core-site.xml

Describes the core-site.xml file that contains the configuration that overrides the default core parameters.

The /opt/mapr/hadoop/hadoop-2.x.x/etc/hadoop/core-site.xml file contains configuration that override the default core parameters.
NOTE
/opt/mapr/hadoop/hadoop-0.20.2/conf/core-site.xml is a symlink to /opt/mapr/hadoop/hadoop-2.x/etc/hadoop/core-site.xml.

To override a default value, specify the new value within the <configuration> tags, using the following format:

<property>
  <name> </name>
  <value> </value>
  <description> </description>
</property>

Default core Parameters describes the possible entries to place in the <name> and <value> tags. The <description> tag is optional but recommended for maintainability.

WARNING
You can examine the current configuration information for this node by using the hadoop conf -dump command from a command line.
Default core-site.xml file 
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

<!-- Put site-specific property overrides in this file. -->

<configuration>

</configuration>

Core Parameters

See Default core Parameters.