1 如果机群时间不同步，那么启动子节点RegionServer就会出问题
aused by: org.apache.hadoop.hbase.ipc.RemoteWithExtrasException(org.apache.hadoop.hbase.ClockOutOfSyncException): org.apache.hadoop.hbase.ClockOutOfSyncException:
Server slave1,, has been rejected; Reported time is too far out of sync with master. Time difference of 43201045ms > max allowed of 180000ms
解决办法，同步集群时间，可参考http://www.cnblogs.com/liuchangchun/p/4685032.html
2 HMaster启动失败，报如下错误
2015-08-27 22:10:42,079 FATAL [spark-1421-0002:16020.activeMasterManager] master.HMaster: Failed to become active master
org.apache.hadoop.hbase.TableExistsException: hbase:namespace
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.checkAndSetEnablingTable(CreateTableHandler.java:151)
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.prepare(CreateTableHandler.java:124)
at org.apache.hadoop.hbase.master.TableNamespaceManager.createNamespaceTable(TableNamespaceManager.java:233)
at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:86)
at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:868)
at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:719)
at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:165)
at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1425)
at java.lang.Thread.run(Thread.java:745)
2015-08-27 22:10:42,080 FATAL [spark-1421-0002:16020.activeMasterManager] master.HMaster: Master server abort: loaded coprocessors are: []
2015-08-27 22:10:42,080 FATAL [spark-1421-0002:16020.activeMasterManager] master.HMaster: Unhandled exception. Starting shutdown.
org.apache.hadoop.hbase.TableExistsException: hbase:namespace
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.checkAndSetEnablingTable(CreateTableHandler.java:151)
at org.apache.hadoop.hbase.master.handler.CreateTableHandler.prepare(CreateTableHandler.java:124)
at org.apache.hadoop.hbase.master.TableNamespaceManager.createNamespaceTable(TableNamespaceManager.java:233)
at org.apache.hadoop.hbase.master.TableNamespaceManager.start(TableNamespaceManager.java:86)
at org.apache.hadoop.hbase.master.HMaster.initNamespace(HMaster.java:868)
at org.apache.hadoop.hbase.master.HMaster.finishActiveMasterInitialization(HMaster.java:719)
at org.apache.hadoop.hbase.master.HMaster.access$500(HMaster.java:165)
at org.apache.hadoop.hbase.master.HMaster$1.run(HMaster.java:1425)
at java.lang.Thread.run(Thread.java:745)
解决办法：
2.1 停掉HBase服务
2.2 执行如下命令，修复HBase元数据
hbase org.apache.hadoop.hbase.util.hbck.OfflineMetaRepair
2.3 删掉zookeeper中的数据
hbase zkcli
rmr /hbase
2.4 完成之后输入quit退出
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参考：
http://*.com/questions/28563167/hbase-master-not-starting-correctly
http://*.com/questions/24333183/hbase-master-keeps-dying-claims-a-hbasenamespace-already-exists
https://community.cloudera.com/t5/Storage-Random-Access-HDFS/HMaster-not-starting-TableExistsException/td-p/11466
http://www.cnblogs.com/zemliu/p/3824629.html