Chapter 4: File System & Navigation

Learning Objectives

By the end of this chapter, you will be able to:

• Understand the Linux file system hierarchy
• Navigate directories using cd, pwd, and ls
• Create and remove directories and files
• Differentiate between absolute and relative paths
• Use tab completion to work more efficiently
• Understand home directories and the ~ shortcut

Prerequisites

• Completed Part I: Foundations
• Have a working Linux installation with terminal access

The Linux File System Hierarchy

Unlike Windows, which uses drive letters (C:, D:, etc.), Linux uses a single unified directory tree starting at the root directory, represented by / (forward slash).

/ (root)
├── bin/        # Essential user binaries (ls, cp, cat, etc.)
├── boot/       # Boot loader files
├── dev/        # Device files
├── etc/        # Configuration files
├── home/       # User home directories
│   ├── student/
│   └── user/
├── lib/        # System libraries
├── media/      # Removable media mount points
├── mnt/        # Mount point for temporary filesystems
├── opt/        # Optional software packages
├── proc/       # Process and kernel information
├── root/       # Home directory for root user
├── run/        # Runtime data
├── sbin/       # System binaries
├── srv/        # Service data
├── sys/        # Kernel and hardware information
├── tmp/        # Temporary files
└── var/        # Variable data (logs, spool, etc.)

Key Directories to Remember

Essential Navigation Commands

pwd - Print Working Directory

Shows your current location in the file system.

$ pwd
/home/student

ls - List Directory Contents

Shows files and directories in your current location.

$ ls
Documents  Downloads  Music  Pictures  Videos

Common ls options:

$ ls -la
drwxr-xr-x 5 student student 4096 Jan 15 10:30 Documents
drwxr-xr-x 2 student student 4096 Jan 14 09:15 Downloads
-rw-r--r-- 1 student student  123 Jan 15 10:00 notes.txt

cd - Change Directory

Navigate to different directories.

cd           # Go to home directory (same as cd ~)
cd ..        # Go up one level (parent directory)
cd /         # Go to root directory
cd -         # Go to previous directory
cd ~/Music   # Go to Music subdirectory in home

Examples:

$ pwd
/home/student

$ cd /etc
$ pwd
/etc

$ cd ..
$ pwd
/

$ cd -
$ pwd
/etc

Paths: Absolute vs. Relative

Understanding paths is fundamental to Linux navigation.

Absolute Paths

Start from / (root) and specify the complete path.

cd /home/student/Documents
cd /etc/nginx
cd /var/log

When to use: When you want to be precise about the location, regardless of where you currently are.

Relative Paths

Start from your current directory (also called "working directory").

cd Documents           # Go into Documents in current directory
cd ../Pictures         # Go up one level, then into Pictures
cd ./Music/songs       # Explicit reference to current directory

Special path symbols:

Visual Example

/
└── home/
    └── student/
        ├── Documents/
        │   └── project.txt
        ├── Downloads/
        └── Pictures/

If you're in /home/student/Documents:

Creating and Removing Directories

mkdir - Make Directory

Create new directories.

mkdir project                    # Create single directory
mkdir -p a/b/c                  # Create nested directories (parents)
mkdir -p ~/linux-course/session{01..10}  # Create multiple directories

The -p flag is particularly useful:

• Creates parent directories if they don't exist
• Doesn't error if directory already exists

rmdir - Remove Directory

Remove empty directories only.

rmdir empty-folder

rm - Remove Files and Directories

Remove files and directories (use with caution!).

rm file.txt                     # Remove file (asks for confirmation)
rm -f file.txt                  # Force remove (no confirmation)
rm -r directory/                # Remove directory and contents
rm -rf directory/               # Force remove directory recursively

Warning: rm -rf is permanent. There's no recycle bin in the terminal!

Creating Files

touch - Create Empty File

Create an empty file or update timestamps.

touch notes.txt                 # Create new empty file
touch report.md todo.txt        # Create multiple files

Creating Files with Content

You'll learn more about text editors and redirection in Chapter 5, but here's a quick preview:

echo "Hello, Linux!" > hello.txt    # Create file with content
cat > newfile.txt << EOF
Line 1
Line 2
Line 3
EOF

Tab Completion: Your Best Friend

Tab completion saves time and prevents typos. Start typing a command or filename, then press Tab.

