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Mellivora OS

Release License Platform Language

A bare-metal 32-bit x86 operating system written in NASM assembly.

Mellivora OS is a from-scratch hobby OS that boots on real x86 hardware or in QEMU. It includes a custom HBFS v3 filesystem with permissions and xattr, ring 3 user-mode execution, a DOS-inspired interactive shell with POSIX features, 182 syscalls, priority-based preemptive scheduling with per-task fd isolation, POSIX signals with a W^X trampoline, a VFS abstraction layer, AHCI SATA and Intel e1000 NIC drivers, a GDB remote stub, compositor surface IPC, an in-OS Tiny C Compiler, a package manager, 231 assembly programs, and 31 bundled samples (C, Perl, and BASIC).

New to the project? Start with the Installation Guide, then try the Tutorial or browse the Technical Reference.

🦡 At a Glance

  • Boot path: BIOS 3-stage boot or UEFI (gnu-efi PE32+) into 32-bit protected mode; optional x86-64 long-mode path
  • Userland: 90+ shell commands, 231 assembly programs, and 31 bundled samples (C, Perl, and BASIC)
  • Core pieces: HBFS v3 filesystem + VFS layer, ELF32 loader, buddy PMM allocator, serial/VGA/ATA drivers
  • Developer-ready: API docs, programming guide, regression tests, release packaging, and hbpkg package manager

✨ Features

Kernel & Architecture

  • 32-bit protected mode with flat memory model; optional x86-64 long-mode path (make 64bit)
  • UEFI boot — boot/uefi_loader.efi (gnu-efi PE32+) for UEFI firmware; make uefi / make run-uefi
  • Ring 0 / Ring 3 privilege separation — programs run in user mode
  • 182 syscalls via INT 0x80 — v10 adds dup/pipe2/mmap/mprotect/clock_gettime/surfaces; v11 adds sigaction/sigreturn/alarm/xattr; v12.0 adds full POSIX session/uid/signal/timer/termios set; v12.1 adds per-task errno (SYS_GETERRNO)
  • Virtual filesystem (VFS) — unified open/read/write/stat/readdir front-end; backends: HBFS (/), procfs (/proc), devfs (/dev), tmpfs (/tmp)
  • Priority-based preemptive scheduler — 4 priority levels (HIGH/NORMAL/LOW/IDLE), 128 concurrent ring-3 tasks; blocking waitpid
  • Per-task fd isolation (v12.1) — each task has a private 4 KB fd table page; no cross-task aliasing
  • POSIX-style signals — SIGINT, SIGKILL, SIGTERM, SIGTSTP, SIGCONT, SIGUSR1/2, SIGALRM, SIGCHLD; W^X sigreturn trampoline at 0x1FFFF000
  • Per-task errno (v12.1) — TCB_ERRNO in the TCB; read via SYS_GETERRNO
  • Process groups — PGID and SID support for job control
  • ELF32 loader — supports flat binaries and ELF executables
  • Physical memory manager with buddy allocator (order 0–11; malloc/free/realloc for user programs)
  • VBE/BGA graphics driver — high-resolution framebuffer modes (640×480, 800×600, 1024×768 at 32 bpp) with double buffering
  • Compositor surface IPC — kernel-managed pixel buffers with z-order and dirty-rect compositing (SYS_SURFACE_CREATE/COMMIT/DESTROY/MOVE/RESIZE)
  • Three-stage BIOS boot: MBR → Stage 2 (A20, memory map, protected mode) → Kernel

Ratel Init System

  • Sequential hardware initialization — VGA, PIC, IDT, PIT, keyboard, PMM, ATA, serial, TSS, scheduler, IPC, networking, e1000 NIC, paging, mouse, SB16, VBE, PCI, AC'97, ATA DMA, VirtIO, AHCI SATA, GDB stub
  • Filesystem mount — HBFS detection, validation, and auto-format
  • Shell handoff — drops into HB Lair interactive prompt after init completes

HB Lair Shell (v3.0)

  • 90+ built-in shell commands with aliases: file management, text processing, system info, process control
  • Tab completion, command history (128 entries), Ctrl+C hard-abort with proper cleanup
  • Enhanced line editing — Ctrl+A/E (home/end), Ctrl+U (kill line), Ctrl+W (delete word), Ctrl+L (clear+redraw)
  • Process management — ps, jobs, kill, bg, fg, nice for task control
  • Pipes, redirection, and chaining — |, >, >>, <, &&, and || for shell workflows
  • Alias system — define custom command shortcuts
  • 32 environment variables with $VAR expansion and $(cmd) command substitution, $((expr)) arithmetic expansion
  • Batch scripting — execute .bat files with sequential command processing
  • source / . — execute scripts in current shell context
  • PATH-based program search — run programs from any directory
  • Full path support — cat /docs/readme, run /bin/hello, diff /docs/a /docs/b
  • Multi-level subdirectories — up to 16 levels deep with cd, mkdir, pwd

