hadoop报错：java.io.IOException(java.net.ConnectException: Call From xxx/xxx to xxx:10020 failed on connection exception: java.net.ConnectException: 拒绝连接

　　任务一直报错

　　现象比较奇怪，部分任务可以正常跑，部分问题报错

　　报错信息如下：

Ended Job = job_1527476268558_132947 with exception 'java.io.IOException(java.net.ConnectException: Call From xxx/xxx to xxx:10020 failed on connection exception: java.net.ConnectException: 拒绝连接; For more details see:  http://wiki.apache.org/hadoop/ConnectionRefused)'

　yarn报错，任务不能访问jobhistory，启动historyserver就行

mr-jobhistory-daemon.sh start historyserver