Viewing MapReduce job log files has been a pain. With YARN, you can enable the log aggregation. This will pull and aggregate all the individual logs belonging to a MR job and allow one to view the aggregated log with the following command.

You can view your MapReduce job log files using the following command

yarn logs -applicationId  <YOUR_APPLICATION_ID>  |less

eg.

yarn logs -applicationId  application_1399561129519_4422 |less

You can enable the log aggregation in the yarn-site.xml as follows

cat /etc/hadoop/conf/yarn-site.xml

<property>
<name>yarn.log-aggregation-enable</name>
<value>true</value>
</property>

To see the list of running MapReduce jobs

mapred job -list

To check the status of a MapReduce job

mapped job -status <YOUR_JOB_ID>