usbwin

This is the tool Rufus refuses to be.

A native macOS arm64 CLI for writing bootable USB sticks from any ISO — Windows (7 through 11), Linux/BSD (hybrid or isolinux), or UEFI-only — without Rosetta, without a Windows VM, without Boot Camp Assistant.

Status

Alpha. Two modes work; one is in active debugging; the rest are deferred.

Mode	State
Hybrid (Linux/BSD ISO raw write)	✅ working since v0.1
Windows 7+ (BOOTMGR chain)	✅ hardware-verified on Dell E6410 (2026-05-19) with both --boot-record=bootrec (default) and --boot-record=ms-sys. Same code path covers Win 8/10/11.
Windows XP	⚠️ boot chain wired through text-mode setup as of 2026-05-19; stack of known kludges documented in docs/TECH_DEBT.md, not yet recommended for daily use.
Linux/isolinux	deferred
UEFI-only	deferred

The MBR + FAT32 PBR bytes come from the sibling mkmsbr library (renamed from bootrec 2026-05-19) by default, linked in-process — no external ms-sys binary required. The legacy ms-sys shell-out is still available as --boot-record=ms-sys for byte-equality auditing of Win 7 mode. usbwin imports it as bootrec::* via a Cargo package = "mkmsbr" alias for source-compat.

See docs/ARCHITECTURE.md for the design, docs/V0.3_WINDOWS_XP.md for the XP recipe (and how it deviates from "clean"), and docs/TECH_DEBT.md for what we know is wrong but haven't fixed yet.

Why

• UNetbootin requires Rosetta.
• Rufus is Windows-only.
• Boot Camp Assistant was removed on Apple Silicon.
• dd works for hybrid ISOs but silently produces a non-bootable Windows USB.

There is currently no native macOS arm64 binary that writes a bootable Windows install USB. This is that binary.

Install

# Build from source (requires Rust stable + NASM for mkmsbr's NASM blobs)
brew install nasm
git clone https://github.com/jma24/mkmsbr ../mkmsbr   # path dep — see Cargo.toml
git clone https://github.com/jma24/usbwin
cd usbwin
cargo build --release
sudo cp target/release/usbwin /usr/local/bin/

The embed-boot-asm feature on bootrec is enabled by usbwin's Cargo.toml, so a plain cargo build --release is enough — no extra flags.

Optional: ms-sys fallback

By default, usbwin uses the in-process bootrec library for MBR and FAT32 PBR bytes. If you want byte-for-byte equivalence with the upstream tool (useful for auditing or comparison against a known-good Win 7 USB), pass --boot-record=ms-sys and install ms-sys once:

git clone https://gitlab.com/cmaiolino/ms-sys.git /tmp/ms-sys
cd /tmp/ms-sys && make
sudo cp bin/ms-sys /usr/local/bin/
# Or without sudo: export USBWIN_MS_SYS=/tmp/ms-sys/bin/ms-sys

Hybrid mode (Linux/BSD ISOs) does not touch the boot-record path at all.

Notarized signed binaries via GitHub Releases: TODO.

Test prerequisites

The default cargo test only needs Rust. Boot-record-level integration tests (QEMU smoke, ms-sys byte-equality) live in the bootrec repo — run them there.

Usage

usbwin <iso-path> <device>
       [--type=auto|windows|windows-xp|linux|hybrid|uefi]
       [--label=<volume-label>]
       [--boot-record=bootrec|ms-sys]
       [--dry-run]
       [--force]
       [--verbose]
       [--no-verify]

Examples:

sudo usbwin Win7_SP1.iso /dev/disk8
sudo usbwin ubuntu-22.04.iso /dev/disk8 --type=hybrid
sudo usbwin winxp_sp3.iso /dev/rdisk6 --type=windows-xp     # XP auto-detect is unreliable
usbwin --dry-run Win7_SP1.iso /dev/disk8     # no sudo needed; emits bytes to /tmp

Windows XP installs require --type=windows-xp explicitly — the auto-detector currently misclassifies XP ISOs.

Safety

usbwin will refuse to write to:

• The boot disk
• Any disk flagged internal: true by DiskArbitration
• Disks larger than 256 GiB without --force

Every write is verified by re-reading and byte-comparing unless --no-verify is passed.

License

MIT. See LICENSE.

Boot record source code lives in the separate bootrec repo, with its own clean-room provenance trail.