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|---|---|---|
953f9c5c3c
Guru and SchCotie are gone. Shift is the only mark, and the crash screen draws it where the face used to be. Guru was an icon -- a pictogram with a face, denoting one state -- that lived on the crash screen and nowhere else. Its argument was identity: `:(` is recognisably Microsoft's, and a crash screen is the single screenshot most likely to leave the machine, so it is the worst place to be wearing somebody else's face. That part holds, and it is kept in the branding README because it is the argument against any second mark. What does not follow is that the answer is a *new* mark. Shift already signs the system, it is already what the machine drew on the splash it started with, and a reader who has seen it twice before the crash recognises it faster than a face they have never seen. SchCotie was a mascot, and never existed: the file said so itself under "what this does not cover". A brief for a character nobody is about to draw is not worth carrying. So `draw_guru()` and its SVG-space geometry leave panic.c, the two `guru.svg` files are deleted, and PSOGM calls gfx_draw_logo() -- the same include/logo.h mask the loader splash and the boot console composite. At its native 128 px: there is no resampler in the crash path, and the face was scalable in a place that only ever drew it at one size. The name stays. "Purple Screen of Guru Meditation" is the Amiga nod, which panic.c's own header already called out as a separate thing from the mark. **And taking the screenshot to check it caught a regression from the TTF console work.** `gfx_draw_char()` -- the pixel-positioned path, which only PSOGM uses -- still walked `font_data[c][row]` for `row < CHAR_HEIGHT`. font_data has exactly 16 rows per glyph; CHAR_HEIGHT is the *TrueType* cell height now, about 21. So every line of the crash report drew five rows of the next character's bitmap underneath itself, and it looked like each line had been printed twice. The grid path had been updated when the cell size stopped being a constant; this one had not, because nothing routine draws text in pixel coordinates. Both go through one draw_glyph_px() now, and the bitmap's own geometry is spelled BITMAP_W/BITMAP_H so it cannot be mistaken for a cell size again. Two stale claims corrected while in there, in panic.c's header and in graphics.md: PSOGM has not dimmed-and-floated over the old screen for a while -- it clears to full purple, and the file's own code comment says why -- and there is no longer "a face that is obviously a cartoon". The website's crash section shows the mark in flat white rather than its own violets, which is what the kernel actually draws: PSOGM composites a coverage mask in one colour, and those violets sit close enough to #4B1D9A to half-disappear against it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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A 64-bit operating system, written from the metal up.
SMP · copy-on-write filesystem · TCP/IP · PCI, USB and virtio drivers · TrueType text · Linux syscall ABI
SchOS began as xv6 and is now mostly something else. The scheduler, the memory manager and the trap path have been rewritten for x86-64 and for more than one processor; the filesystem has been replaced outright; the syscall table speaks Linux numbering so that real software — musl, toybox, mksh — runs unmodified.
It is a hobby system built by one person, and it is honest about that: what works below has been run, not inferred, and the gaps are listed as plainly as the features.
The pieces
| Layer | Name | What it is |
|---|---|---|
| System | SchOS | The distribution — kernel, userland, tooling |
| Kernel | SchIFT | Multi-core x86-64 kernel with a modular VFS |
| Filesystem | SchFS | Transactional, copy-on-write, the root filesystem |
| API | SchAPI | System programming interface — the stable surface |
| Compositor | SchCom | Display compositor (planned) |
| Window manager | SchWM | (planned) |
| Desktop | SchDE | (planned) |
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. SMP: one, two and four processors all boot, with CPU enumeration from the ACPI MADT rather than the 1994 MP table. Memory sized from the E820 map, so it runs in tens of megabytes rather than demanding hundreds.
Filesystem — SchFS is the root: a copy-on-write B-tree with a
uberblock ring, so a crash leaves either the old tree or the new one and there
is nothing to repair. Free space is derived from the tree rather than stored
beside it, which removes a whole class of disagreement. /proc/schfs shows the
generation counter advancing as writes commit.
Processes — fork, exec, wait, pipes, signals, sessions and process groups,
mmap (anonymous and file-backed), POSIX shared memory, Unix domain sockets,
poll.
Devices — PCI enumeration with a bus-agnostic device model at
/proc/devices. Drivers for e1000 networking, virtio-gpu and stdvga
displays, xHCI USB with HID, hub and mass-storage class drivers, IDE, PS/2,
serial. /dev/fb0 speaks the Linux fbdev interface.
Networking — ARP, IPv4, ICMP, UDP, TCP and DHCP, on lwIP behind a
driver-agnostic interface class. Verified end to end from the host, both
directions, rather than by inspection. Names resolve, so wget http://host/
works; httpd serves a directory back the other way.
Userland — musl, toybox, mksh and zsh, built from source. 268 applets:
ls, cat, ps, top, wc, cp, mount, awk, bc, diff and the rest
behave the way you expect, because they are the real programs. edit is
kilo — arrow keys, Ctrl-S, Ctrl-Q, nothing
to learn.
Text — a TrueType rasteriser (glyf outlines, composite glyphs, cmap
format 4) replacing the 8×16 cell grid. JetBrains Mono for the terminal, Roboto
for the desktop layer to come.
When it dies — PSOGM, the Purple Screen of Guru Meditation: stop code, fault address, call chain, and a QR code containing a text copy of the whole report.
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
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. See docs/guides/building.md for prerequisites per platform, and docs/history/moving-to-linux.md for moving a checkout between machines.
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.
Layout
kernel/ arch/ core/ dev/ drivers/ fs/ net/ proc/ sys/
fs/schfs/ the filesystem -- same source the host tools compile
include/ kernel and userland headers
boot/ uefi/ (PE loader) common/ (shared loader UI)
lib/ cmd/ first-party userland runtime and programs
ports/ third-party software built from source
tools/ windows/ (.ps1) posix/ (.sh) python/ (.py) and .c/.pl
docs/ architecture/ (what it is) plan/ (what's next)
guides/ (how to work on it) history/ (why it's like this)
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.
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 desktop. Schcom composites and routes input; the plan is now to put it on Wayland and delete the homegrown protocol. See docs/plan/wayland.md.
- No descriptor passing. No
sendmsg/recvmsg, so noSCM_RIGHTS— which is what the GUI work stops at. docs/plan/foundations.md. - No dynamic linking.
exechandles staticET_EXEConly. - No page cache, so writable
MAP_SHAREDof a file is refused rather than faked. - A USB disk cannot be booted from — the root device is compiled in rather than selectable.
- 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
Apache-2.0, 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, zsh, kilo, the fonts) keeps its own licence; NOTICE carries the attributions. All of it is permissive — there is no GPL in an image this builds, which is why the userland is toybox and not BusyBox and the editor is kilo and not nano. See docs/licensing.md.
Drivers may be adapted from BSD sources, which are compatible. Linux drivers are not: GPL-2.0-only and Apache-2.0 cannot be combined and redistributed. Reading Linux to understand hardware is fine; translating a driver is not. Best of all is the public specification — xHCI, virtio, AHCI, e1000 — which carries no licence on what you write from it.