added example of openmpi with singularity

doc.zih.tu-dresden.de/docs/software/singularity_recipe_hints.md

@@ -58,6 +58,90 @@ EOF
     ./hello
 ```
 
+### OpenMPI
+
+Definition file:
+
+```code
+Bootstrap: docker
+From: ubuntu:latest
+
+%files
+    mpitest.c /opt
+
+%environment
+    export OMPI_DIR=/opt/ompi
+    export SINGULARITY_OMPI_DIR=$OMPI_DIR
+    export SINGULARITYENV_APPEND_PATH=$OMPI_DIR/bin
+    export SINGULAIRTYENV_APPEND_LD_LIBRARY_PATH=$OMPI_DIR/lib
+
+%post
+    echo "Installing required packages..."
+    apt-get update && apt-get install -y wget git bash gcc gfortran g++ make file
+
+    echo "Installing Open MPI"
+    export OMPI_DIR=/opt/ompi
+    export OMPI_VERSION=4.0.1
+    export OMPI_URL="https://download.open-mpi.org/release/open-mpi/v4.0/openmpi-$OMPI_VERSION.tar.bz2"
+    mkdir -p /tmp/ompi
+    mkdir -p /opt
+    # Download
+    cd /tmp/ompi && wget -O openmpi-$OMPI_VERSION.tar.bz2 $OMPI_URL && tar -xjf openmpi-$OMPI_VERSION.tar.bz2
+    # Compile and install
+    cd /tmp/ompi/openmpi-$OMPI_VERSION && ./configure --prefix=$OMPI_DIR && make install
+    # Set env variables so we can compile our application
+    export PATH=$OMPI_DIR/bin:$PATH
+    export LD_LIBRARY_PATH=$OMPI_DIR/lib:$LD_LIBRARY_PATH
+    export MANPATH=$OMPI_DIR/share/man:$MANPATH
+
+    echo "Compiling the MPI application..."
+    cd /opt && mpicc -o mpitest mpitest.c
+```
+
+```code
+#include <mpi.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int main (int argc, char **argv) {
+        int rc;
+        int size;
+        int myrank, len;
+        char name[MPI_MAX_PROCESSOR_NAME];
+
+        MPI_Init (&argc, &argv);
+       
+        MPI_Comm_size (MPI_COMM_WORLD, &size);
+       
+        MPI_Comm_rank (MPI_COMM_WORLD, &myrank);
+        
+        MPI_Get_processor_name(name, &len);
+
+        fprintf (stdout, "Hello, I am rank %d/%d, at %s\n", myrank, size, name);
+
+        MPI_Finalize();
+
+        return EXIT_SUCCESS;
+
+ exit_with_error:
+        MPI_Finalize();
+        return EXIT_FAILURE;
+}
+```
+
+At your computer:
+
+```console
+sudo singularity build ubuntu_omp.sif ubuntu_omp.def
+```
+
+At ZIH systems:
+
+```console
+marie@login$ export PMIX_MCA_gds=hash
+marie@login$ srun -n 2 --time 00:10:00 singularity exec ubuntu_omp.sif /opt/mpitest
+```
+
 ### CUDA + CuDNN + OpenMPI
 
 * Chosen CUDA version depends on installed driver of host