一般由于多次格式化NameNode导致。在配置文件中保存的是第一次格式化时保存的namenode的ID，因此就会造成datanode与namenode之间的id不一致。
查看从节点机器hadoop中datanode的log文件 , 拉到最后 , 报错如下
然后找到datanode日志文件打开
2018-11-23 02:16:33,807 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: registered UNIX signal handlers for [TERM, HUP, INT]
2018-11-23 02:16:36,416 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
2018-11-23 02:16:36,881 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
2018-11-23 02:16:36,881 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: DataNode metrics system started
2018-11-23 02:16:36,935 INFO org.apache.hadoop.hdfs.server.datanode.BlockScanner: Initialized block scanner with targetBytesPerSec 1048576
2018-11-23 02:16:36,974 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Configured hostname is node1
2018-11-23 02:16:37,003 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Starting DataNode with maxLockedMemory = 0
2018-11-23 02:16:37,171 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Opened streaming server at /0.0.0.0:50010
2018-11-23 02:16:37,174 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Balancing bandwith is 1048576 bytes/s
2018-11-23 02:16:37,175 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Number threads for balancing is 5
2018-11-23 02:16:37,790 INFO org.mortbay.log: Logging to org.slf4j.impl.Log4jLoggerAdapter(org.mortbay.log) via org.mortbay.log.Slf4jLog
2018-11-23 02:16:37,834 INFO org.apache.hadoop.security.authentication.server.AuthenticationFilter: Unable to initialize FileSignerSecretProvider, falling back to use random secrets.
2018-11-23 02:16:37,871 INFO org.apache.hadoop.http.HttpRequestLog: Http request log for http.requests.datanode is not defined
2018-11-23 02:16:37,914 INFO org.apache.hadoop.http.HttpServer2: Added global filter 'safety' (class=org.apache.hadoop.http.HttpServer2$QuotingInputFilter)
2018-11-23 02:16:37,917 INFO org.apache.hadoop.http.HttpServer2: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context datanode
2018-11-23 02:16:37,917 INFO org.apache.hadoop.http.HttpServer2: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context static
2018-11-23 02:16:37,918 INFO org.apache.hadoop.http.HttpServer2: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context logs
2018-11-23 02:16:38,084 INFO org.apache.hadoop.http.HttpServer2: Jetty bound to port 43865
2018-11-23 02:16:38,084 INFO org.mortbay.log: jetty-6.1.26
2018-11-23 02:16:39,757 INFO org.mortbay.log: Started HttpServer2$SelectChannelConnectorWithSafeStartup@localhost:43865
2018-11-23 02:16:40,913 INFO org.apache.hadoop.hdfs.server.datanode.web.DatanodeHttpServer: Listening HTTP traffic on /0.0.0.0:50075
2018-11-23 02:16:42,063 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: dnUserName = root
2018-11-23 02:16:42,063 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: supergroup = supergroup
2018-11-23 02:16:42,374 INFO org.apache.hadoop.ipc.CallQueueManager: Using callQueue class java.util.concurrent.LinkedBlockingQueue
2018-11-23 02:16:42,494 INFO org.apache.hadoop.ipc.Server: Starting Socket Reader #1 for port 50020
2018-11-23 02:16:42,554 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Opened IPC server at /0.0.0.0:50020
2018-11-23 02:16:42,579 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Refresh request received for nameservices: null
2018-11-23 02:16:42,613 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Starting BPOfferServices for nameservices: <default>
2018-11-23 02:16:42,645 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool <registering> (Datanode Uuid unassigned) service to node1/127.0.0.1:9000 starting to offer service
2018-11-23 02:16:42,666 INFO org.apache.hadoop.ipc.Server: IPC Server Responder: starting
2018-11-23 02:16:42,668 INFO org.apache.hadoop.ipc.Server: IPC Server listener on 50020: starting
2018-11-23 02:16:43,745 INFO org.apache.hadoop.hdfs.server.common.Storage: Using 1 threads to upgrade data directories (dfs.datanode.parallel.volumes.load.threads.num=1, dataDirs=1)
2018-11-23 02:16:43,776 INFO org.apache.hadoop.hdfs.server.common.Storage: Lock on /var/data/hadoop/dfs/data/in_use.lock acquired by nodename 3212@node1
2018-11-23 02:16:43,781 WARN org.apache.hadoop.hdfs.server.common.Storage: Failed to add storage directory [DISK]file:/var/data/hadoop/dfs/data/
java.io.IOException: Incompatible clusterIDs in /var/data/hadoop/dfs/data: namenode clusterID = CID-a9130806-4b28-4a93-92b0-41f04d17ca07; datanode clusterID = CID-1435a0cf-33c1-4c5e-9473-b88769f60dcd
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:775)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.loadStorageDirectory(DataStorage.java:300)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.loadDataStorage(DataStorage.java:416)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.addStorageLocations(DataStorage.java:395)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:573)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1362)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1327)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:317)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:223)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:802)
at java.lang.Thread.run(Thread.java:745)
2018-11-23 02:16:43,789 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool <registering> (Datanode Uuid unassigned) service to node1/127.0.0.1:9000. Exiting.
java.io.IOException: All specified directories are failed to load.
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:574)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1362)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1327)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:317)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:223)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:802)
at java.lang.Thread.run(Thread.java:745)
2018-11-23 02:16:43,790 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool <registering> (Datanode Uuid unassigned) service to node1/127.0.0.1:9000
2018-11-23 02:16:43,898 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Removed Block pool <registering> (Datanode Uuid unassigned)
2018-11-23 02:16:45,899 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
2018-11-23 02:16:45,901 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 0
2018-11-23 02:16:45,904 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down DataNode at node1/127.0.0.1
************************************************************/
如图，复制这个namenode clusterID。
找到data目录，在这个目录下，有一个VERSION文件。将VERSION中的clusterID改成上面复制的ID。
找到current 中的VERSION 打开
/var/data/hadoop/dfs/data/current
复制修改clusterID
保存
重启服务
DataNode已经出现了