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https://issues.apache.org/jira/browse/MAPREDUCE-1595?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844452#action_12844452
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Vinod K V commented on MAPREDUCE-1595:
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Consider this failure case:
 - Two mapred-local-dirs "/a/b/c/ML1" and "/a/b/c/ML2".
 - TT first creates userdir Alice in both the dirs, i.e. 
"/a/b/c/ML1/taskTracker/Alice" and "/a/b/c/ML2/taskTracker/Alice"
 - TT then launched LinuxTaskController for 'securifying' the user-dirs aka 
MAPREDUCE-856.
 - LinuxTaskController then successfully changes ownership of 
"/a/b/c/ML1/taskTracker/Alice" to "Alice:tt_group" but then fails on changing 
ownership of "/a/b/c/ML2/taskTracker/Alice" due to a transitory disk problem.

The above result in the failure of current task because of a failed 
INITIALIZE_USER operation.
Not just that, every other task of Alice that ever comes on this TT will try 
INITIALIZE_USER and fail because LinuxTaskController see "Alice:tt_group" on 
"/a/b/c/ML1/taskTracker/Alice" and fails saying the file is not owned by TT.

This can otherwise only be rectified when TT restarts/reinits and moves and 
deletes the old mapred-local-dirs.

> LinuxTaskController is too strict on the initial ownership of files/dir.
> ------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-1595
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1595
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: security, task-controller
>            Reporter: Vinod K V
>             Fix For: 0.22.0
>
>
> Linux task controller is too strict now w.r.t the initial ownership of the 
> files/dir that it tries to make as secure as possible. Currently, it expects, 
> for e.g, the mapred-local/tasktracker/user-dir to be both user-owned and 
> group-owned by TT. This leads to unrecoverable failures in some corner cases.
> It can instead allow the files/dirs to be owned either by TT *or* by the 
> jobOwner.

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