SchOS

A 64-bit operating system, written from the metal up — and it runs Linux's software.

SMP kernel · copy-on-write filesystem · Linux syscall ABI · Alpine packages · Xorg · Linux's own drivers

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SchOS is a hobby operating system built by one person. It began as xv6 and almost nothing of that is left: the scheduler, the memory manager, the trap path and every driver have been rewritten for x86-64 and for more than one processor, and the filesystem is a different one. The syscall table speaks Linux's numbering, so real Linux programs run on it unmodified — statically or dynamically linked, straight out of Alpine's package repositories — and a desktop (Xorg and Window Maker) and a web browser (NetSurf) come up on the framebuffer.

It is honest about being a hobby system: what is listed below has been run, not inferred, and the gaps are listed as plainly as the features. It boots from a USB stick on three different real machines.

In numbers

First-party code	72,766 lines, plus 23,670 lines of comments (25%) in 307 files
Kernel (kernel/, include/)	51,893 lines of code, 17,213 of comments
Syscalls	215, of which 193 on Linux numbering
Drivers	15 in the kernel
First-party programs	29 in cmd/
Alpine packages in the root	179, from 29 asked for in ports/alpine/world
History	292 commits since 2026-08-09 (78 days)

Lines by language

Language	Code	Comments
C	67,615	21,904
Assembly	1,750	336
PowerShell	1,362	638
Python	943	150
Shell	896	531
Perl	129	45
Linker script	71	66

_{Measured by tools/python/stats.py; first-party code only, so ports/ and generated tables are not counted.}

What it is made of

Layer	Name	What it is
System	SchOS	The distribution — kernel, userland, tooling
Kernel	SchIFT	Multi-core x86-64 kernel with a modular VFS and Linux's syscall ABI
Filesystem	SchFS	Transactional, copy-on-write, the root filesystem
Image format	SCFF	The SchOS Compressed File Format the live root ships in
Packages	apk	Alpine's package manager manages the root; SchOS itself is the package schos-base
Desktop	Xorg + Window Maker	Alpine's, on the framebuffer
Crash screen	PSOGM / GMMOS	The Purple Screen of Guru Meditation, and the micro OS that runs under it
API	SchAPI	The long-term native interface — designed, not built

uname -s reports SchIFT, the way every Unix reports its kernel rather than its distribution.

What works

Kernel — Long mode, 4-level paging, preemptive multitasking, a fair-share scheduler with nice. SMP up to 64 processors, enumerated from the ACPI MADT. Threads (clone, futex, TLB shootdowns), demand paging for the huge reservations browsers make, and dynamic linking. ACPI through uACPI: interrupt routing, the power button, clean power-off and reset, batteries and AC through a laptop's embedded controller, and deep idle states. Memory sized from the firmware's map, up to 256 GB.

Filesystem — SchFS is the root: a copy-on-write B-tree with an uberblock ring, so a crash leaves either the old tree or the new one and there is nothing to repair. The live image ships as SCFF: the root compresses with zstd to about a third of its size and is unpacked a chunk at a time, the first time something reads it. /proc, /sys and /dev are synthesised, in Linux's layouts, because that is what the programs read.

Linux software — fork, clone, exec, pipes, signals, sessions and job control, mmap, POSIX and memfd shared memory, Unix sockets with descriptor and credential passing, poll, epoll, eventfd, timerfd, signalfd, inotify, pseudo-terminals. The root is managed by Alpine's apk: ports/alpine/world says what is installed, world.lock pins it, and apk add fetches more over HTTPS.

Desktop — Xorg with Window Maker, xterm, the classic X clients, SDL games and the NetSurf browser, on the framebuffer (/dev/fb0, Linux fbdev) with input as Linux evdev. Twelve virtual terminals, switched with Ctrl+Alt+F1–F12, with X on a terminal of its own. Sound through ALSA (over OSS and an AC'97 driver).

Drivers — written from the specifications, and Linux's own, unmodified, through LDLS: a .ko runs in an ordinary process and reaches the hardware through /dev/pci, so a crashed driver costs an interface, not the machine. The laptop's Realtek NIC is driven that way.

Storage	AHCI (SATA), NVMe, IDE, USB mass storage
Network	Intel e1000, Realtek RTL8139 and r8169 (the latter also as Linux's driver in a process)
USB	xHCI, hubs, HID keyboards and mice
Input	PS/2, I2C-HID laptop touchpads and keyboards (DesignWare I2C, found through ACPI)
Display	UEFI GOP framebuffer, virtio-gpu, Bochs/stdvga
Audio	AC'97

Networking — ARP, IPv4, ICMP, UDP, TCP and DHCP on lwIP; DNS, wget and curl over HTTPS, ping, httpd, netlink for getifaddrs.

When it dies — PSOGM, the Purple Screen of Guru Meditation: stop code, fault address, call chain, and the log as QR codes. Under it runs GMMOS, a micro OS with its own keyboard drivers, so a dead machine can still show its log, take a few commands, and restart or power off.

On real hardware — booted from a USB stick on an AMD B550 desktop (Ryzen 5 4600G), an ASUS TUF A15 laptop and an Ivy Bridge HP all-in-one.

