hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.3.jar wordcount /wcinput /wcoutput报错

执行hadoop jar share/hadoop/mapreduce/hadoop-mapreduce-examples-3.1.3.jar wordcount /wcinput /wcoutput报错

• 报错信息
  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:
  如图所示：
  
• 解决方法
  vim mapred-site.xml 添加以下内容

    yarn.app.mapreduce.am.env</name>
    HADOOP_MAPRED_HOME=/opt/module/hadoop-3.1.3</value>
</property>

    mapreduce.map.env</name>
    HADOOP_MAPRED_HOME=/opt/module/hadoop-3.1.3</value>
</property>

    mapreduce.reduce.env</name>
    HADOOP_MAPRED_HOME=/opt/module/hadoop-3.1.3</value>
</property>

如图所示
ps：所述环境变量值也为hadoop文件夹路径

• 运行成功