The Hierarchical Tree Structure in Linux File System

The Linux file system is organized as a single hierarchical tree, where:

• The root of the tree is represented by /.
• Every file, directory, device, and resource is located somewhere within this tree.
• Each item in the system has a unique path starting from / that identifies its location.

This structure allows Linux to maintain a clear, organized, and scalable file system, where everything is part of a single, unified directory tree.

/
├── bin/
├── boot/
├── dev/
├── etc/
├── home/
│   ├── user1/
│   ├── user2/
│   └── ...
├── lib/
├── media/
├── mnt/
├── opt/
├── proc/
├── root/
├── sbin/
├── tmp/
├── usr/
└── var/

• Absolute Path:

  • Always starts from /
  • Describes the complete location of a file or directory in the system.
  • Examples:
    • /etc/passwd
    • /home/user1/documents/resume.pdf

• Relative Path:

  • Starts from the current working directory.
  • For example, if you are in /home/user1 and want to access documents/resume.pdf, you can reference it as:
    • documents/resume.pdf

The file system resembles an inverted tree:

• The root (/) is the top of the tree.
• Directories branch out from the root (branches), and files are like leaves.

Key Directories in the Linux File System

The Linux file system is organized in a standardized way. Each major directory has a specific purpose. Here’s an overview of the most important directories:

• / – Root Directory

  • The starting point of the file system hierarchy. Everything in the system is organized under this directory.

• /bin – Essential User Binaries

• Contains essential command-line binaries (programs) that are required for basic system functionality. Examples: ls, cp, mv, bash, cat.

• /sbin – System Binaries

  • Contains system administration binaries that are typically used by the system or by the root user. Examples: fsck, reboot, ifconfig.

• /etc – Configuration Files

  • Contains system-wide configuration files and scripts. Examples:
    • /etc/passwd – User account information.
    • /etc/fstab – Filesystem mount points.

• /home – User Home Directories

  • Contains personal directories for each user. For example: /home/user1/ , /home/user2/
  • Each user’s files, configurations, and data are stored here.

• /root – Root User Home Directory

  • The home directory for the root user (system administrator).
  • Equivalent to /home/root for the superuser.

• /var – Variable Files

  • Contains files that are expected to grow, such as:
    • Logs (/var/log).
    • Spools (/var/spool).
    • Temporary mail files, caches, etc.

• /usr – User Programs and Data

  • Contains user-installed programs and their data. Subdirectories include:
    • /usr/bin – Non-essential user binaries.
    • /usr/lib – Libraries.
    • /usr/share – Shared data like documentation, icons, and locale files.
    • /usr/include – Header files for development (e.g., C libraries).

• /lib – Essential Shared Libraries

  • Contains shared libraries needed for programs in /bin and /sbin to run.
    • For example: libc.so.6.

• /dev – Device Files

  • Contains files that represent devices on the system (everything is a file in Linux). Examples:
    • /dev/sda – Hard disk.
    • /dev/tty – Terminals.
    • /dev/null – Discard output.

• /proc – Virtual Filesystem for Process and Kernel Information

  • A pseudo-filesystem that provides dynamic information about running processes and the kernel. Examples:
    • /proc/cpuinfo
    • /proc/meminfo
    • /proc/1234/ (information about process with PID 1234).

• /tmp – Temporary Files

  • Used for storing temporary files created by users or applications. Files here are usually deleted upon system reboot.

• /media and /mnt – Mount Points

  • /media – Mount points for removable devices (e.g., USB drives, CD-ROMs).
  • /mnt – A general mount point for mounting temporary filesystems.

• /opt – Optional Software

  • Used for installing add-on application software packages.

Directory	Purpose
/	Root directory – top of the file system hierarchy.
/bin	Essential binaries for all users.
/sbin	System binaries for administrative tasks.
/etc	Configuration files.
/home	User home directories.
/root	Root user's home directory.
/var	Variable data: logs, spools.
/usr	User programs and libraries.
/lib	Essential shared libraries.
/dev	Device files.
/proc	Process and kernel information.
/tmp	Temporary files.
/media	Mount points for removable media.
/mnt	Temporary mount point.
/opt	Optional software packages.