A Technical I.T./DevOps Blog
Problem scenario
You want to change the main configuration file for Apache web server (e.g., httpd.conf). But you do not want to drop current web surfers viewing the website. How do you change a security module or listening port for an Apache web server and have the changes take effect without interrupting the service by doing a regular restart?
Solution
Use the “graceful” directive.
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Problem scenario
You are trying to install open source Accumulo on Linux. You have two GB of swap space. You have installed Java, Hadoop, and Zookeeper. You have run the bootstrap_config.sh script for Accumulo 1.9.2.
You run this (and expected it to work): /bin/accumulo-1.9.2/bin/accumulo init
But you get this error:
OpenJDK 64-Bit Server VM warning: If the number of processors is expected to increase from one, …
Continue reading “How Do You Troubleshoot the Installation of Apache Accumulo on Linux?”
Problem scenario
You want to set up Zookeeper with three nodes in AWS. What do you do?
Solution
1. Install Zookeeper on each of the servers. If you need assistance with this, see this posting.
2. Modify the zoo.cfg file on each of the servers. Add stanzas like these but substitute foobarX.amazonaws.com with the Public DNS name of each server:
server.1=foobar1.amazonaws.com:2888:3888
server.2=foobar2.amazonaws.com:2888:3888
server.3=foobar3.amazonaws.com:2888:3888
initLimit=5
syncLimit=5
3.
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Continue reading “How Do You Set Up a Multi-Node Cluster of Zookeeper?”
Problem scenario
You want to create a database in MongoDB using the CLI. How do you do this from a Linux server and then add a document to the database you just created?
Solution
Prerequisite
Install MongoDB on a Linux server; if you need assistance, see this posting.
Procedures
1.a. Enter the MongoDB shell: /usr/bin/mongo
1.b.
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Continue reading “How Do You Create a Database in MongoDB Not Using using Compass (the GUI)?”
Problem scenario
You have heard of A records and PTR records. But you do not know the difference. What is the difference?
Solution
The short answer is that they are opposites of each other in the context of DNS.
An A record maps a domain name to an IP address (pg 858 of A Practical Guide to Fedora and Red Hat Enterprise Linux).
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Continue reading “What Is The Difference between an A Record and a PTR Record in DNS?”
Problem scenario
You use a variable in an Ansible playbook. The value of the variable is surrounded by quotes and brackets. You may refer to it as punctuation [“”]. You want to assign the variable without the new symbols such as ‘[“”]’. How do you get just the value and no punctuation?
Solution
Do not use quotes or square brackets “[]” around the variable.
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Problem scenario
You have configured Nginx to be an HTTP load balancer (a web server configured to behave as a landing portal that enables traffic to pass through). As a reverse proxy with built-in keywords you have use the “least_conn” directive, but it does not seem to be working. You want inbound network connection requests from your users via web browsers to be relayed to the web servers with the fewest (or least) amount of active connections.
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Continue reading “How Do You Use the least_conn Directive in an Nginx Configuration File?”
One or both of the following scenarios applies.
Problem scenario #1
Try to install kubectl, but you get an error message about it being installed.
Problem scenario #2
You run “man kubectl” but you see no man page. You still think kubectl is installed.
What should you do?
Solution
Run this command: kubectl version
The results should give you some clues as to what is wrong.
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Continue reading “How Do You Know if kubectl Is Installed on Your Linux Server?”
Question
What is SELinux?
Answer
Security-Enhanced Linux (or SELinux) is a kernel module that can be installed and turned on in a Linux server. It categorizes files, hardware resources and processes; to learn more see this posting. It has the ability to restrict access to these categories. If a server is designated as an application server, a database server, or a web server,
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Problem Scenario
You run a “kinit” command. But you receive this:
‘kinit: Cannot find KDC for realm “CONTINUALINTEGRATION.COM” while getting initial credentials’
What should you do?
Solution
Look at the /etc/krb5.conf file. Look at the REALM section. Does it look like this?
[realms]
EXAMPLE.COM =
You need to change “EXAMPLE.COM” to your domain name.
Look also at the libdefaults section.
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