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EXOS Screenshot-01

Status

Platform Platform Build Boot Boot

Other languages

🇪🇸 Español | 🇫🇷 Français | 🇯🇵 日本語

TL;DR

Multi-threaded operating system for IA32 (i386-i686) and x86-64 (core 3-9, etc...).
Runs on QEMU, Bochs, and real hardware.
NOT READY for production (disk I/O incomplete).

Disclaimer

EXOS is provided "as is", without warranty of any kind. Neither EXOS authors/contributors, nor the authors/contributors of bundled third-party software, can be held liable for any direct, indirect, incidental, special, exemplary, or consequential damages arising from the use of this project.

License

The EXOS codebase is licensed under GPLv3, except for the runtime under runtime/, which is licensed under MIT. See LICENSE and runtime/LICENSE.
Third-party products stored under third/ are subject to their own licenses; refer to each component's license file in third/.

Quick note on license "contamination" (copyleft propagation):

  • MIT code can be included in GPLv3 projects.
  • If distributed as one combined work with GPLv3 code, the resulting distribution must comply with GPLv3 terms.
  • Third-party components in third/ keep their own license obligations (notice, attribution, and compatibility requirements).

Debian compile & run

Using the provided dashboard

./dashboard.sh

Or manually via scripts

Setup dependencies

./scripts/linux/setup/setup-deps.sh

./scripts/linux/setup/setup-qemu.sh <- if you want a recent QEMU (9.0.2)

Build (Disk image with ext2)

./scripts/linux/build/build --arch <x86-32|x86-64> --fs ext2 --release (or --debug)

( add --clean for a clean build )

Build (Disk image with FAT32)

./scripts/linux/build/build --arch <x86-32|x86-64> --fs fat32 --release (or --debug)

( add --clean for a clean build )

Build for UEFI boot

./scripts/linux/build/build --arch <x86-32|x86-64> --fs ext2 --release (or --debug) --uefi

( add --clean for a clean build )

Run

./scripts/linux/run/run --arch <x86-32|x86-64>

( add --gdb to debug with gdb ) ( or ./scripts/linux/x86-32/start-bochs.sh to use Bochs on x86-32 )

Things it does

  • Multi-architecture : x86-32, x86-64
  • Multi-threaded : software context switching
  • Virtual memory management (CPU & DMA mapping) (buddy allocator for physical pages)
  • Heap management (free lists)
  • Process spawning (kernel and userland), task spawning, scheduling
  • Binary executable and library loading, thread local storage
  • Security at kernel object level, with user account/session and permissions
  • Kernel pointer masking : handles in userland
  • File system drivers : FAT16, FAT32, EXT2, NTFS ~
  • I/O APIC & Local APIC drivers
  • PCI device driver
  • ATA, SATA/AHCI & NVMe storage drivers
  • xHCI driver (USB 3)
  • GOP (UEFI framebuffer) driver
  • VGA/VESA/iGPU drivers
  • PS/2 keyboard and mouse drivers
  • USB keyboard (HID) and mouse drivers
  • USB mass storage device driver ~
  • Console management
  • Virtual file system with mount points
  • Shell with embedded scripting and kernel objects exposure
  • Configuration with TOML format
  • E1000 / Realtek RTL8139 & RTL8111/8168/8411 network drivers ~
  • ARP/IPv4/DHCP/UDP/TCP network layers ~
  • Minimal HTTP client ~
  • Desktop/windowing system (WIP)
  • Native C compiler (TinyCC integration)
  • ACPI shutdown/reboot
  • A few test apps

(~ means working in emulator - QEMU, but not tested or not yet working on bare metal)

Things it will do

  • IPC (shared memory through page mapping)
  • Multi-core (SMP)
  • Full security
  • Full network stack
  • Full Unicode
  • PCIe driver
  • VMD (Volume Management Device - Intel)
  • HDA audio (Intel HD Audio)
  • NVIDIA GeForce driver
  • AMD Radeon driver
  • Larger test apps
  • ACPI Energy sensor drivers

Beyond

  • More architectures (ARM64, RISC-V)
  • More drivers

Architecture

See doc/guides/Kernel.md for architecture details

Dependencies

C language (no headers)

bcrypt

Used for password hashing. Sources in third/bcrypt (under Apache 2.0, see third/bcrypt/README and third/bcrypt/LICENSE).
Compiled files in kernel: bcrypt.c, blowfish.c.
bcrypt is copyright (c) 2002 Johnny Shelley jshelley@cahaus.com

BearSSL

Used for SHA-256 hashing in kernel crypt utilities. Sources in third/bearssl (MIT license, see third/bearssl/LICENSE.txt and third/bearssl/README.txt).
Integrated SHA-256 sources: third/bearssl/src/hash/sha2small.c, third/bearssl/src/codec/dec32be.c, third/bearssl/src/codec/enc32be.c.
BearSSL is copyright (c) 2016 Thomas Pornin pornin@bolet.org.

miniz

Used for DEFLATE/zlib compression in kernel compression utilities. Sources in third/miniz (MIT license, see third/miniz/LICENSE and third/miniz/readme.md).
Integrated kernel backend source: third/miniz/miniz.c.
miniz is copyright (c) Rich Geldreich, RAD Game Tools, and Valve Software.

Monocypher

Used for detached signature verification (Ed25519) in kernel signature utilities. Sources in third/monocypher (BSD-2-Clause OR CC0-1.0, see third/monocypher/LICENCE.md and third/monocypher/README.md).
Integrated signature backend sources: third/monocypher/src/monocypher.c and third/monocypher/src/optional/monocypher-ed25519.c.
For kernel freestanding compatibility, Monocypher Argon2 is disabled in x86-32 builds.
Monocypher is copyright (c) 2017-2019 Loup Vaillant.

utf8-hoehrmann

Used for UTF-8 decoding in layout parsing. Sources in third/utf8-hoehrmann (MIT license, see headers).

Fonts

Bm437_IBM_VGA_8x16.otb from the Ultimate Oldschool PC Font Pack by VileR, licensed under CC BY-SA 4.0. See third/fonts/oldschool_pc_font_pack/ATTRIBUTION.txt and third/fonts/oldschool_pc_font_pack/LICENSE.TXT.

Metrics (cloc)

Lines of code in this project, excluding third party software.

-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                              375          35649          36727         121576
C/C++ Header                   274           6576           7051          16699
Assembly                        22           1994           1249           6952
-------------------------------------------------------------------------------
SUM:                           671          44219          45027         145227
-------------------------------------------------------------------------------

Kernel size

- 32 bit : 1.4 mb
- 64 bit : 1.8 mb

Historical background

In 1999, I started EXOS as a simple experiment: I wanted to write a minimal OS bootloader for fun.
Very quickly, I realized I was building much more than a bootloader. I began to re-implement full system headers, taking inspiration from Windows and low-level DOS/BIOS references, and a bit of Linux (which I barely knew about at that time), aiming to create a complete 32-bit OS from scratch.

It was a year-long solo project, developed the hard way:

  • On a Pentium, in DOS environment, without any debugger or VM
  • Relying on endless console print statements to trace bugs
  • Learning everything on the fly as the project grew

Back then, it was 32 bit only and compiled with gcc and nasm, and linked with jloc.
In summer 2025, I ported the project to i686-elf-gcc/nasm/i686-elf-ld, then ported to x86-64.

EXOS’ coding style resembles that of Windows, like PascalCase naming, user function names, etc... Some will like it, others won't. But it is not Windows. It is more compact and will never collect or transmit user data. Ever. (Except possibly crash dumps for debugging.)