When executing the official documentation installation guide, enter the command:
sbin/start-dfs.sh
Error: there is no HDFS_NAMENODE_USER defined. Aborting operation.

According to the error message, we found that HDFS_NAMENODE_USER and HDFS_DATANODE_USER are not defined

Solution:
Add the following codes in sbin/start-dfs:

HDFS_DATANODE_USER=root
HADOOP_SECURE_DN_USER=hdfs
HDFS_NAMENODE_USER=root
HDFS_SECONDARYNAMENODE_USER=root