During training MNIST example dataset in PyTorch, I met the this RuntimeError on the Master node
File "./torch-dist/mnist-dist.py", line 201, in <module>
    init_processes(args.rank, args.world_size, run, args.batch_size, backend=args.backend)
  File "./torch-dist/mnist-dist.py", line 196, in init_processes
    dist.init_process_group(backend=backend, world_size=world_size, rank=rank, init_method="env://")
  File "/home/dl/anaconda2/envs/torch-dist-py3.6/lib/python3.6/site-packages/torch/distributed/distributed_c10d.py", line 354, in init_process_group
    store, rank, world_size = next(rendezvous(url))
  File "/home/dl/anaconda2/envs/torch-dist-py3.6/lib/python3.6/site-packages/torch/distributed/rendezvous.py", line 143, in _env_rendezvous_handler
    store = TCPStore(master_addr, master_port, start_daemon)
RuntimeError: Address already in use


It seemed that multiprocessing with launch utility had problem
I ran the code by invoking the launch utility as documentation 167 suggested
python -m torch.distributed.launch --nproc_per_node=2 --nnode=2 --node_rank=0 --master_addr='10.0.3.29' --master_port=9901 ./torch-dist/mnist-dist.py