Crius

Crius is an x86-64 operating system written in C and assembly, using the Limine boot protocol.

Status: early development. The kernel and a minimal userspace (Nexus) build and run under QEMU.

What's included

• Kernel (kernel/) — 64-bit higher-half kernel with GDT/IDT/APIC, PMM/VMM, scheduler, system calls, VFS, ramfs, ext2, framebuffer console, PS/2 and USB HID keyboards, serial and IDE block devices.
• Nexus (nexus/) — a small userspace with libc, init, shell, coreutils, editor and tests.

Quick start

make        # build the kernel, userspace and create crius.iso
make run    # boot the ISO in QEMU (creates disk.img automatically if missing)

Build

The following tools are required. Exact package names depend on your distribution:

• gcc, ld, nasm, make — build toolchain
• git, curl — for downloading Limine and the freestanding headers
• xorriso — for creating crius.iso
• qemu-system-x86_64 (or your distribution's x86-64 QEMU binary) — for make run
• dd, sfdisk (usually from util-linux), and mkfs.ext2 (usually from e2fsprogs) — make run also creates a disk.img test image

make kernel     # build kernel.elf only
make nexus      # build userspace nexus.elf only

The Makefile downloads Limine v12.3.3 binaries and the freestanding-c-hdrs headers automatically.

Platform setup

Fedora

sudo dnf install gcc make nasm binutils xorriso qemu-system-x86 curl git util-linux e2fsprogs

Debian / Ubuntu

sudo apt install gcc make nasm binutils xorriso qemu-system-x86 curl git util-linux e2fsprogs

Windows

The official Crius build environment is Linux-based. On Windows, the recommended approach is WSL2:

1. Install WSL2 with Debian or Ubuntu:

   wsl --install -d Debian

2. Inside WSL2, follow the Debian / Ubuntu instructions above.
3. For better performance and compatibility, keep the project inside the WSL2 filesystem (/home/<user>/...) instead of /mnt/c/....

Project layout

abi/        Kernel/userspace ABI definitions
docs/       Technical documentation (start with docs/index.md)
kernel/     Kernel source and headers
nexus/      Userspace programs and libc
tools/      Build helpers and linker scripts

Documentation

Detailed technical documentation is in docs/index.md, including the architecture, kernel subsystems, system calls, file systems, userspace, build process, and current limitations.

License

This project is distributed under a custom license. See the LICENSE file for details.