Day 1 — File Structure: Windows vs Linux#

Goal: Understand how files are organized on Linux vs Windows so you never get confused about “where my file went” or “why can’t Python find my data.”

The Big Picture#

On Windows, your files live under drive letters:

C:\Users\alice\Documents\project\data.csv
D:\backup\photos\

On Linux, everything starts from a single root /:

/home/alice/projects/data.csv
/tmp/scratch.txt

There are no drive letters on Linux. Every file on the entire system hangs off /.

🧠 Knowledge Check#

Q1: In Linux, what is the equivalent of the C:\ drive in Windows?

• A) /home/
• B) / (root)
• C) ~
• D) /drive/c/

Linux Directory Tree — What Lives Where#

/                        ← root: the top of everything
├── home/                ← all user home directories
│   ├── alice/           ← Alice's personal files (also written as ~)
│   └── bob/             ← Bob's personal files
├── etc/                 ← system configuration files
├── usr/                 ← installed software
│   ├── bin/             ← most programs you run (python3, git, ls)
│   └── lib/             ← shared libraries
├── bin/                 ← essential system commands
├── tmp/                 ← temporary files (wiped on reboot!)
├── var/                 ← variable data (logs, databases)
│   └── log/             ← system logs
├── opt/                 ← optional third-party software
├── root/                ← home directory of the root (admin) user
├── proc/                ← virtual: info about running processes
├── dev/                 ← device files (disks, terminals)
└── mnt/                 ← mount points (WSL: Windows drives here)
    └── c/               ← (WSL only) your Windows C: drive

Key Directories You Should Know#

/home/yourname (a.k.a. ~)#

This is your space. You own everything here. No sudo needed.

# These are all the same:
cd ~
cd $HOME
cd /home/yourname

# Check:
echo $HOME
# /home/alice

What you’ll find in your home:

ls -la ~
# .bashrc         ← your shell config (runs every time you open a terminal)
# .gitconfig      ← your git settings
# .ssh/           ← your SSH keys (for GitHub, servers)
# .local/         ← user-installed programs (uv lives here)

Important: Files starting with . are hidden. Use ls -a to see them.

/tmp — Temporary Files#

# Anything here is deleted when you reboot
echo "scratch work" > /tmp/notes.txt
# After reboot → gone

Use it for: throwaway downloads, test files, temporary processing. Never use it for: your actual project files!

/usr/bin — Where Programs Live#

which python3     # /usr/bin/python3
which git         # /usr/bin/git
which ls          # /usr/bin/ls

When you install a program with sudo apt install, its executable usually ends up here.

/etc — System Configuration#

cat /etc/hostname     # your machine's name
cat /etc/hosts        # local DNS (IP-to-name mappings)
cat /etc/passwd       # list of all users (not actual passwords!)

You’ll rarely edit these, but you’ll read them when debugging.

🧠 Knowledge Check#

Q1: Where do your personal files live on Linux?

• A) /tmp
• B) /usr/bin
• C) /home/yourname (or ~)
• D) /etc

Q2: Why should you avoid storing project files in /tmp?

• A) Because they are public to everyone on the internet
• B) Because /tmp is strictly for system configuration files
• C) Because files in /tmp are deleted automatically when the system reboots
• D) Because /tmp limits file size to 1MB

Windows vs Linux — Side by Side#

WSL2: Two Filesystems on One Machine#

If you are on Windows using WSL2, there are two separate filesystems:

Windows filesystem:      C:\Users\alice\Documents\
Linux filesystem:        /home/alice/projects/

They can see each other:

# From Linux → access Windows files:
ls /mnt/c/Users/alice/Documents/

# From Windows → access Linux files:
# Open File Explorer → type \\wsl$\Ubuntu\home\alice\ in address bar

⚠️ Golden Rule: Keep your project files in /home/you/, NOT in /mnt/c/. Working across the filesystem boundary (/mnt/c/) is up to 10x slower and causes permission headaches.

🧠 Knowledge Check#

Q1: You are using WSL2. Where is the best place to create your new Python project?

• A) C:\Users\YourName\Documents\project
• B) /mnt/c/Users/YourName/projects
• C) /home/yourname/projects
• D) /tmp/projects

Case Sensitivity — A Silent Bug Factory#

# On Linux, these are THREE different files:
data.csv
Data.csv
DATA.CSV

# On Windows, they are all THE SAME file!

Why this bites you:

• You name a Python module MyUtils.py on Windows → works fine.
• Push to GitHub → your teammate on Linux does import myutils → ModuleNotFoundError.

Rule: Always use lowercase with hyphens or underscores: my-data.csv, train_model.py.

Line Endings — LF vs CRLF#

When you press Enter in a file:

• Linux inserts \n (LF = Line Feed)
• Windows inserts \r\n (CRLF = Carriage Return + Line Feed)

What goes wrong:

# A script written on Windows, run on Linux:
./setup.sh
# /bin/bash^M: bad interpreter
# The ^M is the invisible \r that Windows added

Fix:

# Convert Windows line endings to Linux:
sed -i 's/\r//' setup.sh

# Or use dos2unix:
sudo apt install dos2unix -y
dos2unix setup.sh

Prevent it with Git:

git config --global core.autocrlf input
# This tells Git: convert CRLF → LF on commit, keep LF on checkout

File Permissions#

Linux has a permission system that Windows doesn’t have:

ls -la
# -rwxr-xr-x  1 alice alice 1234 Jan 1 script.sh
#  |||
#  ||└── others can: read + execute
#  |└─── group can: read + execute  
#  └──── owner can: read + write + execute

Three permissions: read, write, execute. Three levels: owner, group, others.

The one you will hit:

./my-script.sh
# Permission denied

# Fix:
chmod +x my-script.sh
./my-script.sh   # works now

Q&A#

cd ~/projects        # same as cd /home/alice/projects
ls ~/.ssh            # same as ls /home/alice/.ssh

Exercises#

Exercise 1: Explore the filesystem

Run each command and note what it shows:

ls /
ls /home/
ls -la ~
cat /etc/hostname

Exercise 2: Find where programs live

which python3
which git
which ls
which uv

/usr/bin/python3
/usr/bin/git
/usr/bin/ls
/home/yourname/.local/bin/uv

Exercise 3: Case sensitivity test

cd /tmp
touch test.txt Test.txt TEST.TXT
ls test* Test* TEST*

rm /tmp/test.txt /tmp/Test.txt /tmp/TEST.TXT

Exercise 4: Line endings

# Create a file with Windows-style line endings:
printf "line1\r\nline2\r\nline3\r\n" > /tmp/windows-file.txt

# Check for \r characters:
cat -v /tmp/windows-file.txt
# You should see ^M at the end of each line

# Fix it:
sed -i 's/\r//' /tmp/windows-file.txt
cat -v /tmp/windows-file.txt
# No more ^M

Exercise 5: MCQ practice

Q1: What is the Linux equivalent of C:\Users\bob\Desktop\?

• A) /Users/bob/Desktop/
• B) /home/bob/Desktop/
• C) C:/Users/bob/Desktop/
• D) /mnt/bob/Desktop/

Q2: You save a file as Config.yaml on Windows and push to GitHub. Your teammate on Linux opens config.yaml. What happens?

• A) Works fine
• B) FileNotFoundError — Linux sees them as different files
• C) Git renames it automatically
• D) The file opens but is empty

Q3: Where should WSL2 project files live for best performance?

• A) C:\Users\you\projects\
• B) /mnt/c/Users/you/projects/
• C) /home/you/projects/
• D) /tmp/projects/