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167 entries match these filters

0320 Fix: address already in use (EADDRINUSE) Something is already listening on the port your program wants. Find the process with lsof or ss, stop it or pick another… Beginner · Fixes an error · Linux, macOS Article Networking & firewalls · Node.js · Processes & ports 15 Oct 2026
0321 Fix: E: Unable to locate package / could not get lock /var/lib/dpkg/lock Two apt errors with simple causes: Unable to locate package means the package lists are stale or the name is wrong; could… Beginner · Fixes an error · Linux Article Packages & updates 15 Oct 2026
0322 Fix: user is not in the sudoers file sudo refuses because your account is not allowed to use it. Add the user to the sudo group (Debian, Ubuntu) or wheel… Beginner · Fixes an error · Linux, macOS Article Server hardening · Users, sudo & hardening 15 Oct 2026
0323 Fix: Failed to start service, how to read systemctl status and journalctl Job for x.service failed tells you only that the service did not start. The real reason is in systemctl status and journalctl… Beginner · Fixes an error · Linux Article Logs · Services & systemd 15 Oct 2026
0327 Docker images, containers and volumes explained An image is a read-only template, a container is a running copy of it with a thin writable layer, and a volume… Beginner · Explains an idea · Linux, macOS, Windows Article Docker basics 15 Oct 2026
0328 Install Docker Engine on Ubuntu and Debian Set up Docker's official apt repository, install Docker Engine with the Compose and Buildx plugins, run hello-world and let your user run… Beginner · Step by step · Linux Article Docker basics · Packages & updates 15 Oct 2026
0329 Docker CLI cheat sheet The Docker commands you reach for every day, grouped by what they act on: containers, images, volumes, networks, logs and cleanup, with… Beginner · Cheat sheet · Linux, macOS, Windows Article Docker basics 15 Oct 2026
0295 What is a transaction? A transaction groups several database changes so they all happen together or not at all, keeping the data consistent. Beginner · Explains an idea · Any system Article Queries 15 Oct 2026
0311 What is Kubernetes? Kubernetes is a system that runs containers across many servers, restarting, scaling and connecting them automatically. Beginner · Explains an idea · Any system Article Concepts 15 Oct 2026
0296 What is a primary key? A primary key is the column that uniquely identifies each row in a table, like an ID number nobody else can have. Beginner · Explains an idea · Any system Article Queries 15 Oct 2026
0312 What is a pod? A pod is the smallest unit Kubernetes runs: one or more containers that share a network address and storage. Beginner · Explains an idea · Any system Article Workloads & services 15 Oct 2026
0297 What is a foreign key? A foreign key is a column that points to the primary key of another table, linking related rows together. Beginner · Explains an idea · Any system Article Joins 15 Oct 2026
0313 What is CI/CD? CI/CD is the habit of automatically testing every code change and, once it passes, deploying it without manual steps. Beginner · Explains an idea · Any system Article Pipelines, runners & hooks 15 Oct 2026
0298 What is JSON? JSON is a simple text format for structured data, made of names, values, lists and nested objects, used everywhere on the web. Beginner · Explains an idea · Any system Article CSV & JSON 15 Oct 2026
0314 What is a pull request? A pull request asks teammates to review and merge the changes on your branch into the main branch. Beginner · Explains an idea · Any system Article Pull requests 15 Oct 2026
0299 What is YAML? YAML is a human friendly text format for configuration files where indentation shows structure instead of brackets. Beginner · Explains an idea · Any system Article CSV & JSON 15 Oct 2026
0315 What is open source? Open source software is software whose code anyone can read, change and share under a licence that allows it. Beginner · Explains an idea · Any system Article Pull requests 15 Oct 2026
0300 What is a REST API? A REST API is a web API where you use normal HTTP requests on URLs to read, create, update and delete things. Beginner · Explains an idea · Any system Article Making requests 15 Oct 2026
0316 Fix: command not found bash: something: command not found means the shell could not find a program with that name in any PATH directory. The usual… Beginner · Fixes an error · Linux, macOS Article Basics · Packages & updates 15 Oct 2026