HBFS Filesystem (v3)

  • Honey Badger File System v3 — custom filesystem with 4 KB blocks and write-ahead journal
  • 455 entries per root directory, 224 entries per subdirectory (288-byte entries, 253-char max filename)
  • File types: text, executable, directory, batch script
  • File permissions — Unix-style 12-bit mode (HBFS_DE_MODE); owner/group/other rwx enforced by hbfs_check_permission
  • Extended attributes — per-file xattr block; hbfs_xattr_get / hbfs_xattr_set kernel API
  • Feature flags — superblock HBFS_SB_FEATURES: journal, xattr, permissions
  • VFS integration — accessed via the VFS layer; raw fd_open / fd_read / fd_write still available
  • File descriptors: open/read/write/close/seek (8 legacy FDs; 64 VFS FDs)
  • Wildcards: * and ? pattern matching in del and copy

Drivers

  • VGA text mode (80×25, 16 colors)
  • PS/2 keyboard with shift, ctrl, and special key support
  • PS/2 mouse — 3-byte packet, IRQ12, cursor tracking
  • ATA PIO disk with LBA48 addressing
  • ATA Bus Master DMA — Intel PIIX3/4 IDE controller, PRD-based DMA reads
  • AHCI SATA (v11) — polling-mode SATA driver; auto-detected via PCI; falls back to ATA PIO
  • PIT timer at 100 Hz
  • PC speaker for sound/music
  • Sound Blaster 16 ISA DMA PCM playback
  • AC'97 audio — Intel ICH2/3/4 PCI DMA playback
  • Serial port (COM1 at 115200 baud) for debug output and GDB remote stub
  • Intel e1000 NIC (v11) — 82540EM, 16-entry TX ring / 32-entry RX ring; Ctrl+Alt+G for GDB breakpoint
  • RTC real-time clock for date/time
  • PCI bus — enumeration (buses 0–7), 64-entry device table
  • VirtIO PCI legacy — virtio-blk (block) and virtio-net (network)
  • GDB remote stub (v11) — RSP protocol over COM1; supports registers, memory, continue, step, breakpoints

Programs (231 assembly + 31 bundled samples)

  • Games (31): Snake, Tetris, Minesweeper, Galaga, Pac-Man, Game of Life, Maze, Kingdom, Outbreak, Neurovault, Blackjack, Rogue, Solitaire, Breakout, Raycaster, Robot Town, and more
  • HBU (Honey Badger Utilities): grep, sort, sed, awk, tr, wc, cut, head, tail, diff, find, uniq, rev, paste, xargs, tar, nm, and more
  • Tools: Text editor, hex viewer, file pager (more/pager), CSV viewer, dual-pane file manager (burrow), top process monitor
  • Demos: Mandelbrot/Julia renderers, plasma effect, VBE sprite blit, rotating cube, banner, colors, Doom fire effect
  • Languages: TCC (Tiny C Compiler), BASIC interpreter (basic + basicc compiler), Brainfuck interpreter, Perl interpreter, Forth interpreter
  • Network tools: ping, wget, nc, ftp, telnet, irc, gopher, dig, traceroute, whois, daytime
  • Daily-driver suite (new): tutorial, pkginfo, meminfo, journal, bcal, theme, tag, histgrep, bnotify, mkprog, dnslook, play, nim, plasma, tldr, todo, pomodoro, morse, wiki, color, stopwatch, countdown, passgen, dice, coin, tip, roll, pick, reverse, upper, lower, countc
  • API Libraries: 17 reusable .inc libraries in programs/lib/ (string, I/O, math, VGA, memory, data, net, GUI, VBE, font, audio, highscore, and more)
  • Samples: 17 C programs + 9 Perl scripts + 5 BASIC scripts in /samples

🚀 Quick Start

Prerequisites

# Debian/Ubuntu
sudo apt install nasm qemu-system-x86 make python3

# Fedora
sudo dnf install nasm qemu-system-x86 make python3

# Arch Linux
sudo pacman -S nasm qemu-full make python

# macOS
brew install nasm qemu make python3

Build & Run

git clone https://github.com/James-HoneyBadger/Mellivora_OS.git
cd Mellivora_OS
make full      # Build everything
make run       # Launch in QEMU

That's it. You'll see the HB Lair boot banner and a shell prompt:

Lair:/>

Type help to see all available commands, or just start exploring:

