Install mpiexecjl
You can install mpiexecjl with MPI.install_mpiexecjl(). The default destination directory is joinpath(DEPOT_PATH[1], "bin"), which usually translates to ~/.julia/bin, but check the value on your system. You can also tell MPI.install_mpiexecjl to install to a different directory.
Enter Julia and write:
$ julia
julia> using MPI
julia> MPI.install_mpiexecjl()
To quickly call this wrapper we recommend you to add the destination directory to your PATH environment variable.