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From "Vinod Kumar Vavilapalli (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8731) Public distributed cache support for Windows
Date Tue, 25 Sep 2012 00:44:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13462302#comment-13462302

Vinod Kumar Vavilapalli commented on HADOOP-8731:

Tx for the reiteration, Bikas.

Ivan to clarify, this is how it works:
 - JobClient is given a URI: it could be a local file:// URI or one on hdfs:///
 - JobClient sees if the path is on the same FS as JobTracker's and if not, it copies it.
So if you passed a file:///tmp/a.jar to -libjars/-files/-archives, JobClient will copy it
into user's jobSubmitDir.
 - So for file:/// paths, the visibility checks are not made. Only in your test-case scenario,
where FS = LocalFS, these checks will be made. Hence my comment.
> Public distributed cache support for Windows
> --------------------------------------------
>                 Key: HADOOP-8731
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8731
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: filecache
>            Reporter: Ivan Mitic
>            Assignee: Ivan Mitic
>         Attachments: HADOOP-8731-PublicCache.patch
> A distributed cache file is considered public (sharable between MR jobs) if OTHER has
read permissions on the file and +x permissions all the way up in the folder hierarchy. By
default, Windows permissions are mapped to "700" all the way up to the drive letter, and it
is unreasonable to ask users to change the permission on the whole drive to make the file
public. IOW, it is hardly possible to have public distributed cache on Windows. 
> To enable the scenario and make it more "Windows friendly", the criteria on when a file
is considered public should be relaxed. One proposal is to check whether the user has given
EVERYONE group permission on the file only (and discard the +x check on parent folders).
> Security considerations for the proposal: Default permissions on Unix platforms are usually
"775" or "755" meaning that OTHER users can read and list folders by default. What this also
means is that Hadoop users have to explicitly make the files private in order to make them
private in the cluster (please correct me if this is not the case in real life!). On Windows,
default permissions are "700". This means that by default all files are private. In the new
model, if users want to make them public, they have to explicitly add EVERYONE group permissions
on the file. 
> TestTrackerDistributedCacheManager fails because of this issue.

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