MPI 程序仅在一个进程中执行，而不是在多个进程中请求

Question

I am a beginner trying to learn MPI. I have tried to run the following program downloaded from internet:

    #include <stdio.h>
    #include <mpi.h>

    int main (argc, argv)
         int argc;
         char *argv[];
    {
      int rank, size;

      MPI_Init (&argc, &argv);  /* starts MPI */
      MPI_Comm_rank (MPI_COMM_WORLD, &rank);    /* get current process id */
      MPI_Comm_size (MPI_COMM_WORLD, &size);    /* get number of processes */
      printf( "Hello world from process %d of %d\n", rank, size );
      MPI_Finalize();
      return 0;
    }

The code has been compiled with mpicc and executed with mpirun .

mpicc HelloWorld.c
mpirun -np 4 a.out

The output is as follows:

Hello world from process 0 of 1
Hello world from process 0 of 1
Hello world from process 0 of 1
Hello world from process 0 of 1

My question is, why the output has generated only one process and not 4 processes as requested?

Answer 1

This problem occurs when mpicc and mpirun are not from the same MPI Implementation.
You can do uninstall openmpi and mpich and install only mpich lib.

Run these commands in your terminal.
sudo apt-get remove --auto-remove openmpi-bin
sudo apt-get remove --auto-remove mpich
sudo apt-get install mpich

Answer 2

The following solved my problem:

sudo apt-get remove --auto-remove openmpi-bin
sudo apt-get remove --auto-remove mpich
sudo apt-get install mpich
sudo apt install lam-runtime     
sudo apt install mpich           
sudo apt install openmpi-bin     
sudo apt install slurm-wlm-torque