Linux Essentials & Open Source

1) What is Linux (in plain words)?

• Linux is an operating system like Windows/macOS. More precisely, Linux is the kernel—the core program that talks to hardware.

• A Linux distribution (distro) = Linux kernel + basic tools + desktop/server apps + a package manager (e.g., Ubuntu, Fedora, Debian, Arch, Kali).

Where you already meet Linux

Android phones, smart TVs/routers, cloud servers (AWS/GCP/Azure), supercomputers, Raspberry Pi, and many websites you visit daily.

2) Why Linux?

• Free & open source: no license fees; you can inspect/modify the code.

• Stable & secure: strong permissions model; fewer forced restarts.

• Fast & lightweight: runs well even on older hardware.

• Customizable: choose desktop environments, shells, and tools that suit you.

• Great for developers: built-in programming tools, servers, Docker, Git, Python, C/C++.

3) The big picture (how Linux is organized)

• Kernel: manages CPU, memory, disks, devices.

• Shell: the command interpreter (e.g., bash, zsh) you type into.

• Utilities: small programs that do one thing well (ls, cp, grep, …).

• Filesystem: single tree starting at / (root). Everything is a file.

• Package manager: install/update software (APT on Ubuntu/Debian, DNF on Fedora, pacman on Arch).

4) Try Linux quickly

Option A: WSL on Windows (fastest)

1.   Open PowerShell as Administrator.

2.   Run:

3. wsl --install -d Ubuntu

4.   Reboot if asked, then set a Unix username/password.

5.   Open Ubuntu app → you’re in a Linux terminal inside Windows.

Option B: VirtualBox (Windows/macOS/Linux)

1.   Install VirtualBox.

2.   Download a distro ISO (Ubuntu LTS is beginner-friendly).

3.   Create a VM → attach ISO → start → follow installer.

4.   Use Linux in a window safely (no changes to your main OS).

Tip: If your machine is older/low-RAM, choose Xubuntu or Lubuntu.

5) Filesystem basics (must-know)

• Case-sensitive: File.txt ≠ file.txt.

• Absolute path: starts with / (e.g., /home/rohit/docs).

• Relative path: from current folder (e.g., docs/report.txt).

• Home: ~ (e.g., /home/yourname).

• Hidden files: start with . (e.g., .bashrc).

• Common directories:

• /home user folders

• /etc config files

• /bin, /usr/bin programs

• /var variable data/logs

• /tmp temporary files

• /dev, /proc system/virtual files

6) Terminal 101

Command format:

command [options] [arguments]

Examples: ls -la, cp -r pics backup/

7) Everyday commands (with mini examples)

Safety: avoid rm -rf / or running sudo blindly. Use rm -ri to confirm.

8) Pipelines & redirection (superpower)

• Redirect output to file: > overwrite, >> append

·         ls -l > list.txt

• Pipe output of one command into another:

·         dmesg | grep usb

·         cat big.txt | wc -l

9) Permissions (r, w, x)

• Each file has permissions for user (u), group (g), others (o).

• ls -l shows like: -rwxr-xr-- user group file

• r=4, w=2, x=1 → add them:

• 7 = rwx, 6 = rw-, 5 = r-x, 4 = r--

• Change permissions:

·         chmod 754 script.sh    # u=rwx,g=rx,o=r

·         chmod u+x script.sh    # add execute for user

• Change owner/group (needs sudo):

·         sudo chown alice:devs report.txt

10) Processes & system monitoring

• See running processes: ps aux

• Interactive monitor: top (or htop if installed)

• Kill by PID: kill 1234 (polite), kill -9 1234 (force)

• Memory/Disk:

·         free -h

·         df -h

·         du -sh *

11) Networking basics

• Test connectivity: ping example.com (Ctrl+C to stop)

• Download: wget URL or curl -O URL

• Show IP info: ip a

• Remote login & copy:

·         ssh user@server

·         scp file.txt user@server:/home/user/

12) Package managers (install software)

• Ubuntu/Debian:

·         sudo apt update

·         sudo apt install git

·         sudo apt upgrade

• Fedora/RHEL: sudo dnf install <pkg>

• Arch: sudo pacman -S <pkg>

13) Shell scripting (your first automation)

hello.sh

#!/usr/bin/env bash

echo "Hello, $USER! Today is $(date +%A)."

