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From "Roman Shaposhnik (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MAPREDUCE-3728) ShuffleHandler can't access results when configured in a secure mode
Date Wed, 25 Jan 2012 19:49:40 GMT
ShuffleHandler can't access results when configured in a secure mode

                 Key: MAPREDUCE-3728
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3728
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: mrv2, nodemanager
    Affects Versions: 0.23.0
            Reporter: Roman Shaposhnik
             Fix For: 0.23.1

While running the simplest of jobs (Pi) on MR2 in a fully secure configuration I have noticed
that the job was failing on the reduce side with the following messages littering the nodemanager

2012-01-19 08:35:32,544 ERROR org.apache.hadoop.mapred.ShuffleHandler: Shuffle error
org.apache.hadoop.util.DiskChecker$DiskErrorException: Could not find usercache/rvs/appcache/application_1326928483038_0001/output/attempt_1326928483038_0001_m_000003_0/file.out.index
in any of the configured local directories

While digging further I found out that the permissions on the files/dirs were prohibiting
nodemanager (running under the user yarn) to access these files:

$ ls -l /data/3/yarn/usercache/testuser/appcache/application_1327102703969_0001/output/attempt_1327102703969_0001_m_000001_0
-rw-r----- 1 testuser testuser 28 Jan 20 15:41 file.out
-rw-r----- 1 testuser testuser 32 Jan 20 15:41 file.out.index

Digging even further revealed that the group-sticky bit that was faithfully put on all the
subdirectories between testuser and application_1327102703969_0001 was gone from output and

Looking into how these subdirectories are created (org.apache.hadoop.yarn.server.nodemanager.containermanager.localizer.ContainerLocalizer.initDirs())
      // $x/usercache/$user/appcache/$appId/filecache
      Path appFileCacheDir = new Path(appBase, FILECACHE);
      appsFileCacheDirs[i] = appFileCacheDir.toString();
      lfs.mkdir(appFileCacheDir, null, false);
      // $x/usercache/$user/appcache/$appId/output
      lfs.mkdir(new Path(appBase, OUTPUTDIR), null, false);

Reveals that lfs.mkdir ends up manipulating permissions and thus clears sticky bit from output
and filecache.

At this point I'm at a loss about how this is supposed to work. My understanding was
that the whole sequence of events here was predicated on a sticky bit set so
that daemons running under the user yarn (default group yarn) can have access
to the resulting files and subdirectories down at output and below. Please let
me know if I'm missing something or whether this is just a bug that needs to be fixed.

On a related note, when the shuffle side of the Pi job failed the job itself didn't.
It went into the endless loop and only exited when it exhausted all the local storage
for the log files (at which point the nodemanager died and thus the job ended). Perhaps
this is even more serious side effect of this issue that needs to be investigated 

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