错误描述：
[root@nna hadoop-3.2.0]# start-dfs.sh
Starting namenodes on [nna nns]
ERROR: Attempting to operate on hdfs namenode as root
ERROR: but there is no HDFS_NAMENODE_USER defined. Aborting operation.
Starting datanodes
ERROR: Attempting to operate on hdfs datanode as root
ERROR: but there is no HDFS_DATANODE_USER defined. Aborting operation.
Starting journal nodes [dn1 dn3 dn2]
ERROR: Attempting to operate on hdfs journalnode as root
ERROR: but there is no HDFS_JOURNALNODE_USER defined. Aborting operation.
Starting ZK Failover Controllers on NN hosts [nna nns]
ERROR: Attempting to operate on hdfs zkfc as root
ERROR: but there is no HDFS_ZKFC_USER defined. Aborting operation.
[root@nna hadoop-3.2.0]# jps
2175 NameNode
2527 Jps
[root@nna hadoop-3.2.0]#解决方法：
在Hadoop安装目录下找到sbin文件夹
在里面修改四个文件
1、对于start-dfs.sh和stop-dfs.sh文件，添加下列参数：
#!/usr/bin/env bash
HDFS_DATANODE_USER=root
HADOOP_SECURE_DN_USER=hdfs
HDFS_NAMENODE_USER=root
HDFS_SECONDARYNAMENODE_USER=root
2、对于start-yarn.sh和stop-yarn.sh文件，添加下列参数：
#!/usr/bin/env bash
YARN_RESOURCEMANAGER_USER=root
HADOOP_SECURE_DN_USER=yarn
YARN_NODEMANAGER_USER=root重新开始start...就可以。
参考链接：https://blog.csdn.net/hongxiao2016/article/details/88903289
