A Technical I.T./DevOps Blog
Problem scenario
You want to retrieve lines from a log file with the word "failed". How do you do this with Python?
Solution
Assuming the log file is named "auth.log", this will work:
log_reader = open('auth.log', 'r')
for line in log_reader:
lower_line = line.lower()
if lower_line.find("failed") != -1:
print(line)Problem scenario
You are trying to remove curl with dnf or yum commands. You cannot do it because dnf or yum requires curl. What should you do to reinstall curl?
Solution
Prerequisites
You need make installed. If you need assistance with this, see this posting.
Procedures
Manually back up then delete curl. Run "which curl". Move it to a user's home directory.
Go here: https://curl.haxx.se/download/?C=M;O=D
Get a link to the .tar.gz media. Download it.
Use commands like this to expand the files and install curl:
copy the file downloaded into /opt/
tar -zxvf NameOfFileAbove.tar.gzcd into the directory created
Run commands such as these:
./configure
make
sudo make installProblem scenario
You have a web page with a table. It uses HTML and Javascript. You want only a sub-portion of the rows to be displayed and allow the user from the front-end to click a drop down menu to see more results. What should you do?
Possible Solution #1
Have two blocks in the .html file. Have the top one define a function that accepts a parameter and filters the table results if/when called. The parameter will accept a variable (e.g., a Boolean). The function will have conditional logic based on this Boolean value.
Have the lower block invoke the function. This function can be invoked with a drop down menu (associated with an event from the front-end of the web page). This function can be invoked in the Javascript code embedded in the .html file or in a separate .js file (referenced in the .html file).
Possible Solution #2
Use DataTables (the JQuery plugin) in Javascript code. HTML can have embeddeed Javascript (between tags) or refer to a separate .js file.
"DataTables is a powerful Javascript library for adding interaction features to HTML tables." Taken from https://www.c-sharpcorner.com/article/create-datatable-in-jquery/
The Javascript code can have stanzas such as these:
…
bpaginate: true,
bLengthChange: true,
…You can read more about them here. Here is an example of how to do it: https://www.programmersought.com/article/44601760749/
Problem scenario
You want to install a feature rich screen capture video software program that can record via a camera too. What do you do?
Solution
Prerequisite
Install snap: sudo dnf install snapd
sudo snap install obs-studio
# If you are using Fedora 32, run this command:
sudo dnf install http://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-32.noarch.rpm
# If you are using a different version of Fedora, see this external page: http://download1.rpmfusion.org/free/fedora/
sudo dnf install obs-studio-libs
sudo dnf install qt5-qtsvg
# Run these commands:
sudo find / -name librtmp.so.1
sudo ln -s <pathFoundAbove> /lib64/Problem scenario
You try to run obs (Open Broadcaster Studio Software) on Fedora, but you get a message like this:
/var/lib/snapd/snap/obs-studio/1195/usr/bin/obs: error while loading shared libraries: libQt5Svg.so.5: cannot open shared object file: No such file or directoryWhat should you do?
Solution
Run this command:
sudo dnf install qt5-qtsvgProblem scenario
The built-in camera of your laptop or desktop is not working. What should you do?
Possible Solutions
These links may also help:
https://www.technewstoday.com/laptop-camera-not-working/
https://www.youtube.com/watch?v=KOJHbJxiJZ8
https://www.youtube.com/watch?v=NSXPZYlV1sY
https://www.youtube.com/watch?v=w6geNk3QnBQ
https://www.youtube.com/watch?v=uggw6Bnlsjs
For a Windows computer, you may want to try these:
https://support.wepow.com/hc/en-us/articles/360021426334-My-Lenovo-camera-isn-t-working
https://windowsreport.com/fix-laptop-camera-wont-work/
For a Mac, you may want to try these:
https://support.apple.com/en-us/HT211130
https://setapp.com/how-to/fix-camera-on-mac-not-working
https://nektony.com/how-to/fix-mac-camera-not-working
https://www.igeeksblog.com/macbook-camera-not-working/
For a Linux system with a USB-connected camera, see this.
For a USB-connected camera, see this.
Problem scenario
You have installed Open Broadcaster Software. You know want to run the GUI application. What do you do?
Solution
From a terminal window, run this command:
sudo find / -name obs -type fRun the file that is found as a command.
Problem scenario
You are designing a Flask application with Python running some long-running processes. You want to handle the requests asynchronously. The individual requests will have a duration of more than one hour. What is the recommended way of handling this?
Solution
Use a task queue like Celery or RQ (Redis Queue).
Sources:
https://stackoverflow.com/questions/42790362/how-to-handle-long-sql-query-in-flask
Problem scenario
You want to extend Kubernetes' functionality. You want to use CustomResourceDefinitions. You can view API resources by running "kubectl api-resources". You want to add to the list. How do you use a CRD?
Solution
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
name: contintexamples.continualintegration.com
spec:
group: continualintegration.com
names:
kind: ContintExample
plural: contintexamples
listKind: ContintExampleList
singular: contintexample
scope: Namespaced
versions:
- name: v1
# Each version can be enabled/disabled by Served flag.
served: true
# One and only one version must be marked as the storage version.
storage: true
schema:
openAPIV3Schema:
type: object
properties:
spec:
type: object
properties:
owner:
type: string
description: The name of the owner of this Contint Example franchise
address:
type: string
description: The physical address of the Contint Example
currency:
type: string
description: The currency which this Contint Example accepts payments in
replicas:
type: integer
description: The number of instances of the Contint Example app to deploy
additionalPrinterColumns:
- name: Owner
jsonPath: .spec.owner
type: string
- name: Currency
jsonPath: .spec.currency
type: string
- name: Replicas
jsonPath: .spec.replicas
type: integer
- name: Age
jsonPath: .metadata.creationTimestamp
type: date(# The above file was adapted from https://www.tutorialworks.com/kubernetes-custom-resources/ )
2. Run this: kubectl apply -f contint.yaml
3. You have now created a CustomResourceDefinition. The below steps 3a, 3b, 3c, 3d, and 3e are optional.
3.a. Run kubectl api-resources to view what API resources are currently at your disposal. Run kubectl get crd to view what you already may exist.
3.b. Run kubectl get crd to view what you created among everything else that was already there.
3.c. Run kubectl describe crd contintexamples.continualintegration.com to view the details.
3.d. Run kubectl api-resources to view what API resources are currently at your disposal.
3.e. Test it by running this: kubectl api-resources --api-group=continualintegration.com
Question
When you have high availability of servers, you have seen diagrams with a "sink" server. What does the word "sink" signify?
Answer
A sink, homophonic with "sync", is a secondary server in a cluster or replication configuration. That is, there is a primary server that is actively processing transactions of databases or registering changes to files. This primary server may replicate changes over to a secondary or sink server. The sink server receives the changes secondarily from the primary server.