environment variables

The variables must be set for starting

DMLC_NUM_WORKER : the number of workers
DMLC_NUM_SERVER : the number of servers
DMLC_ROLE : the role of the current node, can be worker, server, or scheduler
DMLC_PS_ROOT_URI : the ip or hostname of the scheduler node
DMLC_PS_ROOT_PORT : the port that the scheduler node is listening
DMLC_WORKER_ID : the rank of the worker

additional variables:

DMLC_INTERFACE : the network interface a node should use. in default choose automatically
DMLC_LOCAL : runs in local machines, no network is needed