问题：因为ambari重启HDFS有某个节点失败导致，后续创建目录报错 根本原因：name node处于safe mode

错误信息：

Caused by: java.lang.RuntimeException: org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.ipc.RetriableException): org.apache.hadoop.hdfs.server.namenode.SafeModeException: Cannot create directory /tmp/hive/vagubchd/4ca66724-71ac-4d64-b263-3aca96514e8e. Name node is in safe mode.

解决方法：

检查

hdfs fsck /

#可以看到Minimally replicated blocks:   不为100%，可能缺少block
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2

关闭安全模式

hadoop dfsadmin -safemode leave
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修复

 hdfs fsck / | egrep -v '^\.+$' | grep -v eplica

参考

http://blog.csdn.net/hongweigg/article/details/7185328 
https://stackoverflow.com/questions/19205057/how-to-fix-corrupt-hdfs-files