在启动hadoop集群时发现其他进程都正常启动成功，唯独master主节点yarn的ResourceManager 进程没有启动成功，于是打开hadoop\logs下的日志查看resourcemanager 的日志文件，发现报错如下：
2021-04-30 09:51:02,103 FATAL org.apache.hadoop.yarn.server.resourcemanager.ResourceManager: Error starting ResourceManager
java.lang.NullPointerException
at org.apache.hadoop.yarn.server.api.protocolrecords.impl.pb.NodesToAttributesMappingRequestPBImpl.initNodeAttributesMapping(NodesToAttributesMappingRequestPBImpl.java:102)
at org.apache.hadoop.yarn.server.api.protocolrecords.impl.pb.NodesToAttributesMappingRequestPBImpl.getNodesToAttributes(NodesToAttributesMappingRequestPBImpl.java:117)
at org.apache.hadoop.yarn.nodelabels.store.op.FSNodeStoreLogOp.getNodeToAttributesMap(FSNodeStoreLogOp.java:46)
at org.apache.hadoop.yarn.nodelabels.store.op.NodeAttributeMirrorOp.recover(NodeAttributeMirrorOp.java:57)
at org.apache.hadoop.yarn.nodelabels.store.op.NodeAttributeMirrorOp.recover(NodeAttributeMirrorOp.java:35)
at org.apache.hadoop.yarn.nodelabels.store.AbstractFSNodeStore.loadFromMirror(AbstractFSNodeStore.java:120)
at org.apache.hadoop.yarn.nodelabels.store.AbstractFSNodeStore.recoverFromStore(AbstractFSNodeStore.java:149)
at org.apache.hadoop.yarn.server.resourcemanager.nodelabels.FileSystemNodeAttributeStore.recover(FileSystemNodeAttributeStore.java:95)
at org.apache.hadoop.yarn.server.resourcemanager.nodelabels.NodeAttributesManagerImpl.initNodeAttributeStore(NodeAttributesManagerImpl.java:140)
at org.apache.hadoop.yarn.server.resourcemanager.nodelabels.NodeAttributesManagerImpl.serviceStart(NodeAttributesManagerImpl.java:123)
at org.apache.hadoop.service.AbstractService.start(AbstractService.java:194)
at org.apache.hadoop.service.CompositeService.serviceStart(CompositeService.java:121)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager$RMActiveServices.serviceStart(ResourceManager.java:895)
at org.apache.hadoop.service.AbstractService.start(AbstractService.java:194)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.startActiveServices(ResourceManager.java:1262)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager$1.run(ResourceManager.java:1303)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager$1.run(ResourceManager.java:1299)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:422)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1730)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.transitionToActive(ResourceManager.java:1299)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.serviceStart(ResourceManager.java:1350)
at org.apache.hadoop.service.AbstractService.start(AbstractService.java:194)
at org.apache.hadoop.yarn.server.resourcemanager.ResourceManager.main(ResourceManager.java:1535)
2021-04-30 09:51:02,103 INFO org.apache.hadoop.ipc.Server: Stopping IPC Server Responder
出现的异常为空指针异常，解决办法就是进入/tmp目录，删除所以与yarn有关的目录：
#进入tmp cd /tmp #查看文件 ls #删除yarn所有相关目录(我这有hadoop用户和root用户都启动过，所以是两个) rm -rf /tmp/hadoop-yarn-hadoop rm -rf /tmp/hadoop-yarn-root
然后重启hadoop即可，如果还是不行，那就将hadoop hdfs重新格式化再去执行上面的操作。
