ext2 File System Shell (Linux-Commands)

An interactive shell built from scratch in C to navigate and inspect an `ext2` file system image, demonstrating a deep understanding of low-level file system architecture and direct disk access.

About The Project

This project is an implementation of an interactive shell designed to manipulate and analyze ext2 file system images, which are based on the Berkley Fast File System (FFS). The primary goal was to develop a toolset capable of navigating the internal structure of a disk image, allowing for operations like file listing, directory traversal, and metadata inspection by directly accessing disk blocks.

The entire project was developed in C, using the data structures defined by the ext2 system to interpret raw disk data without relying on the host operating system's file system drivers.

Key Features

The shell provides a set of essential commands to explore the ext2 image:

• ls: Lists all files and subdirectories in the current directory, reading directory entries from data blocks.
• cd: Navigates through the directory hierarchy by resolving directory names to their corresponding inodes.
• stat: Displays detailed metadata for any given file or directory, including permissions, size, timestamps, and data block pointers stored in its inode.
• find: Performs a recursive search from the current directory to map and display the entire underlying file hierarchy.
• sb: Reads and displays global metadata from the filesystem's superblock, such as total blocks, inode counts, and block size.

Tech Stack

• C Programming Language
• ext2 File System Principles
• Direct Disk I/O Operations

Getting Started

The shell is a single translation unit and needs no build system. It requires a Linux environment, since it uses the byte-order helpers from <endian.h>.

1. Clone the repo

   git clone https://github.com/Gronoxx/Linux-Commands.git
   cd Linux-Commands

2. Compile

   gcc -Wall -o ext-shell main.c

3. Run against a filesystem image

   ./ext-shell imagem.img

Two ready-to-use ext2 images ship with the repository: imagem.img (10 MB) and imagem2.img (1 MB). Once the shell starts, type ls, cd, stat, find or sb.

The full write-up for the assignment is included as Relatório SO TP3.pdf (in Portuguese).

My Contribution

This project was developed in a team of three for the Operating Systems course. Due to unforeseen circumstances with another team member, our group was formed at the last minute to tackle this complex assignment.

In this challenging context, I collaborated equally on all fronts of the project, from design to implementation. My key contributions included:

• Designing the in-memory data structures for the superblock, group descriptors, and inodes.
• Implementing the logic for the stat and recursive find commands, which required deep traversal of directory entries and inodes.
• Developing the core functions for reading data directly from disk blocks at specific offsets.
• Debugging low-level memory management issues and disk read errors.

Course Context

This was the final project for the Operating Systems (DCC605) course at Universidade Federal de Minas Gerais (UFMG). The project was instrumental in providing a practical understanding of modern file system concepts like inodes, block allocation, and directory structures.