent: Thursday, June 11, 2026 8:50 AM
To: discuss@mpich.org <discuss@mpich.org>
Cc: John Cary <cary@colorado.edu>
Subject: [mpich-discuss] How to get srun/mpich to use the right interface?

This Message Is From an External Sender

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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