MPI

# Note: Do not install or use the openmpi package, as it has issues.
apt update && apt-get install mpich

# Execute the `ls` command using MPI to see if it can output directories and files.
mpirun -n 2 ls

# Create a file named `test.c` with the following content:
#include <stdio.h>
#include <mpi.h>
int main (int argc, char** argv) {
    int size, rank;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    printf("size = %d rank = %d\n", size, rank);
    MPI_Finalize();
}

# Compile the code to generate an executable file named `a.out`.
mpicc test.c

# Run the executable. Note that you need to use the absolute path since `a.out` is not in the PATH environment variable. For example, if the test directory is `/root`:
mpirun -n 1 /root/a.out