Linux Fundamentals
The Filesystem
Last Updated: September 16, 2026Linux doesn’t have drives. It has one tree, and everything hangs off a single root. There’s no C: drive here Windows organizes itself around drive letters — C:\, D:\. Linux does something simpler: one single tree, starting at /, called the root directory. Every file and folder on the system lives somewhere underneath it. /...
Quick Knowledge Check
Last Updated: September 16, 2026Ten questions. Click each one to reveal the answer. What does / represent?show answer The root directory of the Linux filesystem — the single starting point everything else hangs off. What does ~ represent?show answer The current user’s home directory. How do you find your current directory?show answer pwd How do you move to the...
The Mental Model
Last Updated: September 16, 2026Five layers. Five things to remember. If everything else fades, keep these. LINUX │ ┌───────────┼───────────┐ ↓ ↓ ↓ Filesystem Processes Networking │ │ │ pwd/ls/cd ps/top/kill ping/curl/ssh │ ↓ Permissions │ chmod/chown │ ↓ Shell │ | > >> sudo The five things 1. Linux is filesystem-oriented Everything starts from /, and paths tell you...
Command Cheat Sheet
Last Updated: September 16, 2026div class=”bct-lesson”> Every command from this series, in one scannable table. Area Command Purpose Location pwd Show current directory Listing ls List files Navigation cd Change directory Directory mkdir Create directory Delete rm Remove files/directories Copy cp Copy files/directories Move mv Move / rename File touch Create empty file / update timestamp View cat Display...
The Troubleshooting Flow
Last Updated: September 16, 2026“What command should I run?” is the wrong first question. Systematic beats clever, every time. An application on a Linux server stops working. A beginner asks “what command fixes this?” A DevOps engineer instead works through a sequence — and almost every step uses a command from the earlier chapters. 1 · Where am I?pwd...
Putting It Together
Last Updated: September 16, 2026A small end-to-end exercise that uses almost everything from the last five chapters in one sitting. You’ve just SSH’d into a server. Here’s a realistic sequence, start to finish: ssh alice@192.168.1.10 pwd ls -la mkdir devops cd devops touch application.log echo "Application started" > application.log echo "Database connected" >> application.log cat application.log grep Database application.log...
Other Essentials
Last Updated: September 16, 2026sudo, pipes, redirects, and man pages — the connective tissue that makes every other command more powerful. sudo — borrowing admin rights sudo apt update # run this command with administrative privileges The pipe: | This might be the single most powerful idea in the entire shell: the output of one command becomes the input...
Package Management
Last Updated: September 16, 2026Different distros, different tools — but the same two ideas: refresh the list, then install or upgrade. apt (Ubuntu / Debian) sudo apt update # refresh the list of what's available sudo apt install nginx sudo apt upgrade # actually install the upgrades The distinction people mix up: apt update does not upgrade anything —...
Networking
Last Updated: September 16, 2026Servers rarely work alone. These five commands are how Linux machines talk to each other — and how you prove they can. ping — the simplest connectivity check ping google.com # 64 bytes from ... → responses are coming back A failed ping doesn’t always mean the server is down. Firewalls frequently block ICMP traffic...
Permissions
Last Updated: September 16, 2026Three letters, three numbers — and once the math clicks, chmod stops feeling like a guessing game. Reading the output of ls -l -rwxr-xr-- 1 alice developers 120 Sep 15 app.sh Break the permission string into four pieces: – rwx r-x r– │ │ │ │ │ │ │ └── Others │ │ └─────── Group...
Processes
Last Updated: September 16, 2026Every running program is a process with an ID — and three commands cover almost everything you need to know about it. What a process is The moment you run python app.py, Linux creates a process for it and hands it a unique number — the PID (Process ID). That number is how you’ll refer...
Viewing Files
Last Updated: September 16, 2026Once you can find files, the next skill is reading them — especially logs, without opening an editor. cat and less cat dumps a whole file to the screen — fine for something short. For anything long, less lets you scroll one screen at a time instead of flooding your terminal. cat notes.txt less server.log...
Navigation & Files
Last Updated: September 16, 2026pwd, ls, and cd are the three commands you’ll type more than any others, ever. The three you’ll never stop typing Think of these as one loop you run constantly: pwdWhere am I? ↓ lsWhat’s here? ↓ cdTake me somewhere else. pwd # print working directory ls # list what's in it ls -la #...
Labs to Practice
Last Updated: September 16, 2026Seven scenarios, in order. Each one builds on the last — do them on WSL, an Azure VM, or play-with-docker.com. Scenario 1 — Find your way around Open a terminal Print your current directory List all files, including hidden ones Navigate to /etc and list its contents Come back home Scenario 2 — Create and...