How It Works

$ cd Doc[TAB]          # Expands to: cd Documents
$ ls /hom[TAB]         # Expands to: ls /home/
$ cat note[TAB]        # Expands to: cat notes.txt

Multiple Matches

If multiple files match your prefix, press Tab twice to see all options:

$ cd Do[TAB][TAB]
Documents/  Downloads/

Tips for Tab Completion

1. Always use it - It prevents typos and saves keystrokes
2. Press Tab twice - If nothing happens, press again to see options
3. Works with commands too - Type cha[TAB] to get chattr, chacl, etc.
4. Handles paths - ~/Doc[TAB] → ~/Documents/

Hidden Files and Directories

In Linux, files starting with a dot (.) are hidden by default. They're not shown in regular ls output.

$ ls
Documents  Downloads  Music

$ ls -a
.  ..  .bashrc  .config  .gitconfig  Documents  Downloads  Music

Common hidden files:

Practical Examples

Example 1: Setting Up a Course Directory

# Start from home
cd ~

# Create course structure
mkdir -p linux-course/{session{01..10},exercises,notes}

# Navigate into session 01
cd linux-course/session01

# Create a notes file
touch notes.txt

# Go back to course root
cd ~/linux-course

# Verify structure
ls -R

Example 2: Exploring System Directories

# Look at what's in /etc
cd /etc
ls

# Find SSH configuration
cd ssh
ls -la

# Return home quickly
cd ~

Example 3: Cleaning Up Downloads

# Go to Downloads
cd ~/Downloads

# List files sorted by size (you'll learn this in Chapter 5)
ls -lhS

# Remove old files (be careful!)
rm old-file.zip

# Clean up empty directories
cd ..
rmdir Downloads/old-empty-folder

Summary

In this chapter, you learned:

• File System Structure: Linux uses a single tree starting at /
• Key Directories: /home (user files), /bin (programs), /etc (config)
• Navigation Commands:
  • pwd - Where am I?
  • ls - What's here?
  • cd - Go somewhere
• Paths: Absolute (from /) vs relative (from current directory)
• Special Symbols: . (current), .. (parent), ~ (home)
• Directory Management: mkdir, rmdir, rm -r
• Tab Completion: Always press Tab to save time and avoid typos

Chapter Quiz

Test your understanding of the Linux file system and navigation:

Exercises

Exercise 1: Directory Navigation

1. Open your terminal
2. Navigate to /etc
3. List the contents
4. Go to /var/log
5. Return to your home directory using a single command
6. Verify you're home with pwd

Exercise 2: Create Course Structure

Create this directory structure in your home folder:

~/linux-course/
├── session01/
├── session02/
├── session03/
└── exercises/
    ├── basic/
    └── advanced/

Exercise 3: File Creation Practice

1. Navigate to ~/linux-course/session01
2. Create an empty file called notes.txt
3. Go back to ~/linux-course
4. Use tab completion to navigate to session01/notes.txt

Exercise 4: Path Practice

Starting from /home/student, use relative paths to:

1. Go to /home/student/Documents
2. From there, go to /home/student/Pictures using only relative paths
3. Return to /home/student using the shortest command

Exercise 5: Exploration Challenge

1. Navigate to /usr/bin
2. Count how many executables are there (hint: ls | wc -l)
3. Find if python3 exists there (hint: ls python*)
4. Explore what's in /tmp

Expected Output

Exercise 1 Solution

$ cd /etc
$ ls
aiccu          cups           ld.so.cache   nsswitch.conf  udev
alias          dbus           libao.conf    opt            udisks2
...

$ cd /var/log
$ pwd
/var/log

$ cd ~
$ pwd
/home/student

Exercise 2 Solution

$ mkdir -p ~/linux-course/session{01..03}
$ mkdir -p ~/linux-course/exercises/{basic,advanced}
$ cd ~/linux-course
$ tree -L 2    # or use: find . -type d -maxdepth 2
.
├── exercises
│   ├── advanced
│   └── basic
├── session01
├── session02
└── session03

Exercise 3 Solution

$ cd ~/linux-course/session01
$ touch notes.txt
$ cd ~/linux-course
$ cd ses[TAB]    # Expands to session01
$ ls
notes.txt

Exercise 4 Solution

$ cd ~/linux-course/session01
$ cd ../../Pictures      # or: cd ../session02
$ cd ~                   # or: cd /home/student

Next Chapter

In Chapter 5, you'll learn CLI Fundamentals - viewing files, copying and moving, pipes, redirection, and wildcards. This will build on your navigation skills to make you truly productive in the terminal.