I have a C++ code, test.cpp, and am using OpenMPI when running it. I followed the instructions here and it appears to have called OpenMPI correctly. I can compile and run the code perfectly fine from the command line but I just have to specify "TMPDIR=/tmp" before running it, i.e.: $ mpic++ -std=c++11 test.cpp $ TMPDIR=/tmp mpirun -np 4 a.out But when I try to run the code in XCode (based on the above instructions), it tells me that there are no build issue but then comes up with the error: orterun was unable to launch the specified application as it could not access or execute an executable: Thus I am simply wondering how I can ensure that XCode uses the directory "TMPDIR=/tmp" when executing the file (I believe that's where the problem is arising). I have tried specifying it in the "Edit Schemes" options although perhaps I am making an error.