Segfaults with OpenMPI 2.1.1
Ubuntu 18.04 has OpenMPI 2.1.1 as its default. This version has bug in its MPI/IO routines in combination with a Cartesian communicator: https://github.com/open-mpi/ompi/issues/3695. The bug only occurs when using a 3D block grid (https://github.com/paboyle/Grid/issues/125). This behavior has been observed by @ca36xymo, whose 2D simulations run fine while the 3D simulations segfault.