loryza/narwal-dev repository overview

     shifterimg -v pull docker:loryza:nersc-bench:latest```

This means that you're pulling from [hub.docker.com](https://hub.docker.com), from user or group named ```loryza```, the repo ```nersc-bench``` with tag ```latest```.  Depending on how large your docker image is, that will take a few minutes.  When you check by rerunning the ```shifterimg -v pull docker:loryza:nersc-bench:latest``` command, it should return something like this to indicate that it is **READY** for use.

  Message: {
    "ENTRY": null,
    "ENV": [
      "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
      "PETSC_VERSION=3.6.3",
      "SLEPC_VERSION=3.6.2",
      "SLEPC_DIR=/usr/local",
      "PETSC_DIR=/usr/local",
      "SWIG_VERSION=3.0.7",
      "TRILINOS_VERSION=12.4.2"
    ],
    "WORKDIR": "MISSING",
    "groupAcl": [],
    "id": "52f68847b6f41f193206587272e4c75cd5b00c36a701f540093c27c6a66cefa4",
    "itype": "docker",
    "last_pull": 1455235653.600452,
    "status": "READY",
    "system": "cori",
    "tag": [
      "loryza:nersc-bench:latest"
    ],
    "userAcl": []
  }

There's an MPI enabled C++ demo named ```demo_poisson``` compiled and installed in ```/usr/local/bin```.  To run it on 2 Cori nodes (that's 32 cores), a SLURM batch file like this should work:

  #!/bin/bash
  #SBATCH --image=docker:loryza:nersc-bench:latest
  #SBATCH -N 2
  #SBATCH -p debug
  #SBATCH -t 00:05:00
  shifter --image=docker:loryza:nersc-bench:latest mpirun -np 32 demo_poisson

A quick line-by-line translation:

* bash shell, please
* using a docker image
* using 2 nodes
* request 5 minutes of wall time
* run via shifter, in that docker image, the compiled executable ```demo_poisson```  using ```mpirun``` across 32 cores.

To submit the job via SLURM

  sbatch demo_poisson.sl


Now wait for your job to complete :)  When the job completes, it will dump out the output files (in this case a PVD file and a bunch of VTU files) into the directory from which the batch file was launched.