连接hadoop集群或 Error: Call From hadoop/127.0.1.1 to localhost:8020 failed on connection exception: java
来源：华佗小知识
出错:
Error: Call From hadoop/127.0.1.1 to localhost:8020 failed on connection exception: java.net.ConnectException: 拒绝连接: For more details see: http://wiki.apache.org/hadoop/ConnectionRefused
