4 Systems & infrastructure

Every entry filed under Systems & infrastructure and its subtopics.

238 entries

0337 docker/compose The source of Docker Compose, the tool that defines and runs multi-container applications from a compose.yaml file. Useful for release notes, the… Linux, macOS, Windows Repo Docker Compose 15 Oct 2026
0325 Fix: SSL certificate problem: unable to get local issuer certificate curl, git, pip or npm cannot chain the server's certificate to a root they trust. Usual causes: a corporate proxy that re-signs… Intermediate · Fixes an error · Linux, macOS, Windows Article Common errors · Making requests · TLS & certificates 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
0341 DNS, IP addresses and ports explained for beginners An IP address says which machine, a port says which program on it, and DNS turns names into addresses. The three ideas… Beginner · Explains an idea · Linux, macOS Article DNS, IP addresses & ports 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
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
0343 Fix: Connection refused and Connection timed out, what each one means Refused means the host answered and nothing is listening there. Timed out means no answer at all, usually a firewall or wrong… Beginner · Fixes an error · Linux, macOS Article DNS, IP addresses & ports · Firewalls 15 Oct 2026
0330 Write a Dockerfile: FROM, COPY, RUN, CMD and multi-stage builds How a Dockerfile turns into an image layer by layer, what the main instructions do, how to order them for fast rebuilds,… Intermediate · Step by step · Linux, macOS, Windows Article Docker basics · Images & registries 15 Oct 2026
0333 Fix: permission denied while trying to connect to the Docker daemon socket Every docker command fails with permission denied on /var/run/docker.sock. The daemon is fine; your user is not allowed to use its socket.… Beginner · Fixes an error · Linux Article Docker basics · Docker fixes 15 Oct 2026
0335 Docker cleanup script with dry run and confirmation A bash wrapper around docker system prune that shows disk usage and lists what would be removed, supports a dry-run flag, and… Beginner · Step by step · Linux, macOS Script Docker basics · Shell scripting 15 Oct 2026
0332 Tag, push and pull images with Docker Hub and other registries How image names map to registries, how to log in, tag and push an image to Docker Hub, GitHub Container Registry or… Intermediate · Step by step · Linux, macOS, Windows Article Images & registries 15 Oct 2026
0336 Back up and restore a Docker named volume to a tar archive A bash script that copies the contents of a named Docker volume into a .tar.gz on the host, and restores an archive… Intermediate · Step by step · Linux, macOS Script Backup tools · Docker basics 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
0338 Watchtower (maintained fork): automatic container image updates Watchtower watches your running containers, pulls newer versions of their images and restarts them with the same settings. This fork continues the… Linux Repo Docker basics · Images & registries 15 Oct 2026
0334 Fix: port is already allocated docker run or docker compose up fails with Bind for 0.0.0.0:8080 failed: port is already allocated. Find what holds the port, another… Beginner · Fixes an error · Linux, macOS, Windows Article Docker fixes · Processes & ports 15 Oct 2026
0339 Uptime Kuma: self-hosted uptime monitoring Uptime Kuma is a self-hosted monitoring tool with a web UI that checks websites, TCP ports, DNS, Docker containers and more, draws… Linux, macOS, Windows Repo Alerting & dashboards · Docker basics 15 Oct 2026
0340 Build and run a small Python web app in a container Write a tiny Flask app, give it a Dockerfile, build the image, run it with a published port, make a change and… Beginner · Guided project · Linux, macOS, Windows Article Basics · Docker basics · Images & registries 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
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
0331 docker compose for an app with a PostgreSQL database A compose.yaml that runs your application next to a PostgreSQL container, with a named volume for the data, a health check so… Intermediate · Step by step · Linux, macOS, Windows Article Docker Compose · Install & connect 15 Oct 2026
0326 Fix: too many open files A process hit its file descriptor limit, usually 1024. Raise it for the shell, the systemd unit or the user, fix a… Intermediate · Fixes an error · Linux, macOS Article Performance & tuning · Processes & ports · Services & systemd 15 Oct 2026
0342 Which process is using a port, and how to free it Find the program behind a busy port with ss, lsof or fuser, decide whether to stop it properly or kill it, and… Beginner · Step by step · Linux, macOS Article DNS, IP addresses & ports · Networking & firewalls 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
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
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
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
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
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
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
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
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
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
0273 What is a hypervisor? A hypervisor is the software layer that creates and runs virtual machines and shares the real hardware between them. Beginner · Explains an idea · Any system Article Basics 15 Oct 2026
0266 What is a port? A port is a numbered door on a computer that lets one machine run many network services at the same time. Beginner · Explains an idea · Any system Article DNS, IP addresses & ports 15 Oct 2026
0268 What is a container? A container is a lightweight box that packs a program with everything it needs so it runs the same on any computer. Beginner · Explains an idea · Any system Article Docker basics 15 Oct 2026
0274 What is DNS? DNS is the internet's phone book: it turns names like example.com into the IP addresses computers actually use. Beginner · Explains an idea · Any system Article DNS, IP addresses & ports 15 Oct 2026
0281 What is a package manager? A package manager is a tool that installs, updates and removes software for you and keeps track of what depends on what. Beginner · Explains an idea · Any system Article Packages & updates 15 Oct 2026
0275 What is an IP address? An IP address is the unique number that identifies a device on a network so data knows where to go. Beginner · Explains an idea · Any system Article DNS, IP addresses & ports 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