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 secondary namenodes [slave1]

        ERROR: Attempting to operate on hdfs secondarynamenode as root

        ERROR: but there is no HDFS_SECONDARYNAMENODE_USER defined. Aborting operation.

二、解决办法

在/hadoop/sbin路径下： 

将start-dfs.sh，stop-dfs.sh两个文件顶部添加以下参数

HDFS_DATANODE_USER=root
HDFS_DATANODE_SECURE_USER=hdfs
HDFS_NAMENODE_USER=root
HDFS_SECONDARYNAMENODE_USER=root

如下图：

start-yarn.sh，stop-yarn.sh顶部也添加以下参数
YARN_RESOURCEMANAGER_USER=root
HADOOP_SECURE_DN_USER=yarn
YARN_NODEMANAGER_USER=root

 如下图：

三、添加完启动遇到如下警告：

WARNING: HADOOP_SECURE_DN_USER has been replaced by HDFS_DATANODE_SECURE_USER.

需要将第二句：HADOOP_SECURE_DN_USER=hdfs  改为 HDFS_DATANODE_SECURE_USER=hdfs