Linux Directory Structure Reference Guide

Simple reference guide for Linux directories and their use

* AI Generated

Overview

The Linux filesystem follows a hierarchical structure defined by the Filesystem Hierarchy Standard (FHS). Understanding this structure is essential for system administration, software deployment, and general Linux usage.

Root Directory Structure

/ (Root Directory)

The top-level directory that contains all other directories and files in the system.

Essential System Directories

/bin - Essential User Binaries

• Purpose: Contains essential command-line utilities needed by all users
• Availability: Must be available even in single-user mode
• Examples: ls, cp, mv, cat, bash, grep
• Note: These are commands you’d expect to work on any Linux system

/sbin - System Binaries

• Purpose: Essential system administration commands
• Access: Typically used by root/administrators
• Examples: mount, umount, fsck, iptables, systemctl
• Note: “s” stands for “system” or “superuser”

/lib - Essential Libraries

• Purpose: Shared libraries required by programs in /bin and /sbin
• Contents: Dynamic linking libraries (.so files)
• Importance: Critical for system boot and basic functionality

User and Application Directories

/usr - User System Resources

Secondary hierarchy containing the majority of user utilities and applications.

Key subdirectories:

• /usr/bin - Non-essential user commands and applications
• /usr/sbin - Non-essential system administration binaries
• /usr/lib - Libraries for /usr/bin and /usr/sbin programs
• /usr/local - Local software installations (not from package manager)
• /usr/share - Architecture-independent shared data

/opt - Optional Software Packages

• Purpose: Self-contained third-party software packages
• Structure: Each package gets its own subdirectory (e.g., /opt/google/chrome)
• Use Cases:
  • Commercial software
  • Large application suites
  • Proprietary applications
  • Software that prefers to keep all files together
• Examples: Oracle Database, VMware, Google Chrome, custom enterprise applications

/home - User Home Directories

• Purpose: Personal directories for regular users
• Structure: /home/username
• Contents: User files, personal configurations, documents

/root - Root User Home

• Purpose: Home directory specifically for the root user
• Location: Separate from /home for security and availability reasons

Configuration and Data Directories

/etc - System Configuration

• Purpose: System-wide configuration files
• Format: Text-based configuration files
• Examples: /etc/passwd, /etc/hosts, /etc/apache2/, /etc/ssh/
• Scope: Affects entire system, not individual users

/var - Variable Data

• Purpose: Files that change during normal system operation
• Key subdirectories:
  • /var/log - System and application log files
  • /var/mail - User mailboxes
  • /var/tmp - Temporary files preserved between reboots
  • /var/lib - Application state data
  • /var/cache - Application cache data

Temporary and Runtime Directories

/tmp - Temporary Files

• Purpose: Temporary files for applications and users
• Cleanup: Often cleared on system reboot
• Access: World-writable with sticky bit set
• Usage: Short-term storage during program execution

Boot and Hardware Directories

/boot - Boot Files

• Purpose: Files required for system startup
• Contents: Kernel images, initial RAM disk, bootloader configuration
• Examples: vmlinuz, initrd.img, GRUB configuration

/dev - Device Files

• Purpose: Special files representing hardware devices
• Type: Character and block device files
• Examples: /dev/sda (hard drive), /dev/null, /dev/random
• Management: Usually managed automatically by udev

Virtual Filesystems

/proc - Process Information

• Purpose: Virtual filesystem exposing kernel and process information
• Contents: Process directories (numbered by PID), system information
• Examples: /proc/cpuinfo, /proc/meminfo, /proc/1/ (init process)
• Note: Files exist only in memory, not on disk

/sys - System Information

• Purpose: Virtual filesystem for modern kernel object information
• Contents: Hardware device information, kernel modules, power management
• Usage: Used by modern system management tools
• Note: More structured than /proc

Mount Point Directories

/mnt - Manual Mount Point

• Purpose: Temporary mount point for manually mounted filesystems
• Usage: System administrators mount filesystems here temporarily
• Examples: Mounting external drives for maintenance

/media - Removable Media

• Purpose: Automatic mount points for removable media
• Management: Usually handled by desktop environments
• Examples: /media/usb-drive, /media/cdrom

Quick Reference Summary

Best Practices for Students

1. Exploration: Use ls -la to explore directory contents and permissions
2. Documentation: Check man hier for detailed filesystem hierarchy information
3. Respect: Be cautious when working in system directories (especially as root)
4. Understanding: Learn the logic behind the structure - it makes navigation intuitive
5. Practice: Set up a virtual machine to safely explore the filesystem structure

Common Confusion Points

• /usr vs /usr/local: /usr is for package-managed software, /usr/local is for manually compiled/installed software
• /bin vs /usr/bin: /bin is for essential commands, /usr/bin is for additional user programs
• /tmp vs /var/tmp: /tmp may be cleared on reboot, /var/tmp should persist across reboots
• /opt vs /usr/local: Both for additional software, but /opt is for packaged applications, /usr/local follows standard hierarchy

This structure has evolved over decades and represents a balance between organization, tradition, and practical system administration needs.