Sushi

Sushi is a Rust boot splash stack for Linux: an initramfs daemon that owns the display from early boot through disk unlock and pivot, optional UEFI pre-boot graphics, and a dracut module that replaces Plymouth.

Components

Crate / binary	Role
sushi	Shared library: display backends (DRM/fbdev), renderer, protocol, unlock helpers
sushid	Initramfs splash daemon (rdinit=/usr/bin/sushid)
sushictl	Diagnostics and manual control CLI
sushi-bootctl	Install SushiBoot on ESP, kernel-install layout, signing
sushiboot	UEFI bootloader — scans all ESPs, auto-detects OS entries, minimal menu
90sushi	Dracut module under initramfs/dracut/90sushi/

Log prefixes in serial/console output: SushiBoot, Sushi, SushiDisplay.

Prerequisites

Host builds

• Rust 1.75+ (rustup)
• rustup target add x86_64-unknown-uefi (for SushiBoot)

QEMU VM

• qemu-system-x86_64, OVMF (OVMF_CODE.fd, OVMF_VARS.fd)
• A host kernel image (/boot/vmlinuz-* or set KERNEL=)
• busybox (for the minimal test root disk)
• cpio, gzip, mkfs.ext4, e2fsprogs

On Fedora:

sudo dnf install qemu-system-x86 edk2-ovmf busybox e2fsprogs cpio gzip

Quick start (QEMU)

Build the ESP, initramfs, and root disk, then boot:

make vm-build    # or: ./scripts/vm/build-esp.sh
make vm-run      # or: ./scripts/vm/run-qemu.sh

build-esp.sh produces:

• vm/esp/ — FAT ESP with BOOTX64.EFI, kernel, initramfs, BLS entry
• vm/rootfs.img — ext4 busybox root on whole /dev/vda
• vm/initramfs-sushi.img — minimal initramfs with sushid

Useful environment variables:

Variable	Default	Purpose
KERNEL	latest /boot/vmlinuz-*	Kernel copied to the ESP
USE_DRACUT	0	1 builds initramfs via dracut (needs staging install + sudo)
HEADLESS	0	1 runs QEMU with -display none, serial on stdout
DISPLAY_BACKEND	gtk	QEMU display backend when not headless

Serial log when using the GTK window: vm/serial.log.

Production install

make build
sudo make install DESTDIR=/   # sushid, sushictl, sushi-bootctl, dracut, kernel-install
sudo sushi-bootctl install --sign --efi-entry
sudo dracut --force --omit plymouth --add sushi
sudo kernel-install add "$(uname -r)"   # or: dracut --regenerate-all

Secure Boot (optional): sudo sbctl create-keys && sudo sbctl enroll -m, then sudo sushi-bootctl sign. Dual-boot Windows: sudo sushi-bootctl add-windows.

Kernel cmdline (enabled by default when the module is installed):

rd.sushi=1

Rebuild initramfs after upgrading sushid or the dracut module.

Development

cargo test --workspace --exclude sushiboot
cargo build --workspace --exclude sushiboot

SushiBoot links as a UEFI application; build scripts set the required RUSTFLAGS (no checked-in .cargo/ config).

RUSTFLAGS='-C link-arg=-Wl,--subsystem,efi_application' \
  cargo build -p sushiboot --target x86_64-unknown-uefi --release

Boot flow (VM)

SushiBoot (UEFI) → kernel + initramfs → sushid (splash + unlock) → switch_root → busybox on tty

The BLS entry uses root=/dev/vda (whole virtio disk), rdinit=/usr/bin/sushid, and both console=ttyS0 and console=tty0 for debugging.

Troubleshooting

Black screen after boot

• Confirm serial shows Sushi: caught the frame — if not, initramfs may not be loading (initrd=\initramfs.img path on the ESP).
• Check vm/serial.log for Sushi: / SushiDisplay: lines.
• Rootfs sbin/init must use relative busybox symlinks (../bin/busybox).

SushiBoot build fails

rustup target add x86_64-unknown-uefi

License

MIT