提交 MapReduce 任务到 YARN 上执行，报错：

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，发现具体报错如下：

yarn.nodemanager.local-dirs配置错误报错.png

解决方法：

# yarn.nodemanager.local-dirs对应的路径必须在hdfs-site.xml中的hadoop.tmp.dir路径下，否则yarn会报错找不到缓存文件

<property>

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

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

</property>