寫在最前注意：
1、master，slave都需要修改start-dfs.sh，stop-dfs.sh，start-yarn.sh，stop-yarn.sh四個文件
2、如果你的Hadoop是另外啓用其它用戶來啓動，記得將root改爲對應用戶
HDFS格式化後啓動dfs出現以下錯誤：
[root@master sbin]# ./start-dfs.sh
Starting namenodes on [master]
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.
查度娘，見一仁兄的博客有次FAQ，故參考處理順便再做一記錄
參考地址：https://blog.csdn.net/u013725455/article/details/70147331
在/hadoop/sbin路徑下：
將start-dfs.sh，stop-dfs.sh兩個文件頂部添加以下參數
#!/usr/bin/env bash
HDFS_DATANODE_USER=root
HADOOP_SECURE_DN_USER=hdfs
HDFS_NAMENODE_USER=root
HDFS_SECONDARYNAMENODE_USER=root
還有，start-yarn.sh，stop-yarn.sh頂部也需添加以下：
#!/usr/bin/env bash
YARN_RESOURCEMANAGER_USER=root
HADOOP_SECURE_DN_USER=yarn
YARN_NODEMANAGER_USER=root
修改後重啓 ./start-dfs.sh，成功！
[root@master sbin]# ./start-dfs.sh
WARNING: HADOOP_SECURE_DN_USER has been replaced by HDFS_DATANODE_SECURE_USER. Using value of HADOOP_SECURE_DN_USER.
Starting namenodes on [master]
上一次登錄：日 6月 3 03:01:37 CST 2018從 slave1pts/2 上
master: Warning: Permanently added 'master,192.168.43.161' (ECDSA) to the list of known hosts.
Starting datanodes
上一次登錄：日 6月 3 04:09:05 CST 2018pts/1 上
Starting secondary namenodes [slave1]
上一次登錄：日 6月 3 04:09:08 CST 2018pts/1 上