A Technical I.T./DevOps Blog
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.,
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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,
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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
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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.
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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.
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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.
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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.
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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?
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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/
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Problem scenario
You are trying to install Darling. You get this error: “./include/linux/uio.h:16:31: fatal error: 1/hash.h: No such file or directory
#include RH_KABI_HIDE_INCLUDE()”
What should you do?
Solution
Run this:
sudo uname -r
Is the kernel version 5 or higher? If not, that is the root cause.
The source of this was https://github.com/darlinghq/darling/issues/975
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