256-byte-vm

A bootable x86 VM whose program is a single 256-byte file (boot.bin). The build step wraps it into raw, qcow2, vdi, vmdk, vhd and iso images that boot on QEMU, Proxmox, VMware, VirtualBox, Hyper-V, and any BIOS PC.

Banner ClientAPI prints to BIOS video and COM1 serial. A serial REPL echoes each typed line back reversed (hello → olleh). The guest reacts to the hypervisor's ACPI power-button event — i.e. qm shutdown on Proxmox — by writing SLP_EN to PM1a_CNT so the VM exits cleanly to S5 instead of being force-killed after the shutdown timeout.

Output formats

make all produces every common VM disk format from boot.bin:

File	Format	Use case
boot.bin	raw program	dd / hexdump / xxd
boot.iso	ISO 9660 + El Torito	bootable CD / qemu -cdrom
boot.qcow2	QCOW2	Proxmox, libvirt, KVM
boot.vmdk + boot-flat.vmdk	VMware monolithicFlat	VMware Workstation / ESXi
boot.vhd	Microsoft VHD	Hyper-V, Azure
boot.vdi	VirtualBox VDI	VirtualBox
boot.img	raw bootable disk	qemu -drive format=raw

Build

sudo apt-get install -y nasm qemu-utils xorriso
make all

Outputs land in build/.

Run locally

make run          # boot raw disk in qemu, screen + serial multiplexed
make run-serial   # boot raw disk, serial-only
make run-iso      # boot ISO in qemu
make test         # banner + REPL + ACPI shutdown e2e

Quit qemu with Ctrl-A X.

Use on Proxmox

As a CD image

# Upload boot.iso to your ISO storage (e.g. local:iso) and attach.
qm create 9999 --memory 64 --net0 virtio,bridge=vmbr0 \
  --ide2 local:iso/boot.iso,media=cdrom \
  --boot order=ide2
qm start 9999
qm terminal 9999    # serial console

As a disk image

qm importdisk 9999 build/boot.qcow2 local-lvm
qm set 9999 --scsi0 local-lvm:vm-9999-disk-0
qm set 9999 --boot order=scsi0
qm start 9999
qm terminal 9999
qm shutdown 9999    # ACPI power-button — guest reacts via SLP_EN

Inspect

make check        # validate boot.bin size + code+data fits
make size         # one-line size report

$ make size
222 / 256 bytes (34 free)

What fits in 256 bytes

• COM1 init at 9600 8N1
• BIOS teletype output (int 0x10 AH=0Eh)
• Serial RX poll, line buffer (80 chars), in-place reverse, echo back
• ACPI PM1a_EN write to arm the power-button event source
• ACPI PM1a_STS polling for the hypervisor shutdown request
• ACPI S5 shutdown via SLP_EN write to PM1a_CNT

License

Apache 2.0 — see LICENSE.