1.namenode启动失败，查看错误原因，是无法格式化，再看日志，根据日志提示，清空对应的目录，即可解决这个问题。
2.datanode启动失败：
Can't open /var/run/cloudera-scm-agent/process/261-hdfs-DATANODE/supervisor.conf: Permission denied.
cd到/var/run/cloudera-scm-agent/process/261-hdfs-DATANODE目录下，看到：
-rw------- 1 root root 3146 2月 5 18:03 2018 supervisor.conf
怀疑是权限问题，上网查询了之后，才知道看起来是权限问题，其实不是，需要看看具体的datanode启动日志，于是到/var/log/hadoop-hdfs/目录下，清空目录，重新启动一下datanode，查看新生成的log日志，如下：
2018-02-05 18:29:10,370 WARN org.apache.hadoop.hdfs.server.common.Storage: java.io.IOException: Incompatible clusterIDs in /dfs/dn: namenode clusterID = cluster10; datanode
clusterID = cluster20
2018-02-05 18:29:10,371 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool <registering> (Datanode Uuid 5c80b393-7d62-4016-bafa-c44
63af7a45f) service to iot1/172.30.1.245:8022. Exiting.
java.io.IOException: All specified directories are failed to load.
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:478)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1394)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1355)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:317)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:228)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:829)
at java.lang.Thread.run(Thread.java:745)
2018-02-05 18:29:10,378 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool <registering> (Datanode Uuid 5c80b393-7d62-4016-bafa
-c4463af7a45f) service to iot1/172.30.1.245:8022
日志里有这样一行：
java.io.IOException: Incompatible clusterIDs in /dfs/dn: namenode clusterID = cluster10; datanode clusterID = cluster20
这就是namenode的clientID与datanode的clientID不一致的错误。
解决办法就是把datanode的clientID改的和namenode一致
datanode的clientID记录在/dfs/dn/current/VERSION文件中（即配置文件中dfs.data.dir在本地系统的路径的current/VERSION文件，dfs.data.dir这个目录可以在ClouderaManager的管理页面查找到）
最后修改的一致就解决问题了
# 打可执行jar包mvn package assembly:single
Can't open /var/run/cloudera-scm-agent/process/261-hdfs-DATANODE/supervisor.conf: Permission denied.
cd到/var/run/cloudera-scm-agent/process/261-hdfs-DATANODE目录下，看到：