Understanding Linux Filesystems: Inodes, Directory Structure, and Links Explained

1 Introduction

We briefly look at Linux system disks, directories, and files.

2 Linux Filesystem

In Linux, all resources managed by the operating system—network interfaces, disks, printers, I/O devices, regular files, or directories—are treated as files.

This reflects the Unix philosophy that “everything is a file,” including hardware devices, which are represented as device files.

Linux supports five file types, as shown below:

3 Linux Directory Structure

The Linux filesystem hierarchy resembles an inverted tree, with the root directory at the top.

Common directory explanations:

4 What is an inode

An inode is a crucial concept for understanding Unix/Linux filesystems and disk storage.

Understanding inodes starts with file storage.

Files are stored on disks in sectors (512 bytes each).

The OS reads multiple sectors at once as a block, typically 4 KB (8 sectors).

The metadata about a file—owner, timestamps, size, etc.—is stored in an inode (index node).

Each file has a corresponding inode containing its information.

Linux uses the inode table to map a file’s logical structure to its physical blocks.

Each inode is a 64‑byte record containing size, owner, permissions, type, and a disk address table with 13 block numbers that point to the file’s data blocks.

When a file is accessed, the filesystem looks up the filename in the current directory, obtains the inode number, and uses the inode’s address table to assemble the file’s logical structure from its scattered blocks.

5 Hard Links and Soft Links

Hard link: a pointer to the same inode; creating a hard link increments the link count.

Limitations: cannot link across different filesystems; only superuser can create hard links to directories.

Soft (symbolic) link: a separate inode that stores the path to the target file, allowing cross‑filesystem links and greater flexibility.

Limitations: if the target moves, the link breaks; it consumes extra inode space for the path.

In practice, soft links are used more often. Key differences:

Hard links cannot cross partitions; soft links can.

Hard links point to the same inode; soft links create a new inode.

Deleting a hard link does not delete the original file; deleting a soft link does not affect the target file.