提交 MapReduce 任務到 YARN 上執行，報錯：

Error: org.apache.hadoop.mapreduce.task.reduce.Shuffle2.run(YarnChild.java:164)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1924)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:158)
Caused by: java.io.IOException: Exceeded MAX_FAILED_UNIQUE_FETCHES; bailing-out.
at org.apache.hadoop.mapreduce.task.reduce.ShuffleSchedulerImpl.checkReducerHealth(ShuffleSchedulerImpl.java:392)
at org.apache.hadoop.mapreduce.task.reduce.ShuffleSchedulerImpl.copyFailed(ShuffleSchedulerImpl.java:307)
at org.apache.hadoop.mapreduce.task.reduce.Fetcher.copyFromHost(Fetcher.java:366)
at org.apache.hadoop.mapreduce.task.reduce.Fetcher.run(Fetcher.java:198)
查看日志后，發現具體報錯如下：

yarn.nodemanager.local-dirs配置錯誤報錯.png

解決方法：

# yarn.nodemanager.local-dirs對應的路徑必須在hdfs-site.xml中的hadoop.tmp.dir路徑下，否則yarn會報錯找不到緩存文件

<property>

    <name>yarn.nodemanager.local-dirs</name>

    <value>hadoop.tmp.dir/nm-local-dir</value>

</property>