Cervus is a 64-bit operating system written from scratch for the x86_64 architecture. Everything — kernel, C library, userland, installer, shell, text editor — lives in this repository. There is no Linux compatibility layer, no busybox, no external libc.

The goal is a self-hosting, minimal but actually usable Unix-style environment: boot from BIOS or UEFI, install onto a real disk, log in, edit and compile C code on the machine itself.

Boot and core kernel

• BIOS and UEFI boot via Limine.
• Physical memory manager (bitmap), virtual memory manager with 4-level paging.
• Custom GDT and IDT, full interrupt and exception handling.
• ACPI table parsing, APIC / IOAPIC / LAPIC, HPET and APIC timer.
• SMP (multicore) initialization with per-CPU structures.
• SSE/AVX support with proper FPU state save and restore.
• Preemptive scheduler with fork / exec / wait / waitpid, pipes, and basic signals.
• ~60 kernel syscalls accessible from userspace.

Buses and devices

• PCI / PCIe enumeration via ACPI MCFG with legacy 0xCF8/0xCFC fallback. Recursive bridge walk, BAR sizing (incl. 64-bit), capability-list parsing, MSI and MSI-X enable. Driver matching framework keyed on vendor/device or class/subclass.

Filesystems and storage

• Virtual filesystem layer with mount points.
• ext2 read/write, including in-kernel mkfs.ext2.
• FAT32 read/write, including in-kernel mkfs.fat32.
• initramfs for the Live ISO, ramfs, devfs (/dev/tty, /dev/null, /dev/zero).
• ATA disk driver, generic block-device layer, MBR partition table parsing.

Userland

• Own C library libcervus — POSIX-style API, ~230 source files, split one function per .c. Private internals isolated in a single <libcervus.h> header.
• 45+ utilities under /bin: cat, ls, cp, mv, rm, mkdir, find, grep, head, tail, wc, sort, uniq, diff, tee, sleep, touch, stat, ps, kill, env, echo, basename, dirname, pwd, true, false, which, whoami, uname, hexdump, seq, yes, clear, reboot, shutdown, mkfs, mount, umount, lsblk, lspci, diskinfo, meminfo, cpuinfo.
• Apps under /apps: interactive login shell, neo text editor (modal-free, nano-style), calculator, calendar, date, system fetch, uptime, and a set of process / IO / memory test programs.
• Two shells: the interactive login shell, and csh for scripting, with if/else/endif, foreach, while, redirects, pipes, environment variables and $status.
• Bundled TCC — the system can compile C code on itself, without a host toolchain.

Live ISO and installer

• Cervus boots from ISO as a Live system using initramfs.
• The bundled install-on-disk wipes a chosen disk, writes an MBR, formats ESP (FAT32, 64 MB) + root (ext2) + swap (16 MB), copies the system tree, writes limine.conf to three locations and installs Limine BIOS stage1.
• After install the system boots directly from the disk image with no ISO required.

• No black boxes. Every layer from _start to cat lives in this repository. ~13k lines of kernel C, plus a clearly factored libc and userland. The whole stack can be read end-to-end.
• Not a Linux clone. Cervus has its own kernel ABI, its own syscall numbers, its own libc. It speaks POSIX where reasonable, but is not bound to Linux internals — no /proc assumption, no clone flags, no glibc ABI.
• Real userland. Not a "kernel that prints hello". There is an actual shell with history, a usable text editor, a working compiler, a real filesystem on a real disk, an installer that produces a bootable system.
• One-command build. ./build run produces an ISO and launches QEMU. The build system is a single C binary, checked into the repository.

kernel/             x86_64 kernel
  src/
    drivers/        ata, ps/2, timer, block device, partitions, pci
    fs/             vfs, ext2, fat32, initramfs, ramfs, devfs
    memory/         pmm, vmm, paging
    sched/          scheduler, task state, fork/exec
    syscall/        syscall table and dispatch
    apic/           LAPIC, IOAPIC
    acpi/           ACPI table parsing
    smp/            multicore startup
    graphics/       framebuffer + PSF font rendering
    sse/            FPU/SSE state handling

usr/
  lib/libcervus/    C library, one function per .c, private <libcervus.h>
    unistd/  fcntl/  sys/{stat,mman,wait,utsname}/
    string/  stdio/{printf,scanf}/  stdlib/  ctype/  time/
    termios/  signal/  dirent/  math/  cervus/  internal/
  apps/             interactive shell, neo editor, calc, test programs
  bin/              coreutils-style userland (45+ programs)
  installer/        disk installer (Live ISO only)
  sysroot/          public headers
  tcc/              ported Tiny C Compiler

builder/            single-binary build system written in C
limine.conf         boot config

Cervus builds with a regular host Linux toolchain — no cross-compiler required.

• Compiler: gcc
• Assembler: nasm
• Archiver: ar (binutils)
• Emulation: qemu-system-x86_64
• ISO tools: xorriso, mtools

1. Clone the repository:

git clone https://github.com/VeoQeo/Cervus.git
cd Cervus

2. Build everything and launch in QEMU:

./build 

A full list of build commands is available via ./build help.

Cervus is an open-source research project. Contributions to drivers, additional utilities, bug fixes, hardware support and documentation are welcome. Open an Issue or send a Pull Request.

This project is licensed under the GPL-3.0 License. See the LICENSE file for details.