Linux File System Structure Explained: Root And Directories

Linux File System Structure

The Linux file system is a hierarchical, tree-like structure defined by the Filesystem Hierarchy Standard (FHS), with a single root directory represented by a forward slash (/). All files, directories, and even hardware devices are represented as files under this single unified structure.

Essential Features

• All data and devices (such as hard disks, printers, and processes) are handled as files under Linux, which makes system interaction easier.

• Case Sensitivity: “File1” and “file1” are regarded as separate files because filenames are case-sensitive.

• Hierarchical Structure: Every directory in the system branches out of the root (/) directory, which is where the system begins.

• Mount Points: In the primary hierarchy, existing directories (mount points) can have additional file systems, partitions, or network shares linked to them.

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File system components in Linux

Virtual File System (VFS)

The Linux kernel and the underlying file systems (such as ext4 or XFS) are separated by an abstraction layer called the VFS.

No matter the underlying hardware, you may use the same cp or mv commands to the VFS. Because it serves as a “translator,” the kernel may read and write data without having to be familiar with the intricate technical specifics of each type of file system.

Inodes (Index Nodes)

A filename is merely a label in Linux. The Inode is the “soul” of a file. Each directory and file has a distinct inode number that contains the file’s metadata, such as:

• File type and size.
• Permissions for the owner and group (Read/Write/Execute).
• Creation, access, and modification timestamps.
• References to the disk’s actual data chunks.

Important Note: The filename is not stored in the inode. The Directory Entry contains the filename.

Superblocks

The “master record” of the whole file system is the Superblock. It includes the disk partition’s high-level metadata. The OS won’t be able to load the file system if the Superblock is corrupted. It keeps:

• The file system’s overall size.
• The quantity of accessible free blocks.
• The type of file system (ext4, for example).
• The file system’s state (clean or unclean).

The Superblock is so important that Linux typically maintains many backup copies of it on the drive.

Data Blocks

The real “storage bins” on your physical drive are called data blocks. Your files’ contents such as the text in a document, the code in a script, or the pixels in a picture are stored here.

• Blocks often have a fixed size, typically 4KB.
• The Inode offers a map of all the many blocks where the data in a file is dispersed if the file is greater than one block.

Directory Entries (Dentries)

In essence, a directory is basically a unique file with a list of filenames and the Inode numbers that correspond to them. when attempting to open a picture.jpg, Linux searches for that name in the Dentry, locates Inode #12345, and then visits the Inode to determine the location of the actual data blocks.

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The root directory(/)

The foundation of the entire file system is the root directory. This slash is where all of your computer’s files, devices, and folders are located. If the file system were an upsidae-down tree, / would be the trunk from which all other branches emerge.

Linux file directory structure

To keep the system organized, Linux follows the Filesystem Hierarchy Standard (FHS). Here is what each major directory actually does:

/bin – Essential User Binaries

• Contains essential command binaries that need to be available in single-user mode (like ls, cp, and grep).

Examples include:

• ls (list files)
• Cp (copy files)
• Mv (move files)
• Cat (view file content)
• Echo

These commands must be accessible even when the system is in rescue mode.

/sbin – System Binaries

• Similar to /bin, but contains commands intended for the system administrator (root) for system maintenance (like iptables or reboot).

Examples:

• Shutdown
• Reboot
• Fsck (file system check)
• Ifconfig / ip

These tools are critical for system maintenance and repair.

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/etc– Configuration Files

• This is the “control panel” of your Linux system. It contains all the system-wide configuration files (e.g., /etc/passwd for users or /etc/fstab for drives). It does not store programs, only text files that define how services behave.

Examples:

• /etc/passwd – user accounts
• /etc/fstab – disk mount rules
• /etc/hostname – system name
• /etc/network – network settings

Almost every system customization involves editing files in /etc.

/home (User Directories)

• This is where users store their personal documents, photos, and settings. Each user gets a subfolder (e.g., /home/jane).

Each user has their own folder:

• /home/hhh
• /home/aaa

This directory contains:

• Documents
• Downloads
• Desktop files
• User settings

It is safe to back up or reinstall the OS while keeping /home intact.

/var (Variable Files)

• Contains files that are expected to grow in size over time, such as system logs (/var/log), databases, and email spools.

It includes:

• Log files (/var/log)
• Mail files
• Printer queues
• Database files
• Cache files

If /var fills up, the system may crash or services may fail.

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/usr (User Programs)

• Historically stood for “Unix User Resources.” It contains the majority of user utilities and applications. It has its own /usr/bin and /usr/sbin for non-essential commands.

It contains:

• /usr/bin – user commands
• /usr/sbin – admin commands
• /usr/lib – libraries
• /usr/share – documentation

This is usually the largest directory on the system.

/tmp (Temporary Files)

• A place for applications to store temporary data. These files are usually deleted when you reboot.

Files in /tmp:

• Can be deleted anytime
• Are usually removed on reboot
• Should not store important data

It is often stored in RAM for faster performance.

/boot (Boot Loader Files):

• Contains everything needed to boot the system, including the Linux Kernel and the GRUB bootloader configuration.

Includes:

• Linux kernel (vmlinuz)
• initramfs
• GRUB configuration

Without /boot, the system cannot start.

/dev (Device Files)

• In Linux, hardware is represented as files. Your hard drive might be /dev/sda, and your keyboard or mouse also has a file representation here.

Examples:

• /dev/sda – hard disk
• /dev/tty – terminals
• /dev/null – discard output

Linux treats devices as files, allowing programs to interact with hardware easily.

/proc (Process Information)

• This is a “virtual” file system. It doesn’t exist on your disk; it exists in memory. It contains information about running processes and system resources (like CPU info).

It contains live system information:

• CPU details
• Memory usage
• Process status

Example:

cat /proc/cpuinfo

This shows real-time CPU data.

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File system types in linux

When you format a partition in Linux, you choose a “file system” which determines how data is indexed and retrieved.

File System	Best For	Key Features
ext4	General Use	The “standard” Linux file system. Extremely stable, reliable, and supports huge file sizes.
XFS	High Performance	Excellent for large-scale servers and handling massive files or high-concurrency workloads.
Btrfs	Advanced Users	Uses “Copy-on-Write.” Supports snapshots (like system restore points) and easy drive pooling.

Mounting and Unmounting

In Linux, connecting a storage device (like a USB drive or a second hard drive) to the file tree is called Mounting.

Mounting a Drive

To access a partition, you must “mount” it to a specific directory (a mount point).

Example:

bash

sudo mount /dev/sdb1 /mnt

Now, if you navigate to /mnt/my_usb, you are actually looking inside your USB drive.

Unmounting a Drive

Before unplugging a device, you must unmount it to ensure all data is written and nothing is corrupted.

Example:

bash

sudo umount /mnt/my_usb

• This safely detaches the disk.
• Never remove storage without unmounting, or data corruption may occur.
• The command is umount (no “n” after the “u”), which is a common typo for beginners!

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Automatic Mounting (fstab)

Linux uses /etc/fstab to mount disks automatically at boot.

Example entry:

ini

UUID=xxxx /data ext4 defaults 0 2

This ensures the disk always mounts on startup.

How to Check Your Current Structure

If you want to see how your own system is currently mapped out, run this command in your terminal:

lsblk (List Block Devices) or df -h (Disk Free – Human Readable).

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