部署hdfs 、yarn HA后， 启动之。
在启动 JobHistoryServer时， 报错如下：

18/05/07 16:55:21 INFO impl.MetricsSystemImpl: JobHistoryServer metrics system shutdown complete.
18/05/07 16:55:21 FATAL hs.JobHistoryServer: Error starting JobHistoryServer
java.lang.RuntimeException: java.io.IOException: Incomplete HDFS URI, no host: hdfs://hm_cluster
        at org.apache.hadoop.fs.FileContext.getFileContext(FileContext.java:469)
        at org.apache.hadoop.fs.FileContext.getFileContext(FileContext.java:490)
        at org.apache.hadoop.mapreduce.v2.jobhistory.JobHistoryUtils.getDefaultFileContext(JobHistoryUtils.java:247)
        at org.apache.hadoop.mapreduce.v2.jobhistory.JobHistoryUtils.ensurePathInDefaultFileSystem(JobHistoryUtils.java:277)
        at org.apache.hadoop.mapreduce.v2.jobhistory.JobHistoryUtils.getConfiguredHistoryServerDoneDirPrefix(JobHistoryUtils.java:224)
        at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.tryCreatingHistoryDirs(HistoryFileManager.java:673)
        at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.createHistoryDirs(HistoryFileManager.java:633)
        at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.serviceInit(HistoryFileManager.java:594)
        at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
        at org.apache.hadoop.mapreduce.v2.hs.JobHistory.serviceInit(JobHistory.java:95)
        at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
        at org.apache.hadoop.service.CompositeService.serviceInit(CompositeService.java:107)
        at org.apache.hadoop.mapreduce.v2.hs.JobHistoryServer.serviceInit(JobHistoryServer.java:154)
        at org.apache.hadoop.service.AbstractService.init(AbstractService.java:163)
        at org.apache.hadoop.mapreduce.v2.hs.JobHistoryServer.launchJobHistoryServer(JobHistoryServer.java:229)
        at org.apache.hadoop.mapreduce.v2.hs.JobHistoryServer.main(JobHistoryServer.java:239)

经查： hdfs路径名中不能出现下划线 。