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Project 1: minitar - A Posix-Compatible Archive Utility

Source

This project was taken from CSCI 4061 Intro to Operating Systems at the University of Minnesota - Twin Cities [Fall 2024], taught by Jack Kolb.

📦 Starter Code

You can download the starter code here: proj1-code.zip

Save the starter code under your csci4061 directory, which should now look like this:

csci4061/
├── labs/
│   ├── lab01-code/
│   └── ...
└── projects/
    └── proj1-code/

✅ How to Succeed on This Project

  • Read the spec thoroughly. TAs may decline to help if you haven’t.
  • Understand the starter code. Know what each file does.
  • Test independently. Don’t rely solely on automated tests.
  • Expect bugs. Stay patient and persistent.
  • Start early. Avoid deadline pressure.
  • Ask questions publicly on Piazza. This helps everyone.
  • Know the late policy. No submissions accepted more than 48 hours late.

🧭 Introduction

In this project, you will implement a simplified version of the Unix tar utility called minitar. You’ll work with C and the stdio library to: - Practice file I/O - Explore systems programming techniques - Build a Posix-compliant archive tool

Your implementation will be able to: - Create and append to archives - Extract files - Interoperate with tar

💻 Makefile Commands

make                # Compile minitar
make clean          # Remove compiled files
make clean-tests    # Remove test output
make zip            # Create Gradescope zip
make test           # Run all test cases
make test testnum=5 # Run specific test

🧪 Manual Testing Advice

  • Use your own test cases
  • View archives using: 
    xxd test.tar | less
  • Use tar for interoperability comparison
  • Install xxd in Docker: 
    apt update
apt install xxd

🧰 Starter Code Files

File Purpose Notes
Makefile Build/tests Do not modify
file_list.h / file_list.c Linked list support Do not modify
minitar.h Archive headers Do not modify
minitar.c Archive operations EDIT THIS
minitar_main.c CLI logic EDIT THIS
testius Test runner Do not modify
test_cases/ Sample inputs Do not modify

Only modify the files marked as EDIT.

📦 Archive Format Overview

  • Each archive is made of 512-byte blocks
  • Each file: 1 header block + content blocks
  • Ends with two zero blocks

tar_header Struct

Defined in minitar.h, it uses octal-encoded strings for numeric fields.

char size[12];  // octal, null-terminated string

Use fill_tar_header() to generate headers.

🚀 Archive Operations

Create

./minitar -c -f archive.tar file1 file2
- Write header and data for each file - Add two-block footer

Append

./minitar -a -f archive.tar newfile
- Remove footer with remove_trailing_bytes() - Append new headers/data - Add new footer

List

./minitar -t -f archive.tar
- Print name of each file in archive - Stop when footer blocks are reached

Update

./minitar -u -f archive.tar existingfile
- Like append, but must already exist in archive - Error message if not: 
Error: One or more of the specified files is not already present in archive.

Extract

./minitar -x -f archive.tar
- Write out each member file - Only extract latest version if duplicates exist

💡 Tips & Assumptions

  • No nested directory support
  • Use high-level I/O (fopen, not open)
  • Use memset(), fseek(), ftell()
  • Leverage fill_tar_header() and file_list utilities

Useful C Functions

  • fread(), fwrite()
  • ftell(), fseek()
  • sscanf() for octal parsing
  • perror() for error reporting

🧠 Strategy & Hints

  • Reuse logic between operations
  • Write helpers for block iteration
  • Start early, debug often, test manually
  • Avoid mixing fopen() and open()

📌 Summary

This project is your first big opportunity to apply systems-level thinking and build a utility that mirrors a well-known Unix tool. You'll practice file I/O, struct management, and command-line parsing — and develop habits that will serve you in all future OS coursework.

Ready to begin? Download the starter code and get coding!