Lair:/> dir                    # List files and directories
Lair:/> cd games               # Enter the games directory
Lair:/> snake                  # Play Snake!
Lair:/> cd /                   # Back to root
Lair:/> cat /docs/readme       # Read documentation
Lair:/> tetris                 # Play Tetris (found via PATH)
Lair:/> tcc /samples/hello.c   # Compile and run a C program
Lair:/> perl /samples/hello.pl # Run a Perl script

📁 Directory Structure

On-Disk (Virtual Drive)

/
├── bin/          190 utility programs (edit, grep, sort, tcc, wget, nc, ...)
├── games/         29 games (snake, tetris, galaga, pacman, rogue, robotown, ...)
├── samples/       31 source files (hello.c, fib.c, hello.pl, fizzbuzz.pl, hello.bas, ...)
├── docs/           text files (readme.txt, license.txt, notes.txt, ...)
└── script.bat      Example batch script

Programs in /bin and /games are in the default PATH, so they run from any directory.

Source Tree

Mellivora_OS/
├── boot.asm               Stage 1 MBR boot sector (512 bytes, 16-bit)
├── stage2.asm              Stage 2 loader (A20, E820, long mode switch)
├── kernel.asm              Kernel entry + modular includes (22 files in `kernel/`)
├── Makefile                Build system (make full / make run / make debug)
├── populate.py             HBFS image populator with subdirectory support
├── CHANGELOG.md            Version history (v1.0 → v13.0.0)
├── README.md               This file
├── programs/               User-space assembly programs
│   ├── syscalls.inc        Shared syscall constants and helpers
│   ├── lib/                Reusable API libraries (string, io, math, vga, mem, data)
│   ├── hello.asm           Hello World
│   ├── edit.asm            Full-screen text editor
│   ├── snake.asm           Snake game
│   ├── tetris.asm          Tetris with rotation, scoring, levels
│   ├── galaga.asm          Space shooter
│   ├── tcc.asm             Tiny C Compiler (subset)
│   ├── grep.asm            Pattern search
│   ├── sort.asm            Line sorting
│   └── ...                 (231 programs total)
├── samples/                C, Perl, and BASIC source files
│   ├── hello.c, fib.c, primes.c, calc.c, matrix.c, hanoi.c
│   ├── bf.c, wumpus.c, boxes.c, stars.c, echo.c
│   ├── hello.pl, factorial.pl, fizzbuzz.pl, guess.pl, strings.pl, arrays.pl
│   ├── hello.bas, fib.bas, blackjack.bas, mandelbrot.bas, snake.bas
│   └── ...                 (31 samples total — 17 C + 9 Perl + 5 BASIC)
├── tests/                  Regression test suite
│   ├── test_build.sh       Build-time checks
│   └── test_hbfs.py        HBFS filesystem integrity checks
└── docs/                   Documentation
    ├── API_REFERENCE.md     Library API reference
    ├── INSTALL.md           Build & installation guide
    ├── USER_GUIDE.md        Shell commands & usage manual
    ├── PROGRAMMING_GUIDE.md Writing programs for Mellivora
    ├── TECHNICAL_REFERENCE.md  OS internals & architecture
    └── TUTORIAL.md          Step-by-step beginner tutorial

📖 Documentation

Document Description
Installation Guide Prerequisites, building, QEMU, real hardware
User Guide Complete shell command reference and usage
Programming Guide Writing assembly programs with syscalls
Technical Reference Architecture, memory map, HBFS, drivers
Tutorial Step-by-step beginner walkthrough
API Reference Library functions and calling conventions
Changelog Version history and release notes

🎮 Included Programs

Games

Program Description
snake Classic snake — eat food, grow, avoid walls and tail
tetris Tetris with 7 tetrominoes, rotation, scoring, levels
mine Minesweeper with flag and reveal mechanics
galaga Space shooter with enemy waves
blackjack Blackjack (21) card game
rogue ASCII dungeon crawler
adventure Text adventure (interactive fiction)
connect4 Connect Four
mastermind Mastermind code-breaking game
hangman Hangman word game
tictactoe Tic-tac-toe
simon Simon says memory game
guess Number guessing game with hints
kingdom Medieval kingdom management simulation
life Conway's Game of Life (78×23 grid)
maze Random maze generator with BFS solver
neurovault Sci-fi dungeon crawler RPG
outbreak Zombie survival strategy game
doomfire Doom fire effect demo
matrix Matrix rain effect
rain Rainfall animation
starfield Starfield fly-through
lunar Lunar lander game
solitaire Klondike solitaire card game
pacman Pac-Man-style 21×21 maze chase — eat dots and power pellets, hunt or flee 4 ghosts
iago Othello / Reversi — VBE board with greedy-AI opponent and persistent wins
raycaster Wolfenstein 3D-style raycaster — fixed-point 16.16 math, WASD movement
robotown Robot Town — logic-puzzle adventure inspired by Robot Odyssey
breakout Breakout/Arkanoid clone — 5×10 bricks, three lives, LEFT/RIGHT paddle

29 games total in /games — run any from anywhere thanks to PATH.

