Hadoop环境CDH4.4
今天年后第一天上班（实习中），还过一个月，实习第一份实习合同就到期了~
Hadoop集群的虚拟环境看上去太乱，所以就将3个节点（1master + 2Slaves）重启，结果NodeManager启动失败。查看日志，记录错误如下：
2014-02-10 18:24:07,635 FATAL org.apache.hadoop.yarn.server.nodemanager.NodeManager: Error starting NodeManager
org.apache.hadoop.yarn.YarnException: Failed to Start org.apache.hadoop.yarn.server.nodemanager.NodeManager
at org.apache.hadoop.yarn.service.CompositeService.start(CompositeService.java:78)
at org.apache.hadoop.yarn.server.nodemanager.NodeManager.start(NodeManager.java:196)
at org.apache.hadoop.yarn.server.nodemanager.NodeManager.initAndStartNodeManager(NodeManager.java:329)
at org.apache.hadoop.yarn.server.nodemanager.NodeManager.main(NodeManager.java:351)
Caused by: org.apache.hadoop.yarn.YarnException: Failed to Start org.apache.hadoop.yarn.server.nodemanager.containermanager.ContainerManagerImpl
at org.apache.hadoop.yarn.service.CompositeService.start(CompositeService.java:78)
at org.apache.hadoop.yarn.server.nodemanager.containermanager.ContainerManagerImpl.start(ContainerManagerImpl.java:248)
at org.apache.hadoop.yarn.service.CompositeService.start(CompositeService.java:68)
... 3 more
Caused by: org.apache.hadoop.yarn.YarnException: Failed to check for existence of remoteLogDir [/var/log/hadoop-yarn/apps]
at org.apache.hadoop.yarn.server.nodemanager.containermanager.logaggregation.LogAggregationService.verifyAndCreateRemoteLogDir(LogAggregationService.java:179)
at org.apache.hadoop.yarn.server.nodemanager.containermanager.logaggregation.LogAggregationService.start(LogAggregationService.java:132)
at org.apache.hadoop.yarn.service.CompositeService.start(CompositeService.java:68)
... 5 more
2014-02-10 18:24:07,647 INFO org.apache.hadoop.ipc.Server: Stopping server on 52154
日志显示：无法启动NodeManager，无法启动ContainerManager（也就是没有分配资源容器管理进程），也无法检查远程日志目录（在HDFS上），原因锁定，无法与Master（具体来说是ResourceManager）通信，然后到master上查看防火墙是否关闭，Soga，果然防火墙是开着的，由于重启导致防火墙开启了，然后博主将Master上的防火墙关闭，并且chkconfig iptables off进行永久关闭（重启后不会自动开启），再去Slave节点上启动NodeManager，搞定！
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