How Do You Troubleshoot “ERROR: Hadoop common not found” when Running Hadoop?

Problem Scenario
You run an HDFS command, but you get this message: "ERROR: Hadoop common not found"

What should you do?

Solution
As the hduser or user that runs hdfs, log in. Run "echo $HADOOP_HOME"

That directory should have a libexec directory with a file called hadoop-config.sh.

Run this: ls -lh $HADOOP_HOME/libexec

One way to create it is this: 1) find a hadoop-config.sh file (e.g., with a "sudo find / -name hdfs-config.sh" command). 2) run this command sudo ln -s /path/to/hdfs-config.sh $HADOOP_HOME/libexec/hadoop-config.sh

Be mindful of the "hadoop-config.sh" and "hdfs-config.sh" difference; it is subtle.

(This is the for open source version and not a specific vendor's implementation of Hadoop.)

In I.T., what is a Schema?

Question
In computing, what is the definition of a schema?

Answer / schema disambiguation
Outside of the I.T. realm, Merriam-Webster's Dictionary (11th Edition, on page 1110) defines schema as "a diagrammatic presentation; broadly: a structured framework or plan: outline." This definition must have influenced the appropriation of the word to refer to concepts in I.T..

For Kubernetes
"Schemas are the set of JSON files for various Kubernetes versions, extracted from the OpenAPI definitions." (Taken from https://medium.com/trendyol-tech/how-can-we-accomplish-our-kubernetes-schemas-validation-against-our-clusters-e521af390322 .) Schemas can be downloaded from GitHub (e.g., in the form of a .tar.gz file) and uncompressed on to a server or pod.

For relational databases
In relational databases a schema defines relationships and the inner configurations of the database such as foreign key constraints between tables (per this posting https://stackoverflow.com/questions/29155012/referencing-the-foreign-key-of-another-schema).

A schema can be thought of a blueprint inside the database (per
https://techmonitor.ai/what-is/what-is-schema-4944519).

As there are many different types of relational databases, each one tends to have a different type of schema. For example, there are details about Oracle, PostgreSQL and SQL Server schemas that vary from product to product. Schemas can be specific to users, tables or other objects.

In some contexts, different types of schemas become important such as logical or physical schemas; to read about the differences of these types of schemas, see this https://stackoverflow.com/questions/22067378/what-is-the-difference-between-logical-schema-and-physical-schema/22069941#22069941

To learn about a user's schema in Oracle, see this: https://docs.oracle.com/cd/B19306_01/server.102/b14220/schema.htm

In SQL databases the DROP SCHEMA command (note that "DROP" is a DDL, not a DML, command) will remove the schema and the objects related to that schema.

To view the schema that governs a table in MySQL, use the "DESCRIBE" command like this (but replace "foo" with the database name and "bar" with the table name):

DESCRIBE foo.bar

(This was adapted from https://www.tutorialspoint.com/how-do-i-show-the-schema-of-a-table-in-a-mysql-database .)

For XML

An XML schema will define the elements of one or more XML files. Here is an example:


 <?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

<xs:element name="note">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="to" type="xs:string"/>
      <xs:element name="from" type="xs:string"/>
      <xs:element name="heading" type="xs:string"/>
      <xs:element name="body" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

</xs:schema>

It was taken from https://www.w3schools.com/xml/schema_intro.asp

Another definition (with a very similar example) can be found here: https://techterms.com/definition/schema

XSD stands for XML Schema Definition. A pom.xml file for Maven may refer to an .xsd file. To see an XML, click here.

For Terraform
See this internal posting.

For Pulumi
See this internal posting.

What Musical Instruments Did the Signers of the Declaration of Independence Create?

Question
Some of the signers of the Declaration of Independence invented new musical instruments. Who were they and what did they invent?

Answer
Francis Hopkinson invented the Bellarmonic that involved steel bells (https://loc.gov/item/ihas.200035713). Ben Franklin invented the armonica (https://pubmed.ncbi.nlm.nih.gov/11855437/). To listen, click on this: https://www.youtube.com/watch?v=eEKlRUvk9zc

Digital Upgrades to Keep Your Business from Falling behind

Digital Upgrades to Keep Your Business From Falling Behind

Businesspop.net shares a post today intent on helping small businesses get ahead in the digital age.

As a small business owner, you have a lot on your plate. You have to keep your profits in the black, make sure that your customers are happy, and ensure your employees have the tools they need to be effective. Fortunately, these things are made easier through digital innovation. Here are a few bits of technology that are easy to integrate.

