FAQs

Last updated: June 12th, 2019

Cluster Operations with Hadoop

How many instances can I create on my cluster?

The number of instances depends on the amount of hardware resources that are present on your PC, laptop or Mac. We were able to run one master and six slaves (7 instances) on a Mac with 4 GB and 2 CPUs allocated to Docker. The rest depends on the Hadoop configuration for its services as a MapReduce job requesting a lot of resources will be failing. It is recommended to run Yarn applications if your machine can spare more resources than the given example.

Why is Hadoop's replication factor on Hadjo 1 by default?

By default at Hadjo "hdfs-site.xml" has the property "dfs.replication" set to "1" due to the expected lack of resources of a single PC. One can always change this by going to "Settings/Cluster Software" then click on the Hadoop version icon. Locate the file "hdfs-site.xml", correct, save and create a new image build.

What are the Hadoop settings that my cluster runs with?

One can always see and change Hadoop related settings by going to "Settings/Cluster Software" and click on the configuration icon on the right of Hadoop version (your selected version for your cluster). Then the configuration files of your selected Hadoop version are available for you. Please not that some properties, ex. "${mount_dir_replace}", are dynamically set during a Docker image build and it is not advised to edited these ones! If configuration changes are applied a new build id required.

I messed some Hadoop configurations and want to reset. How?

One can always reset to the default Hadjo Hadoop settings by going to "Settings/Cluster Software" and click on the "reset" icon, the rightest one of the selected Hadoop version row. A new Docker image build is required and you are all set.

Port binding with permission denied error on cluster start.

An error having a similar content "Error starting userland proxy: Bind for 0.0.0.0:50070: unexpected error Permission denied" indicates that a port(for ex. 50070) has been reserved by your own OS. Such ports are usually reserved by some application of your OS with a "start" and "end" range.

Windows

Hadjo Windows installer gives "Access Denied" error. Why?

Hadjo does not require any specific install location. Usually "Access Denied" error happens if the install directory of choice is "C:\Program Files\" or one that the current user has no write access to. In that case the installer must be run as administrator user. The application itself does not require to be installed at a special folder or any administrator privileges to run.

Windows SmartFilter shows "Unknown Published" during my install attempt. Why is that and what can I do?

Hadjo EXE installer has been signed by a code signing certificate issued by Apple Inc.. There have been many debates why Microsoft does not put Apple in their chain of trust, anyway. One can check the certificate by right-clicking the EXE and see the "Digital Signatures" tab. The recommended option which does not need installation and does not make Windows complain is using the portable ZIP version of Hadjo.

Linux

Using Hadjo on my Linux gives me access denied errors. Why ?

This case usually happens when one has forgotten to add his user (the one that runs Hadjo application) to "docker" group as specified under the Docker install requirements.

Using Hadjo on my Linux gives me "Could not find or load main class". Why ? New

An error of type "Error: Could not find or load main class com.lazyweaver.hadjo.MainApp Caused by: java.lang.NoClassDefFoundError: javafx/application/Application" is observed when the OS has installed OpenJDK. The JavaFX project (used by Hadjo) itself is open source and is part of the OpenJDK project. You can easily add it to Linux by sudo apt-get install openjfx.
You can always install Hadjo with bundled JRE.

Hadjo on my Linux is installed but does not start at all. Why ? New

This issue is observed when the OS has installed OpenJDK and Hadjo is installed from package without JRE bundle (or all-platform ZIP). The JavaFX project (used by Hadjo) itself is open source and is part of the OpenJDK project. You can easily add it to Linux by sudo apt-get install openjfx
You can always install Hadjo with bundled JRE.

MacOS

Hadjo on my Mac is installed but does not start at all. Why ? New

This issue is observed when the OS has installed OpenJDK and Hadjo is installed from package without JRE bundle (or all-platform ZIP). The JavaFX project (used by Hadjo) itself is open source and is part of the OpenJDK project. You can add it to MacOS by checking here
You can always install Hadjo with bundled JRE.

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