Quick start

make          # kernel + UEFI loader + root filesystem
make qemu     # build it and boot it
make iso      # a bootable ISO for VMware or real hardware
./write.sh sdX   # write that ISO to a USB stick (Linux; it checks what it is overwriting)

The ISO is a hybrid image: it boots on any UEFI machine from a stick written with write.sh, dd if=schos.iso of=/dev/sdX bs=4M, or Rufus/Etcher in DD mode. It runs from RAM and touches none of the machine's disks. Log in on the console, and type startx for the desktop.

Builds on Linux, macOS, FreeBSD/OpenBSD/NetBSD and Windows (Git Bash). The toolchain is clang + lld everywhere — it is a cross-compiler by construction, so one LLVM install targets the bare-metal kernel, the 16-bit boot code and musl userland from any host; nix-shell supplies all of it. See docs/guides/building.md for prerequisites per platform.

Testing

Booting to a prompt proves nothing: a filesystem can mount and still fail the first real command, and that has happened here. So the test harness drives the serial console and asserts on what comes back.

tools/windows/bootcheck.ps1            # boot, run real commands, check the answers
tools/windows/bootcheck.ps1 -Tty -Ps   # terminal behaviour, process enumeration
make schfs-check                       # SchFS B-tree, object and image suites

bootcheck is PowerShell because pwsh runs on every supported host. Several programs in cmd/ (socktest, memfdtest, xready, …) exist to be run on the system and report which of their own checks failed. See docs/guides/testing.md for what each proves. The numbers at the top are measured, not typed: python3 tools/python/stats.py rewrites them here and on the website.

Layout

kernel/     arch/ core/ dev/ drivers/ fs/ net/ proc/ sys/ acpi/ gmmos/ scff/
  fs/schfs/     the filesystem -- same source the host tools compile
ldls/       the Linux driver layer: the .ko loader, BTF reader, Linux symbols
include/    kernel and userland headers, by subsystem (arch/ core/ fs/ dev/ ...)
boot/       uefi/ (PE loader)  common/ (shared loader UI)
lib/ cmd/   first-party userland runtime and programs
etc/        what the image starts with: schinit's job manifests, motd, ...
ports/      third-party software built from source; ports/alpine is the apk root
tools/      windows/ (.ps1)  posix/ (.sh)  python/ (.py)  and .c/.pl
projects/   things that run ON SchOS (an installer, SchFS for Linux: both frozen)
docs/       architecture/ (what it is)  plan/ (what's next)
            guides/ (how to work on it)  history/ (why it's like this)
            Website/ (the site, and the docs reader)

docs/README.md is the index. If you are reading the tree for the first time, docs/architecture/README.md is the system layer by layer, and docs/plan/1.0.md says where it stands against its finish line.

One rule worth knowing: the kernel and the host tools compile the same SchFS source. mkschfs cannot disagree with the kernel about the on-disk format, because there is only one implementation — found and fixed on the host, where a test takes a second instead of a boot.

Another: syscalls are declared in exactly one place, kernel/sys/table.inc. Everything else is generated from it.

Not there yet

• No installer, and nothing persists. The live image runs from RAM and writes nothing to the machine's disks, so what you install or save is gone at reboot. This is the one thing between the system and its 1.0 definition.
• No GPU acceleration. Xorg draws in software; the plan is Linux's amdgpu through LDLS (docs/plan/gpu.md). There is no IOMMU either, so a driver in a process is isolated against its bugs, not against malice.
• udev sees the kernel's own devices only. eudev runs and Xorg finds its input devices through it; PCI and USB devices are not yet in the /sys/devices tree.
• WebKit browsers do not start. NetSurf does; Epiphany's web process dies at start-up, and it has not been run to ground.
• USB 2.0 controllers (EHCI) have no driver. On older machines the ports wired only to EHCI do nothing; xHCI ports work.
• Touchpads run in mouse mode: pointer, click and tap, but no two-finger scroll yet.
• No page cache, so writable MAP_SHARED of a file is refused rather than faked, and mprotect is accepted and ignored (nothing has NX).
• No Wi-Fi, no HDA audio, and the Realtek NIC on the laptop has reached the point of finding its PHY; whether it carries traffic there is not confirmed.
• SchFS has no Linux driver yet; the plan is on-disk format version first, then FUSE, then a kernel module.
• CFF/OpenType outlines and TrueType hinting are deliberately out of scope.

Licensing

GPL-2.0-or-later, copyright Nexoniarz. See LICENSE.

The kernel derives from xv6, which is MIT — see LICENSE.MIT. Third-party code redistributed in a built image (musl, toybox, mksh, zstd, the fonts, and Alpine's packages, each under its own licence) keeps that licence; NOTICE carries the attributions. See docs/licensing.md.

Drivers may be adapted from BSD sources and, since the move to the GPL, from Linux — GPL-2.0-only code combines with GPL-2.0-or-later, and the result ships under GPLv2. Linux's own drivers run unmodified through LDLS, and the ISO ships the Realtek r8169 set and its firmware; their licences and source are in NOTICE. Best of all is still the public specification — xHCI, virtio, AHCI, e1000 — which carries no licence on what you write from it.

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_{Built with stubbornness and a serial console.}