一段时间后，重新启动hadoop之后，没有显示应有的五个进程。一般情况下从logs目录出发，进行修改。最经常报的错误是：
1. 端口绑定失败
这种情况下一般是端口占用，执行命令netstat -anp |grep 端口号,查看占用该端口的进程，并执行kill 9 进程号，再次重启即可。
2. datanode报错信息如下
2019-04-10 20:06:07,948 WARN org.apache.hadoop.hdfs.server.common.Storage: Failed to add storage directory [DISK]file:/root/hadoop/dfs/data/
java.io.IOException: Incompatible clusterIDs in /root/hadoop/dfs/data: namenode clusterID = CID-deb400ff-00be-4e84-b647-6be4edbe6abb; datanode clusterID = CID-83f6523b-7765-4eb1-abde-5887636778c9
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:760)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.loadStorageDirectory(DataStorage.java:293)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.loadDataStorage(DataStorage.java:409)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.addStorageLocations(DataStorage.java:388)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:556)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1574)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1535)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:382)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:266)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:750)
at java.lang.Thread.run(Thread.java:748)
2019-04-10 20:06:07,950 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool ID needed, but service not yet registered with NN, trace:
java.lang.Exception
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.getBlockPoolId(BPOfferService.java:210)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.hasBlockPoolId(BPOfferService.java:220)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.shouldRetryInit(BPOfferService.java:826)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.shouldRetryInit(BPServiceActor.java:792)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:755)
at java.lang.Thread.run(Thread.java:748)
2019-04-10 20:06:07,950 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool <registering> (Datanode Uuid 360e4398-6fcd-409e-bab7-15207af21561) service to test01/172.17.15.27:9000. Exiting.
java.io.IOException: All specified directories are failed to load.
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:557)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1574)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1535)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:382)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:266)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:750)
at java.lang.Thread.run(Thread.java:748)
2019-04-10 20:06:07,951 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool <registering> (Datanode Uuid 360e4398-6fcd-409e-bab7-15207af21561) service to test01/172.17.15.27:9000
2019-04-10 20:06:08,061 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool ID needed, but service not yet registered with NN, trace:
java.lang.Exception
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.getBlockPoolId(BPOfferService.java:210)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.hasBlockPoolId(BPOfferService.java:220)
at org.apache.hadoop.hdfs.server.datanode.BlockPoolManager.remove(BlockPoolManager.java:90)
at org.apache.hadoop.hdfs.server.datanode.DataNode.shutdownBlockPool(DataNode.java:1490)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.shutdownActor(BPOfferService.java:465)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.cleanUp(BPServiceActor.java:527)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:787)
at java.lang.Thread.run(Thread.java:748)
2019-04-10 20:06:08,061 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Removed Block pool <registering> (Datanode Uuid 360e4398-6fcd-409e-bab7-15207af21561)
2019-04-10 20:06:08,061 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool ID needed, but service not yet registered with NN, trace:
java.lang.Exception
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.getBlockPoolId(BPOfferService.java:210)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.hasBlockPoolId(BPOfferService.java:220)
at org.apache.hadoop.hdfs.server.datanode.DataNode.shutdownBlockPool(DataNode.java:1491)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.shutdownActor(BPOfferService.java:465)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.cleanUp(BPServiceActor.java:527)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:787)
at java.lang.Thread.run(Thread.java:748)
2019-04-10 20:06:10,074 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
2019-04-10 20:06:10,076 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 0
2019-04-10 20:06:10,129 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
根据报错信息java.io.IOException: Incompatible clusterIDs in /root/hadoop/dfs/data: namenode clusterID = CID-deb400ff-00be-4e84-b647-6be4edbe6abb; datanode clusterID = CID-83f6523b-7765-4eb1-abde-5887636778c9和博客可知，namenode和datanode的clusterID不同造成的解决办法:
根据日志中的路径，cd /root/hadoop/dfs/下面有data和name两个文件夹，
将/root/hadoop/dfs/name/current下的VERSION中的clusterID覆盖掉/root/hadoop/dfs/data/current下的VERSION的clusterID即可。
全部修改完毕后，重启即可。
Hadoop成功启动
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