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

原因：yarn-site.xml 中，yarn.application.classpath 未配置

解决：其中 hadoop 版本对应更改

    <property>
        <name>yarn.application.classpath</name>
        <value>
            /opt/hadoop-3.1.0/etc/hadoop,
            /opt/hadoop-3.1.0/share/hadoop/common/*,
            /opt/hadoop-3.1.0/share/hadoop/common/lib/*,
            /opt/hadoop-3.1.0/share/hadoop/hdfs/*,
            /opt/hadoop-3.1.0/share/hadoop/hdfs/lib/*,
            /opt/hadoop-3.1.0/share/hadoop/mapreduce/*,
            /opt/hadoop-3.1.0/share/hadoop/mapreduce/lib/*,
            /opt/hadoop-3.1.0/share/hadoop/yarn/*,
            /opt/hadoop-3.1.0/share/hadoop/yarn/lib/*
        </value>
    </property>