title: how to run tensorflow distributed mnist example
body: <p>I am new to distributed tensorflow. I found this distributed mnist test in here:
  <a href="https://github.com/tensorflow/tensorflow/blob/master/tensorflow/tools/dist_test/python/mnist_replica.py" rel="noreferrer">https://github.com/tensorflow/tensorflow/blob/master/tensorflow/tools/dist_test/python/mnist_replica.py</a></p>
  
  <p>But I don't know how to make it run. I used the following script:</p>
  
  <pre><code>  python distributed_mnist.py  --num_workers=3 --num_parameter_servers=1 --worker_index=0 --worker_grpc_url="grpc://tf-worker0:2222"\
    &amp; python distributed_mnist.py  --num_workers=3 --num_parameter_servers=1 --worker_index=1 --worker_grpc_url="grpc://tf-worker1:2222"\
    &amp; python distributed_mnist.py  --num_workers=3 --num_parameter_servers=1 --worker_index=2 --worker_grpc_url="grpc://tf-worker2:2222"
  </code></pre>
  
  <p>I just found these parameters are missing, so I pass them to the program. Here is what happened:</p>
  
  <pre><code>I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcublas.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcublas.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcudnn.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcudnn.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcufft.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcufft.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcuda.so.1 locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcuda.so.1 locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcurand.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcurand.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcublas.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcudnn.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcufft.so locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcuda.so.1 locally
  I tensorflow/stream_executor/dso_loader.cc:105] successfully opened CUDA library libcurand.so locally
  Extracting /tmp/mnist-data/train-images-idx3-ubyte.gz
  Extracting /tmp/mnist-data/train-images-idx3-ubyte.gz
  Extracting /tmp/mnist-data/train-images-idx3-ubyte.gz
  Extracting /tmp/mnist-data/train-labels-idx1-ubyte.gz
  Extracting /tmp/mnist-data/t10k-images-idx3-ubyte.gz
  Extracting /tmp/mnist-data/train-labels-idx1-ubyte.gz
  Extracting /tmp/mnist-data/train-labels-idx1-ubyte.gz
  Extracting /tmp/mnist-data/t10k-images-idx3-ubyte.gz
  Extracting /tmp/mnist-data/t10k-images-idx3-ubyte.gz
  Extracting /tmp/mnist-data/t10k-labels-idx1-ubyte.gz
  Extracting /tmp/mnist-data/t10k-labels-idx1-ubyte.gz
  Extracting /tmp/mnist-data/t10k-labels-idx1-ubyte.gz
  Worker GRPC URL: grpc://tf-worker0:2222
  Worker index = 0
  Number of workers = 3
  Worker GRPC URL: grpc://tf-worker2:2222
  Worker index = 2
  Number of workers = 3
  Worker GRPC URL: grpc://tf-worker1:2222
  Worker index = 1
  Number of workers = 3
  Worker 0: Initializing session...
  Worker 2: Waiting for session to be initialized...
  Worker 1: Waiting for session to be initialized...
  E0608 20:37:13.514249023    7501 resolve_address_posix.c:126] getaddrinfo: Name or service not known
  D0608 20:37:13.514287961    7501 dns_resolver.c:189]         dns resolution failed: retrying in 15 seconds
  E0608 20:37:13.548052986    7502 resolve_address_posix.c:126] getaddrinfo: Name or service not known
  D0608 20:37:13.548091527    7502 dns_resolver.c:189]         dns resolution failed: retrying in 15 seconds
  E0608 20:37:13.555449386    7503 resolve_address_posix.c:126] getaddrinfo: Name or service not known
  D0608 20:37:13.555473898    7503 dns_resolver.c:189]         dns resolution failed: retrying in 15 seconds
  ^CE0608 20:37:28.517451603    7504 resolve_address_posix.c:126] getaddrinfo: Name or service not known
  D0608 20:37:28.517491102    7504 dns_resolver.c:189]         dns resolution failed: retrying in 15 seconds
  E0608 20:37:28.551002331    7505 resolve_address_posix.c:126] getaddrinfo: Name or service not known
  D0608 20:37:28.551029795    7505 dns_resolver.c:189]         dns resolution failed: retrying in 15 seconds
  E0608 20:37:28.556681378    7506 resolve_address_posix.c:126] getaddrinfo: Name or service not known
  D0608 20:37:28.556709728    7506 dns_resolver.c:189]         dns resolution failed: retrying in 15 seconds
  </code></pre>
  
  <p>Anyone know how to run it correctly? Thanks a lot!</p>