Make executable & run:

chmod +x hello.sh

./hello.sh

Mini script with input, loop, and conditions

#!/usr/bin/env bash

read -p "Folder to back up: " SRC

DEST="$HOME/backups/$(date +%Y-%m-%d)"

mkdir -p "$DEST"

if [ -d "$SRC" ]; then

  cp -r "$SRC" "$DEST"

  echo "Backup done at $DEST"

else

  echo "Folder not found!"

fi

Concepts used: shebang, variables (SRC), input (read), if condition, -d (directory check), date, quoting paths with spaces.

14) Users, groups, and sudo

• Add user (admin action): sudo adduser ankit

• Add to group: sudo usermod -aG sudo ankit

• Change password: passwd

• sudo runs a command with admin privileges: sudo apt install tree

15) Environment basics

• Show environment vars: env, echo $PATH

• Add aliases/functions in ~/.bashrc or ~/.zshrc (then source ~/.bashrc)

·         echo 'alias ll="ls -alF"' >> ~/.bashrc

16) Open Source: values & licenses

• Open source means the source code is available to use, study, modify, and share.

• Core ideas (the “freedoms”):

1.   Use the software for any purpose.

2.   Study how it works (access to source).

3.   Modify it.

4.   Share copies (original or modified).

Popular licenses (simple view):

• MIT: very permissive; use anywhere, just keep the license notice.

• Apache-2.0: permissive + explicit patent protection.

• GPL-3.0: “copyleft”; if you distribute modified versions, you must keep it open under GPL as well.

Choosing a license (quick rule):

• Want maximum freedom for users (including closed-source use)? MIT/Apache.

• Want improvements to stay open? GPL.

Contributing to open source:

• Find a project on GitHub/GitLab → read CONTRIBUTING.md → fix a bug or docs → make a pull request.

17) Good habits & safety

• Tab-complete paths; use quotes for paths with spaces: "My Files"

• Read man pages: man ls (q to quit)

• Prefer rm -ri (interactive) for safety; keep regular backups.

• Use version control: git init, git add, git commit.

18) 30-minute practice lab (do this now)

1.   Create a playground:

2. mkdir -p ~/lab/linux101 && cd ~/lab/linux101

3.   Make files & folders:

4. mkdir src docs

5. echo "Hello Linux" > docs/readme.txt

6. cp docs/readme.txt src/hello.txt

7. ls -la

8.   Search & count:

9. grep -r "Hello" .

10. wc -l src/hello.txt

11.                     Permissions:

12. echo -e '#!/usr/bin/env bash\necho Linux!' > run.sh

13. chmod 755 run.sh

14. ./run.sh

15.                     Package install (Ubuntu example):

16. sudo apt update && sudo apt install tree

17. tree ~/lab/linux101

19) Quick cheat sheet

pwd                 # print current directory

ls -la              # list (all, long)

cd /path            # change directory

mkdir newdir        # make directory

cp src dst          # copy (add -r for folders)

mv old new          # move/rename

rm file             # remove (use -r for folders, -i to confirm)

cat/less file       # show file

grep "text" file    # search text

find . -name "*.py" # find files by pattern

chmod 755 file      # set permissions

top                 # live process view

df -h               # disk usage (drives)

du -sh *            # disk usage (folders)

ping example.com    # test network

wget/curl URL       # download

ssh user@host       # remote login

sudo apt install x  # install (Ubuntu/Debian)

Want this as a printable PDF or a slide deck?

Say the word and I’ll turn these notes into a nicely formatted PDF or PPT for your class.