Develop Reference

Hadoop Installation and Running Taking Too Long in Windows 10

I successfully installed hadoop version 3.2.2 and have Java version 8 (JDK 1.8.0) and followed the tutorial here: https://www.youtube.com/watch?v=g7Qpnmi0Q-s
Here are my executions when running Hadoop in command prompt here:
The issue here is that hadoop (version 3.2.2) is taking way too long to load after successfully installing it in my local drive exactly like in the tutorial I followed above. I don't receive any errors or shutdown terminals after running start-dfs.cmd and start-yarn.cmd.
I can send how I set up my environment variables but I believe that I followed exactly that as described in the tutorial. Here is my setup:
Is there a solution to solve this issue?
I tried other StackOverflow posts but none of them specified how to tackle my issue with not loading Hadoop quickly. It actually never finishes loading even without errors or shutdowns.

grakn.ai installation error: Could not find or load main class ai.grakn.client.Client

I've recently installed and tried to use Grakn.ai for visualization. Following the instructions on grakn.ai's website, I ran into the following problem when trying to run:
\grakn-dist-0.15.0>.\bin\grakn.sh start
in Windows 10 command prompt, 64 bit, the following lines are displayed before exiting:
Starting redis
Cassandra already running
Starting engine.Error: Could not find or load main class
ai.grakn.engine.GraknEngineServer
Error: Could not find or load main class ai.grakn.client.Client
.Error: Could not find or load main class ai.grakn.client.Client
.Error: Could not find or load main class ai.grakn.client.Client
I have also attempted to add JAVA_HOME into System Variables, however this is to no avail. (I noticed that JAVA_HOME did not exist when I initially looked for it and so I had to manually create the variable and set jdk path - perhaps this implies some issue)
Thank you very much for your time and I'd be very grateful for any help.

You can start by checking the version of the jdk you are using. Grakn requires Oracle JDK 8 to be specific.
Also note, that Grakn does not yet officially support Windows because of Cassandra 2.1 being beta on windows. However you can get it working on windows. This page suggests how you can achieve it. I would recommend going with the docker version as it is simpler to work with.

Error: Could not find or load main class: running compiled JAR different errors depending on how I run it

PREFACE! I know similar questions have been asked a million times. I have read MANY hundreds of the previous questions and still cannot find my answer.
I am working on a raspberry pi and trying to run a Java application that is packaged in a Jar file. It was working fine before I installed the latest Java 1.8_111. I downgraded and it still didn't work. I then wiped my pi to defaults and it is still not working.
The current Java version is 1.8.0_65. I have decided that the java version is irrelevant by installing multiple different versions with the same result. When I installed a different version no other version was present to cause conflicts.
If I run the jar by simply doing java -jar KitchenScr.jar I get the following error:
Error: Could not find or load main class com.javafx.main.Main
If I run the jar from the supplied shell script(below). I get the following error.
Script
#!/bin/sh
DIRNAME=`dirname $0`
CP=$DIRNAME/KitchenScr.jar
# start uniCenta oPOS
java -cp $CP uk.chromis.kitchenscr.KitchenScr
Error
Error: Could not find or load main class uk.chromis.kitchenscr.KitchenScr
If I left anything out please let me know.

This was a simple issue that was staring me in the face.
Error: Could not find or load main class com.javafx.main.Main
Oracle stopped releasing JavaFX for ARM around Update 30 or something. It worked initially when I first bought my pi, but not after I installed a new OS because a newer version of Java was running.
Downgrade Java or add relevent ARM libraries for JavaFX.

mine worked. CP=$DIRNAME/KitchenScr.jar, I changed the capital letters of kitchenscr.jar to CP=$DIRNAME/kitchenscr.jar

CQLSH Protocol Error proceeding from apparent version conflicts

I am running Cassandra 3.7 on an Ubuntu Server 16.04 LTS 32bit machine that I'm re-purposing from storage. I managed to properly configure the JVM to operate within the 32 bit environment. Nodetool status works fine. But I am having a hard time getting CQLSH to work. I end up with the following error:
('Unable to connect to any servers', {'127.0.0.1': ProtocolError("cql_version '3.4.2' is not supported by remote (w/ native protocol). Supported versions: [u'3.4.0']",)})
Obviously there is some version conflict here but I'm confused as to why and how to fix it. I had a previous 3.0 install of Cassandra that I configured cassanda-env.sh to properly start the JVM. I kept that .sh file when I installed up to 3.7. I updated cassandra.yaml with the new install.
So my question here is: does Cassandra 3.7 support CQL 3.4.2? If not then why does it appear to ship with it? If it does not, what do I need to do to downgrade to CQL 3.4.0? If it does support it and my configuration files are wrong then what's the error and how do I fix it? Or, is there another configuration that I'm completely missing here?
Here are my current configurations:
cassandra-env.sh: https://www.dropbox.com/s/dcs99hgry5behqd/cassandra-env.sh?dl=0
cassandra.yaml:https://www.dropbox.com/s/boi8bh7gin0390f/cassandra.yaml?dl=0
Any assistance greatly appreciated.
EDIT: Figured out, with the help of the first answer, that I had an older instance of the server running. I couldn't get it to start with the correct version...so then I deleted cassandra from /etc/init.d and now I can't get the debian package to automatically register the service.
EDIT2: Downloaded cassandra script from git repo and now cassandra will start again after rebooting. Now cassandra -v shows me:
3.7
Which what I wanted to see and solved my issue pertaining to the version conflict. But now unfortunately I see a new error:
Connection error: ('Unable to connect to any servers', {'127.0.0.1': TypeError('ref() does not take keyword arguments',)})
This problem is addressed in: cqlsh connection error: 'ref() does not take keyword arguments'

It looks like you're running the 3.7 cqlsh against an older server instance. First, be sure you are actually running Cassandra 3.7 (you can probably just check the jar path or look in the logs).
If you want to connect using the advertised cql_version there is a command line option:
https://github.com/apache/cassandra/blob/cassandra-3.7/bin/cqlsh.py#L222
select release_version, cql_version from system.local;
(or just look at the cqlsh welcome header) to see what these parameters are.

Logstash Load Error

When I try to run logstash, I get a load error: JRuby ext built for wrong Java version. Does anyone know what this means and how I can resolve it. I`m running this on putty if it makes a difference.
Command Line Error

I had this error on a Windows box, and I solved it by updating Java.
In my case, I updated it from an earlier version of Java 8 to Java version "1.8.0_121".