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From Chris Nauroth <cnaur...@hortonworks.com>
Subject Re: Bulk chmod,chown operations on HDFS
Date Thu, 16 Jun 2016 05:54:20 GMT
Hello Ravi,

You might consider using DistCh.  In the same way that DistCp is a distributed copy implemented
as a MapReduce job, DistCh is a MapReduce job that distributes the work of chmod/chown.

DistCh will become easier to access through convenient shell commands in Apache Hadoop 3.
 In version 2.6.0, it's undocumented and hard to find, but it's still there.  It's inside
the hadoop-extras.jar.  Here is an example invocation:

hadoop jar share/hadoop/tools/lib/hadoop-extras-*.jar org.apache.hadoop.tools.DistCh

It might take some fiddling with the classpath to get this right.  If so, then I recommend
looking at how the shell scripts in trunk set up the classpath.


As you pointed out, this would generate higher NameNode traffic compared to your typical baseline
load.  To mitigate this, I recommend that you start with a test run in a non-production environment
to see how it reacts.

--Chris Nauroth

From: ravi teja <raviorteja@gmail.com<mailto:raviorteja@gmail.com>>
Date: Wednesday, June 15, 2016 at 8:33 PM
To: "user@hadoop.apache.org<mailto:user@hadoop.apache.org>" <user@hadoop.apache.org<mailto:user@hadoop.apache.org>>
Subject: Bulk chmod,chown operations on HDFS

Hi Community,

As part of the new authorisation changes, we need to change the permissions and owners of
many files in hdfs (2.6.0) with chmod and chown.

To do this we need to stop the processing on the directories to avoid inconsistencies in permissions,
hence we need to take a downtime for those specific pipelines operating on these folders.

The total number of files/directories to be operated upon is around 10 Million.
A chmod recursive (chmod -R) on 160K objects, has taken around 15 minutes.

At this rate it will take a long time to complete the operation and the downtime would be
couple of hours.

Mapreduce program  is one option, but chmod,chown being a heavy operations, will slow down
the cluster for other users, if done at this scale.

Are there any options to do a bulk permissions changes chmod,chown to avoid these issues?
If not are there any alternative approaches to carry the same operation at this scale something
like admin backdoor to fsimage?

Ravi Teja

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