在以root用户启动hadoop集群时遇到了下面这个问题，看报错信息是用户问题，

[root@hadoop10 hadoop-3.1.3]# sbin/start-dfs.sh 
Starting namenodes on [hadoop10]
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 [hadoop12]
ERROR: Attempting to operate on hdfs secondarynamenode as root
ERROR: but there is no HDFS_SECONDARYNAMENODE_USER defined. Aborting operation.

解决方法：

在环境变量中添加配置

vim /etc/profile.d/my_env.sh

* my_env.sh是自己添加的文件，不建议直接修改profile.d

添加的配置如下：

export HDFS_NAMENODE_USER=root
export HDFS_DATANODE_USER=root
export HDFS_SECONDARYNAMENODE_USER=root
export YARN_RESOURCEMANAGER_USER=root
export YARN_NODEMANAGER_USER=root

修改完成后，需要执行以下命令立即生效

source /etc/profile.d/my_env.sh