Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster

提交懂到hadoop的任务总是报：Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster

经过检查发现，在日志中有明确的提示：

Error: Could not find or load main class org.apache.hadoop.mapreduce.v2.app.MRAppMaster

Please check whether your etc/hadoop/mapred-site.xml contains the below configuration:

<property>

<name>yarn.app.mapreduce.am.env</name>

<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>

</property>

<property>

<name>mapreduce.map.env</name>

<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>

</property>

<property>

<name>mapreduce.reduce.env</name>

<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>

</property>

需要在mapred-site.xml中增加

<property>

<name>yarn.app.mapreduce.am.env</name>

<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>

</property>

<property>

<name>mapreduce.map.env</name>

<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>

</property>

<property>

<name>mapreduce.reduce.env</name>

<value>HADOOP_MAPRED_HOME=${full path of your hadoop distribution directory}</value>

</property>

增加后重启yarn的resourcemanager和nodemanager，任务就可以正常运行了。