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Chapter 3.1 - Introduction to the File System

Learning Objectives​

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

  • Understand what the Linux file system is
  • Explain the hierarchical structure
  • Distinguish between different file types
  • Understand absolute and relative paths

What is the File System?​

The Linux file system organizes data on the disk into files and directories. It follows a unique hierarchical structure with / (root) as the starting point.

Characteristics:

  • Hierarchical structure (tree)
  • A single starting point: /
  • Absolute and relative paths
  • Case-sensitive (uppercase/lowercase)

Why this Structure?​

Advantages of the Hierarchy​

Organization:

  • Clear separation of functions
  • Easy to navigate
  • Standardized (FHS - Filesystem Hierarchy Standard)

Security:

  • Permissions per directory
  • User isolation
  • System file protection

File Types​

Regular Files​

Files containing data:

  • Texts, images, executables, etc.
  • Identified by - in ls -l

Directories​

Containers of files:

  • Organize files
  • Identified by d in ls -l

Pointers to other files:

  • Similar to Windows shortcuts
  • Identified by l in ls -l

Devices​

Representations of hardware:

  • /dev/sda (disk)
  • /dev/tty (terminal)
  • Identified by b (block) or c (character)

Absolute vs Relative Paths​

Absolute Path​

Always starts with /:

/home/user1/documents/file.txt
/etc/passwd
/usr/bin/ls

Advantages:

  • Always valid from anywhere
  • Clear and explicit

Relative Path​

Relative to the current directory:

# If you are in /home/user1
documents/file.txt        # Relative
./documents/file.txt      # Same thing
../user2/documents/file.txt  # Parent then user2

Special symbols:

  • . : Current directory
  • .. : Parent directory
  • ~ : User's home directory

Standard Structure (FHS)​

Essential Directories​

Quick description:

  • /bin: Essential commands (ls, cp, mv)
  • /etc: System configuration
  • /home: User directories
  • /usr: Programs and libraries
  • /var: Logs, cache, variable data
  • /tmp: Temporary files

Basic Navigation​

Essential Commands​

# See where you are
pwd

# Change directory
cd /home/user1
cd ~              # Home
cd ..             # Parent
cd -              # Previous

# List files
ls                # Simple list
ls -l             # Details
ls -la            # All (including hidden)
ls -lh            # Human-readable sizes
ls -lt            # Sorted by date

# Create directories
mkdir my_repo
mkdir -p full/path  # Create parents if necessary

# Remove
rmdir empty_repo
rm -r repo        # Recursive

Summary​

In this chapter, you learned:

File System: Hierarchical organization of data
Structure: Tree with / as root
Types: Files, directories, links, devices
Paths: Absolute (/) vs relative (., .., ~)
FHS: Standard directory structure
Navigation: pwd, cd, ls, mkdir, rmdir

Next Steps​

Chapter 3.2: Directory Structure
Chapter 3.3: Navigation and Basic Commands

Chapter created on: December 2024