> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gpuhub.com/llms.txt
> Use this file to discover all available pages before exploring further.

# MPI

> An instructions for using MPI on Ubuntu 20.04

<Note>
  Upon testing,

  it has been observed that the Ubuntu 20.04 system operates normally,

  whereas Ubuntu 22.04 tends to hang. We recommend selecting the Ubuntu 20.04 image for use.

  The underlying cause of this issue remains unknown.

  Should you have any insights or information regarding the cause, we would greatly appreciate your feedback.

  Thank you for your cooperation and support.
</Note>

## Installation

```bash bash theme={null}
# Note: Do not install or use the openmpi package, as it has issues.
apt update && apt-get install mpich
```

## Verification

Simple Test:

```bash bash theme={null}
# Execute the `ls` command using MPI to see if it can output directories and files.
mpirun -n 2 ls

```

Compilation Test:

```bash bash theme={null}
# 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
```