How Do You Troubleshoot the Hadoop NameNode Service Not Running Properly?

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Problem scenario
The Hadoop NameNode service won’t start.  You run start-dfs.sh and it starts the SecondaryNameNode and the DataNode.  It won’t start the NameNode.

Solution
Assumption: This solution only works if you are running the start-dfs.sh as a sudo user or the root user itself.

Procedures
Verify you can ssh with root to the localhost.  Run this command twice without exiting from the first session: 

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What Is an ARM in Modern Information Technology Vernacular?

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Question
What Is an ARM in Modern Information Technology Vernacular?

Answer / Disambiguation
In I.T. jargon the term ARM can refer to a number of different things.  Here are some potential definitions of this acronym in random order:

#1  Azure Resource Manager is a component of Azure.  It can be interacted with in the console if you log into a Azure via a web browser. 

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How Do You Create a Linux Server in Azure with PowerShell When You Keep Getting an Error “Status Code: 400…Bad Request”?

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Problem scenario
You are trying to create a Linux server in Azure with the Azure Tools for PowerShell.  You receive this message:

“Destination path for SSH public keys is currently limited to its default value due to a known issue in Linux provisioning agent.”

You see  “StatusCode: 400 … ReasonPhrase: Bad Request.”

What do you do to create an Ubuntu 16.x server and not get this error?

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How Do You Troubleshoot the Error “WARN conf.Configuration: bad conf file: element not < property >”?

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Problem scenario
You are trying to start HDFS.  But you get this error: “WARN conf.Configuration: bad conf file: element not <property>”

What should you do?

Solution
Look at mapred-site.xml, hdfs-site.xml, and core-site.xml files.  Verify you have a <property> tag in each file.

cat /path/to/mapred-site.xml | grep -i property
cat /path/to/hdfs-site.xml | grep -i property
cat /path/to/core-site.xml | grep -i property

If there is no <property>

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How Do You Install an Older Version of Jenkins (e.g., 1.x) on Ubuntu Linux?

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Problem scenario
Your enterprise’s policies are to install a version of Jenkins that is lower than the latest.  How do you install Jenkins 1.651.1 on Ubuntu 16.04?

Solution
1.  Install Java.  See this posting if you do not know how.
2.  Run these three commands to install Jenkins 1.651.1 (but you can chance the version whichever one is available):

curl -L https://pkg.jenkins.io/debian-stable/binary/jenkins_1.651.1_all.deb /tmp/jenkins_1.651.1_all.deb
sudo apt-get -y install daemon
sudo dpkg -i /tmp/jenkins_1.651.1_all.deb

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How Do You Install Maven, openjdk, libssl-dev, build-essential, and pkgconf on a RedHat 7.X or CentOS 6.X Linux Server?

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Problem scenario
You are using a RedHat derivative distribution of Linux (e.g., CentOS/RHEL/Fedora).  To eliminate a Hadoop error, you need to install a variety of packages.  How do you install Maven, openjdk, libssl-Dev, build-Essential, and pkgconf?

Solution
To install Maven, see this article.

For the rest of the packages, run these commands:

sudo yum -y install java-1.8.0-openjdk-devel openssl-devel cmake protobuf

sudo yum -y groupinstall ‘Development Tools’

curl ftp://rpmfind.net/linux/fedora/linux/updates/25/x86_64/p/pkgconf-1.3.7-1.fc25.x86_64.rpm pkgconf-1.3.7-1.fc25.x86_64.rpm

curl ftp://rpmfind.net/linux/fedora/linux/updates/25/x86_64/l/libpkgconf-1.3.7-1.fc25.x86_64.rpm libpkgconf-1.3.7-1.fc25.x86_64.rpm

sudo rpm -ivh *.rpm …

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How Do You Troubleshoot a Chef Client That Has the Results of “knife client list” as “404 not found”?

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Problem scenario
You set up Chef server and Chef client on Linux servers.  On the Chef client server you run this command:

knife client list

You get this as the output:

ERROR: The object you are looking for could not be found
Response: <!DOCTYPE html>
<html xmlns=”http://www.w3.org/1999/xhtml”>
<head>
  <meta http-equiv=”Content-Type” content=”text/html; charset=utf-8″ />
  <meta http-equiv=”X-UA-Compatible” content=”IE=EmulateIE7″ />

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How Do You Create a Certificate Signing Request (CSR) File and Set up an HTTPS Server for Basic Testing?

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Problem scenarios
This is a two-in-one posting.  The same solution works for two different problem scenarios.

Problem scenario A
You want to create a certificate signing request permissions file (a csr.pem) to learn more about it.  You also want to try to use HTTPS as a test.  How do you do these things?

Problem scenario B
You want to implement a solution with TLS. 

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