This page describes how to get your environment setup and is IDE agnostic.

Requirements

• Java 6
• Ant
• Junit
• Your favorite IDE

Setup Your Development Environment in Linux

The instructions below talk about how to get an environment setup using the command line to build, control source, and test. These instructions are therefore IDE independent. Take a look at EclipseEnvironment for instructions on how to configure Eclipse to build, control source, and test. If you prefer ItelliJ IDEA, then take a look here

• Choose a good place to put your code. You will eventually use your source code to run Hadoop, so choose wisely. I chose /code/hadoop.

• Get the source. This is documented here: HowToContribute. Put the source in /code/hadoop (or whatever you chose) so that you have /code/hadoop/hadoop-core-trunk

• cd into hadoop-core-trunk, or whatever you named the directory

• attempt to run ant test

  • If you get any strange errors (other than JUnit test failures and errors), then consult the Build Errors section below.

• run ant to compile (this may not be necessary if you've already run ant test)

• follow GettingStartedWithHadoop to learn how to run Hadoop (use this guide if you use Ubuntu: http://wiki.apache.org/hadoop/Running_Hadoop_On_Ubuntu_Linux_%28Single-Node_Cluster%29)

  • Use the hadoop-core-trunk folder just as you would a downloaded version of Hadoop (symlink hadoop-core-trunk to hadoop)

  • If you run in to any problems, refer to the Runtime Errors below, along with the troubleshooting document here: TroubleShooting

Build Errors

/code/hadoop-core-trunk/build.xml:634: Could not create task or type of type: junit.

Refer to the following site: http://ant.apache.org/manual/OptionalTasks/junit.html

My default install of ant was missing ant-junit.jar in ANT_HOME/lib (for me, /usr/share/ant/lib), so I downloaded ant manually to get the jar. Make sure you download the same version of ant that as the version that is preinstalled! To check the version of ant that you have, run ant -version.

Runtime Errors

ERROR dfs.NameNode: java.io.IOException: javax.security.auth.login.LoginException: Login failed: id: cannot find name for group ID

This was a specific error that I received that probably no one else will receive. The error has to do with a permission issue when running Hadoop. At runtime, Hadoop SSHes into all nodes, including itself in a single-node setup. This error occurred because some LDAP groups that I belonged to were not found at Hadoop runtime. If you get an error like this, then there can be a number of things wrong, but very generally you have a permissions error. The following guide may help if you're running Ubuntu: http://wiki.apache.org/hadoop/Running_Hadoop_On_Ubuntu_Linux_%28Single-Node_Cluster%29

could only be replicated to 0 nodes, instead of 1

I was getting this error when putting data into the dfs. The solution is strange and probably inconsistent: I erased all temporary data along with the namenode, reformatted the namenode, started everything up, and visited my "cluster's" dfs health page (http://your_host:50070/dfshealth.jsp). The last step, visiting the health page, is the only way I can get around the error. Once I've visited the page, putting and getting files in and out of the dfs works great!

DataNode process appearing then disappearing on slave

When transitioning from a single-node cluster to a multi-node cluster, one of your nodes may appear to be up at first and then will go down immediately. Check the datanode logs of the node that goes down, and look for a connection refused error. If you get this connection refused error, then this means that your slave is having difficulties finding the master. I did two things to solve this problem, and I'm not sure which one, if not both, solved it. First, erase all of your hadoop temporary data and the namenode on all masters and slaves. Reformat the namenode. Second, make sure all of your master and slave hosts in the conf files (slaves, masters, hadoop-site.xml) refer to full host names (ex: host.domain.com instead of host).