Utilities

Program Description
edit Full-screen text editor with save/load
burrow Dual-pane file manager TUI (Midnight Commander-style)
tcc Tiny C Compiler — compile C to ELF inside the OS
grep Pattern search in files
sort Sort lines alphabetically
hexdump Hex/ASCII file viewer
sed Stream editor (search and replace)
tr Character translator
csv CSV file viewer with formatted columns
wc Line, word, and byte counter
pager File pager (like more)
cal Calendar with current day highlighted
calc Interactive calculator (+, -, ×, ÷, %)
mandel Mandelbrot set renderer (fixed-point)
mandelbrot Full-color Mandelbrot at 640×480×32 bpp, rainbow escape-time palette
julia Interactive Julia set renderer — arrow keys move c, +/- zoom
more Paging text viewer — SPACE=next page, ENTER=line, Q=quit
top Real-time process monitor with memory bar, refreshes every second
tar HBTAR1.0 flat archive — create, extract, list (up to 64 files)
nm ELF32 symbol table reader — address, type, and name
awk Pattern/action processor — $n, NR, NF, print, gsub, /regex/, BEGIN/END
basic GW-BASIC-style interpreter with strings, loops, DATA/READ, and file mode
bf Brainfuck interpreter

API Libraries (programs/lib/ and programs/)

Library Functions Description
string.inc 30+ String manipulation, comparison, search, memory ops
io.inc 20+ Console I/O, file operations, argument parsing
math.inc 10+ Number parsing/formatting, arithmetic
vga.inc 15+ VGA text mode, cursor, color, UI drawing
mem.inc 10+ Heap allocation, pool/arena allocators
data.inc 10+ Stacks, queues, bitmaps, dynamic arrays
net.inc 10+ TCP/UDP sockets, DNS, ICMP ping
gui.inc 10+ Burrows desktop GUI wrappers
sprite.inc 4 VBE sprite drawing: alpha, opaque, color-key, scaled

🔧 Build Targets

Command Description
make full Complete build: boot + kernel + programs + filesystem
make run Launch in QEMU (i486-compatible x86, 128 MB RAM)
make debug Launch with QEMU monitor on stdio
make iso Create a bootable installer/live ISO with docs included
make check Run the regression suite and HBFS integrity checks
make clean Remove all build artifacts
make sizes Show component sizes

🖥️ System Requirements

Emulation (Recommended)

  • QEMU 6.0+ with qemu-system-i386 (or qemu-system-x86_64 in compatibility mode)
  • Any modern host OS (Linux, macOS, Windows with WSL)

Real Hardware

  • i486-or-newer x86 CPU with BIOS legacy boot support
  • 1 MB RAM minimum (128 MB recommended)
  • IDE/SATA disk or USB drive (BIOS legacy boot)
  • VGA-compatible display
  • PS/2 keyboard

📊 Stats

Metric Value
Kernel source Entry file + 26 modular include files
Syscalls 182 (via INT 0x80)
Shell commands 90+ built-ins, aliases, history (128 entries), tab completion
User programs 231 assembly apps
Bundled samples 31 (17 C + 9 Perl + 5 BAS) in /samples
API libraries 17 reusable .inc modules in programs/lib/
Disk image 2 GB raw HBFS image
HBFS root capacity 455 files; 224 files per subdirectory
Concurrent tasks 128 (preemptive scheduler, 4 priority levels)

📜 License

This project is licensed under the MIT License.

Copyright (c) 2026 Honey Badger Universe

🦡 Why "Mellivora"?

Mellivora capensis — the honey badger. Small, tough, and fearless. Just like this OS.

Component Naming

Component Name Full Name
Kernel Mellivora Mellivora OS kernel
Init System Ratel Hardware & subsystem initialization
Shell HB Lair Honey Badger Lair
Filesystem HBFS Honey Badger File System
Utilities HBU Honey Badger Utilities (GNU-like tools)

About

Mellivora OS is a from-scratch hobby OS that boots on real x86 hardware or in QEMU. It includes a custom HBFS filesystem, ring 3 user-mode execution, a DOS-inspired interactive shell with POSIX features, 82 syscalls, priority-based preemptive scheduling, signal support, an in-OS Tiny C Compiler

github.com/James-HoneyBadger/Mellivora_OS#readme

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assemblybare-metalbootloaderdesktop-environmentfilesystemguihobby-oskernelmultitaskingnasmnetworkingoperating-systemos-developmentosdevqemutcp-ip

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