Check out example codes for "WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable". It will help you in understanding the concepts better.

Code Example 1

Sounds silly, but if you've copied .bashrc lines from somewhere
check that the quotation marks are like this:
    export HADOOP_OPTS="-Djava.library.path=$HADOOP_HOME/lib/native"
and not like this
    export HADOOP_OPTS=”-Djava.library.path=$HADOOP_HOME/lib/native”

...took me some time

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