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The tool tests if a scratch directory is in use, and if not, will remove it. This relies on HDFS write locks to detect if a scratch directory is in use. An HDFS client opens an HDFS file ($scratchdir/inuse.lck) for writing and only closes it at the time that the session is closed. cleardanglingscratchdir will try to open $scratchdir/inuse.lck for writing to test if the corresponding HiveCli/HiveServer2 is still running. If the lock is in use, the scratch directory will not be cleared. If the lock is available, the scratch directory will be cleared. Note that the NameNode only reclaims it might take NameNode up to 10 minutes to reclaim the lease on scratch file locks from a dead HiveCli/HiveServer2 after 10 minutes, at which point cleardanglingscratchdir will be able to remove it if run again.
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