Business Process Management

We’ll get the most confusing out of the way first: business process management (BPM). Business process management is simply the act of installing software and improving your business operations by streamlining. This way, you reduce time by automating aspects of certain tasks. Business process management can be thought of as a framework instead of a specific program, and, no matter what you choose, you’ll want to keep an eye on its effectiveness and make tweaks to improve efficiency and performance. A quick note here is to make sure that any technology you add to your business will be fully supported. You can do this by calling tech support to see if you get a live human or the digital runaround.

SMS Communications

Text messaging is one of the best ways to reach your customers and, in fact, customers tend to prefer text and email over any other type of communication. This doesn’t mean you have to text your customers individually, and there are many apps and programs you can use to send monthly marketing communications and even personalize promotions. A few of these include Twilio and Mobile Text Alerts. Wholesale SMS marketing company HORISEN explains that there are many benefits of switching to an SMS platform, including low-cost, global reach, and having a direct link to your customers.

Digital Marketing

In addition to SMS, there are many other digital marketing platforms that can help you improve your operations. This includes things like social media, influencer, video, and display marketing and advertising. 99 Designs offers more information on these and six other important digital marketing avenues that all small businesses should consider.

Data Visualization

Data visualization is taking complex information and squishing it down into an easy-to-read format. Charts, graphs, and infographics are great examples of visualized data. You can use this in your small business to easily relay information and insight to your customers, employees, and even shareholders. These snapshots help your audience to determine which data is worth diving deeper into and which they’d rather leave at face value. This can save time and money and help everyone make better decisions.

In our digitally-advanced world, technological tools are available for businesses of all sizes. Don’t let the competition speed ahead of you on the information superhighway. Spend the time now implementing even simple upgrades, and you may very quickly see a return on your investment in time, efficiency, and profitability.

Visit the Continual Integration blog often for more tech topics.

Image via Pexels

Disclosure

This article was brought to you by Businesspop.net.

How Do You Troubleshoot the Error Message “usermod: group ‘wheel’ does not exist”

Problem scenario
You run "sudo usermod -aG wheel jdoe" but you get "usermod: group 'wheel' does not exist." What should you do?

Possible solution #1
Run this:

sudo usermod -aG admin jdoe

Some Linux distributions such as Ubuntu* use "admin" instead of "wheel"

You may want to read this for further information.

How Do You Troubleshoot /etc/sudoers Changes Not Working?

Problem scenario
You modified the /etc/sudoers file. The changes do not seem to have taken effect. What should you do?

Solution
99% of the time you do not need to log out or log back in. You should not need to open another terminal. For the stanza that you added, did you append it to the bottom? The problem may be that the stanza you added was in the middle of the file. If you are new to editing the /etc/sudoers file, try putting the stanza at the bottom. The changes should take effect instantaneously.

How Do You Troubleshoot “Segmentation fault” Errors in Hadoop/HDFS?

Problem scenario
You get a "Segmentation fault" or "Segmentation fault (core dumped)" error when you run any "hdfs" command. (This is open source Hadoop and not a proprietary, or vendor's, version.) What should you do?

Solution

Root cause
There is probably an infinite loop/recursion problem. (Segmentation faults involve writing to the stack. Eventually the memory gets filled up.) There is some configuration problem with your Hadoop / hdfs installation. If the installation used to work, look at backup configurations in Git. If it never worked, this problem will not be easy to correct/fix.

Possible solution
Reinstall Hadoop. You may want to see this posting for assistance.

What Is the Difference between aquota.user and quota.user?

Problem scenario
You found some empty files called aquota.group or quota.group. What is the difference?

Solution
The aquota.user file is for version 2 quota systems (per the man page for edquota). quota.user is for version 1. See also What Is the Difference between Version 1 Quotas and Versions 2 Quotas?

For Databases Is a B-Tree the Same as an Index?

Question
In the context of databases, Is a B-tree the same as an index?

Answer
For many intents and purposes they are the same.

"B-Tree is a self-balancing search tree." Taken from
https://www.geeksforgeeks.org/introduction-of-b-tree-2/

"B-tree is a data structure that store data in its node in sorted order."
https://dzone.com/articles/database-btree-indexing-in-sqlite

This source says that the "B" stands for "balanced" (not "binary"): https://use-the-index-luke.com/sql/anatomy/the-tree

To learn more see this: https://www.geeksforgeeks.org/difference-between-binary-tree-and-b-tree/