MAPREDUCE-6149. Document override log4j.properties in MR job. Contributed by Junping Du.

hadoop-mapreduce-project/CHANGES.txt

@@ -238,6 +238,9 @@ Release 2.7.0 - UNRELEASED
 
   IMPROVEMENTS
 
+    MAPREDUCE-6149. Document override log4j.properties in MR job.
+    (Junping Du via harsh)
+
     MAPREDUCE-6194. Bubble up final exception in failures during creation
     of output collectors (Varun Saxena via harsh)
 

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/resources/mapred-default.xml

@@ -324,6 +324,8 @@
   <value>INFO</value>
   <description>The logging level for the map task. The allowed levels are:
   OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE and ALL.
+  The setting here could be overridden if "mapreduce.job.log4j-properties-file"
+  is set.
   </description>
 </property>
 
@@ -332,6 +334,8 @@
   <value>INFO</value>
   <description>The logging level for the reduce task. The allowed levels are:
   OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE and ALL.
+  The setting here could be overridden if "mapreduce.job.log4j-properties-file"
+  is set.
   </description>
 </property>
 
@@ -1163,6 +1167,17 @@
   </description>
 </property>
 
+  <property>
+    <name>mapreduce.job.log4j-properties-file</name>
+    <value></value>
+    <description>Used to override the default settings of log4j in container-log4j.properties
+    for NodeManager. Like container-log4j.properties, it requires certain
+    framework appenders properly defined in this overriden file. The file on the
+    path will be added to distributed cache and classpath. If no-scheme is given
+    in the path, it defaults to point to a log4j file on the local FS.
+    </description>
+  </property>
+
 <property>
   <name>mapreduce.job.end-notification.max.retry.interval</name>
   <value>5000</value>