0301 What is HTTP? HTTP is the request and response language that browsers, apps and servers use to exchange web pages and data. Beginner · Explains an idea · Any system Article Making requests 15 Oct 2026
0317 Fix: Permission denied when running a script (chmod +x) bash: ./script.sh: Permission denied means the file exists but you may not execute it. Usually the execute bit is missing; sometimes the… Beginner · Fixes an error · Linux, macOS Article Basics · Users, sudo & hardening 15 Oct 2026
0302 What is a status code? A status code is the three digit number a web server returns to say whether a request worked, like 200 OK or… Beginner · Explains an idea · Any system Article Status codes 15 Oct 2026
0318 Fix: fatal: not a git repository Git looked in the current directory and every parent for a .git folder and found none. You are in the wrong directory,… Beginner · Fixes an error · Any system Article Common errors · Setup 15 Oct 2026
0303 What is CORS? CORS is a browser rule that decides whether a web page from one site is allowed to call an API on another… Beginner · Explains an idea · Any system Article Making requests 15 Oct 2026
0319 Fix: npm ERR! EACCES permission denied npm cannot write to a directory it needs: the global install location, its cache in ~/.npm, or a node_modules owned by root.… Beginner · Fixes an error · Linux, macOS Article Common errors · Node.js 15 Oct 2026
0304 What is a cookie? A cookie is a small piece of text a website stores in your browser so it can recognise you on the next… Beginner · Explains an idea · Any system Article Authentication 15 Oct 2026
0289 What is a process? A process is a running program; the operating system gives each one its own memory and an ID number. Beginner · Explains an idea · Any system Article Processes & ports 15 Oct 2026
0305 What is a token? A token is a string that proves who you are or what you may do, sent with requests instead of a password. Beginner · Explains an idea · Any system Article Authentication 15 Oct 2026
0290 What is a cron job? A cron job is a command scheduled to run automatically at set times, such as every night at two o'clock. Beginner · Explains an idea · Any system Article cron & timers 15 Oct 2026
0306 What is hashing? Hashing turns any data into a fixed length fingerprint that cannot be reversed, used to check files and store passwords. Beginner · Explains an idea · Any system Article Secrets & access 15 Oct 2026
0291 What is a log? A log is a running record of what a program did and when, written to a file so you can look back… Beginner · Explains an idea · Any system Article Logs 15 Oct 2026
0307 What is encryption? Encryption scrambles data with a key so only someone with the right key can read it again. Beginner · Explains an idea · Any system Article TLS & certificates 15 Oct 2026
0292 What is a database? A database is an organised store of data that programs can search, update and share safely, even with many users at once. Beginner · Explains an idea · Any system Article Choosing a database 15 Oct 2026
0308 What is a backup snapshot? A snapshot is a frozen picture of a disk or system at one moment that you can roll back to if something… Beginner · Explains an idea · Any system Article Strategy & restore drills 15 Oct 2026
0293 What is SQL? SQL is the language you use to ask a relational database questions and to add, change or delete its data. Beginner · Explains an idea · Any system Article Queries 15 Oct 2026
0309 What is RAID? RAID combines several disks into one so data survives a disk failure or is read and written faster. Beginner · Explains an idea · Any system Article Disks, LVM & filesystems 15 Oct 2026
0294 What is an index (database)? A database index is a lookup structure that lets the database find rows fast instead of reading the whole table. Beginner · Explains an idea · Any system Article Indexes & performance 15 Oct 2026
0310 What is a cluster? A cluster is a group of computers working together as one system so that if one fails the others keep the service… Beginner · Explains an idea · Any system Article Clusters & high availability 15 Oct 2026
0279 What is a reverse proxy? A reverse proxy is a server that sits in front of your apps, receives all requests and forwards them to the right… Beginner · Explains an idea · Any system Article Web servers & reverse proxies 15 Oct 2026
0280 What is a firewall? A firewall is a filter that decides which network connections are allowed in or out of a computer or network. Beginner · Explains an idea · Any system Article Firewalls 15 Oct 2026