Uhh, never mind, a minute after hitting Send I realized I was using an older MPICH by mistake. This doesnt work in 3.0.x but works in 3.3. The HYDRA_LAUNCHER_EXTRA_ARGS is not needed either. saurabh From: Saurabh T Sent: Wednesday, February 6, 2019 1:44 PM To: [email protected] Subject: Enabling X11 apps with MPICH 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