title: What is the difference and relationship between mpirun, mpiexec and mpiexec.hydra?
body: <p>I got confused about 3 things: mpirun, mpiexec and mpiexec.hydra</p>
  
  <p>On my cluster, all of them exist, and all of them belong to intel. </p>
  
  <p>What is the difference and relationship between them? Especially, what on earth is mpiexec.hydra? Why there is a dot between mpiexec and hydra, what does it mean?</p>