Hello, I have been working with the MPI_Comm_spawn function, which was working fine for a simple compiled version of MPICH 3.4.1, where in the *configure* step it only has the "--prefix" argument. However, when this function was called with another compiled version of MPICH 3.4.1 which uses Infiniband, an error arised. Am I missing some arguments in the compilation step of MPICH when using UCX? Here is the output of *mpichversion*: $ mpichversion MPICH Version: 3.4.1 MPICH Release date: Fri Jan 22 14:17:48 CST 2021 MPICH Device: ch4:ucx MPICH configure: --prefix=/soft/gnu/mpich-3.4.1-ucx --with-device=ch4:ucx --with-ucx=/soft/gnu/ucx-1.11 MPICH CC: gcc -O2 MPICH CXX: g++ -O2 MPICH F77: gfortran -O2 MPICH FC: gfortran -O2 MPICH Custom Information: The following is the information about the minimal code which arises the error Source: https://www.rookiehpc.com/mpi/docs/mpi_comm_spawn.php Compiling: mpicc mpi_spawn.c Running: mpirun -np 2 ./a.out We are processes spawned directly by you, we now spawn a new instance of an MPI application. We are processes spawned directly by you, we now spawn a new instance of an MPI application. Assertion failed in file src/mpid/ch4/src/ch4_init.c at line 651: MPIR_Process.comm_parent != NULL /soft/gnu/mpich-3.4.1-ucx/lib/libmpi.so.12(MPL_backtrace_show+0x39) [0x7fe15d506d41] /soft/gnu/mpich-3.4.1-ucx/lib/libmpi.so.12(+0x32eaa8) [0x7fe15d4a6aa8] /soft/gnu/mpich-3.4.1-ucx/lib/libmpi.so.12(+0x3602f8) [0x7fe15d4d82f8] /soft/gnu/mpich-3.4.1-ucx/lib/libmpi.so.12(+0x225803) [0x7fe15d39d803] /soft/gnu/mpich-3.4.1-ucx/lib/libmpi.so.12(PMPI_Init+0xa8) [0x7fe15d39d598] ./a.out(+0x123e) [0x55ece110a23e] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x7fe15cfa10b3] ./a.out(+0x114e) [0x55ece110a14e] Abort(1) on node 0: Internal error