Hi, I am unable to get executables that open a GUI window working with MPICH. OpenMPI works fine: orterun --mca plm_rsh_agent "ssh -X -n" -np 3 xcalc brings up 3 xcalc windows. In MPICH (latest stable version 3.3), I tried HYDRA_LAUNCHER_EXTRA_ARGS="-X -n" mpiexec -np 3 xcalc but this fails with: X11 connection rejected because of wrong authentication. Error: Can't open display: localhost:10.0 Note: default hosts in both cases are the same and not the current machine. Does MPICH not allow X apps? saurabh