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From Chris Nauroth <cnaur...@hortonworks.com>
Subject Re: simple hadoop MR program to be executed using java
Date Fri, 16 Jan 2015 19:03:59 GMT
Hello Rab,

There is actually quite a lot of logic in the "hadoop jar" shell scripts to
set up the classpath (including Hadoop configuration file locations) and
set up extra arguments (like heap sizes and log file locations).  It is
possible to replicate it with a straight java call, but it might not be
worth the effort, and end users of your jar would lose functionality
implemented in the shell scripts, such as configuration file location
overrides.

If you still want to pursue this, then you might want to make a small
change to the "hadoop jar" script and add a line right before the java call
to echo the command it's running.  That will give you a sense for the java
command that ultimately gets run.  You could also take a look at the
process table for a running "hadoop jar" process and inspect its command
line and environment variables.

Another potentially helpful tool  is the "hadoop classpath" command:

http://hadoop.apache.org/docs/r2.6.0/hadoop-project-dist/hadoop-common/CommandsManual.html#classpath

This uses the full logic of the shell scripts for classpath construction,
but then just echoes it instead of using it to run a jar.

Chris Nauroth
Hortonworks
http://hortonworks.com/


On Fri, Jan 16, 2015 at 10:15 AM, rab ra <rabmdu@gmail.com> wrote:

> Hello,
>
> I have a simple java program that sets up a MR job. I could successfully
> execute this in Hadoop infrastructure (hadoop 2x) using 'hadoop jar
> <myjar>'. But I want to achieve the same thing using java command as below.
>
> java <className>
>
> 1. How can I pass hadoop configuration to this className?
> 2. What extra arguments do I need to supply?
> 3. Any link/documentation would be highly appreciated.
>
>
> regards
> rab
>
>
>

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