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

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

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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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How Do You Troubleshoot “fatal error: 1/hash.h: No such file or directory”?

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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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With Nginx Can a .pem file replace a .crt and/or a .key File?

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Problem scenario
You know .crt and .key files can pair as ssl_certificates and SSL certificate keys respectively. In Nginx, can .pem files replace .crt files? Can .pem files potentially replace .key files? Can a .pem file be a substitute?

Solution
Yes to some extent, for the nginx.conf file, a .pem file can replace a .crt file and potentially a .key file too.

To read more,

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How Do You Remove the Battery Cover of a Nokia Cell Phone?

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Problem scenario
You want to remove the battery from your Nokia flip phone. There is a hinge, and the phone closes as normal like a clamshell. But you need to restart the phone (e.g., and it will not shut off). How do you remove the battery from a Nokia phone?

Solution
While the phone back cover may seem hard to come off, it appears to have a door for the battery cover:

The rounded corners of the line appears to be a seam between two separate components of the back cover.

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How Do You Troubleshoot the Error “unable to prepare context…no such file or directory”?

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Problem scenario
You run “docker-compose build” and you get this:

1 error occurred:
* unable to prepare context: unable to evaluate symlinks in Dockerfile path: lstat /home/jane/dockercompose/webapp/Dockerfile: no such file or directory

What should you do?

Solution
Look at your docker-compose.yml file. Look at the “build” stanza. What directory is it referring to? Is a Dockerfile file in that directory?

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How Do You Get a Bluetooth Speaker to Work with Your Windows Laptop?

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Problem scenario
You turn on your laptop and Bluetooth wireless speaker. Your external speaker is not working. What should you do?

Possible Solution #1
Is the Bluetooth device on?

Possible Solution #2
Go to Control Panel -Hardware and Sound -Manage audio devices. Do you see a device that could be the wireless one? Click on it and view the properties.

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How Do You Create a docker.service File on a Linux Server?

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One of the following apply:

Problem scenario #1
You run this: “sudo systemctl start docker”
But you get this: “Failed to start docker.service: Unit docker.service not found.”

Problem scenario #2
You run this: “sudo systemctl start docker”
But you get this:
“docker.service: Service has no ExecStart=, ExecStop=, or SuccessAction=. Refusing.”
or this:
“Failed to start docker.service: Unit docker.service not found.”

Problem scenario #3
You run this: sudo systemctl enable docker
But you get this: “Failed to enable unit: Unit file docker.service does not exist.”

Solution
Use this posting.

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How Can You Test Your /etc/fstab File without Rebooting the Linux Server?

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Problem scenario
You want modified the /etc/fstab file. You want to reboot, but you are concerned your server won’t work if you accidentally had a typo in the /etc/fstab file. What should you do?

Solution

  1. Backup the /etc/fstab file somewhere (e.g., /etc/bak.fstab.bak).
  2. Run a command like this:

sudo mount -o remount,rw /dev/path/to /path/to/use

The /path/to/use is the path that you will see on your Linux system.

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