x0ne OS / Handbook / Run x0ne OS

Run as a microVM

Works today, built from source (measured 2026-10-12). Boots to the login prompt under QEMU microvm, Firecracker and Cloud Hypervisor. Not published yet. Boot time is measured below.

x0ne OS as a microVM: its own kernel, hardware isolation, no firmware and no PCI. Target: login in under 1.5 s, measured by make bench-boot.

Measured 2026-10-09 with make bench-boot, KVM on an AMD Ryzen 9 7900X, warm page cache, 20 boots each: login prompt at 0.85 s median (p95 0.92 s) under QEMU -M microvm, 0.64 s (p95 0.71 s) under Firecracker. The UEFI qcow2 takes 5.9 s.

Two kinds

• Interactive: a shell in a fresh VM, for an agent, a lab or a test.
• Service: one service per microVM, in the style of smolBSD. It boots, serves, and holds nothing else.

A microVM runs CPU inference only. Neither Firecracker nor QEMU microvm passes a GPU through. See GPUs.

Prerequisites

• Linux with KVM (/dev/kvm writable by you).
• QEMU 10 or Firecracker.
• The image files. Today: built from source, see Building x0ne OS from source.

What the image contains

QEMU microvm

This is the boot test command, with the serial console on your terminal. The disk is never written.

$ qemu-system-x86_64 -M microvm,accel=kvm,rtc=off -cpu host -m 512 -smp 2 \
    -nodefaults -no-user-config -display none -no-reboot \
    -kernel vmlinuz-microvm -initrd initrd-microvm.img \
    -append "console=ttyS0 root=/dev/vda rw quiet" \
    -drive id=root,file=x0ne-os-microvm-amd64.qcow2,format=qcow2,if=none,snapshot=on \
    -device virtio-blk-device,drive=root -serial stdio

Firecracker

Firecracker takes a raw disk and the ELF kernel.

$ qemu-img convert -O raw x0ne-os-microvm-amd64.qcow2 root.raw
$ firecracker --no-api --config-file fc.json

{"boot-source":{"kernel_image_path":"vmlinux-microvm","initrd_path":"initrd-microvm.img",
  "boot_args":"console=ttyS0 root=/dev/vda rw quiet reboot=k panic=1"},
 "drives":[{"drive_id":"root","path_on_host":"root.raw","is_root_device":false,"is_read_only":false}],
 "machine-config":{"vcpu_count":2,"mem_size_mib":512}}

Expected output

x0ne-boot-report: listening tcp=0 udp=0

Debian GNU/Linux 13 x0ne ttyS0

x0ne login:

On the first boot, x0ne OS asks for your account before this prompt, or takes it from credentials. See First boot and your account.

The launcher

scripts/x0ne-vm starts the microVM from the build output, in the VMM container. make run-microvm does the same with the defaults. works today

$ scripts/x0ne-vm -m 512 -c 2 -p 8080:80
# -m MiB of memory, -c vCPUs, -p HOST:GUEST TCP forward (turns the network on)
# -k qemu|firecracker|cloud-hypervisor, -s snapshot, -i NAME for a service microVM

Without -s, the disk is kept in out/run: the account made at first boot stays. Bad options are refused (tested).

How to verify

The boot report must say tcp=0 udp=0: nothing listens. Then make bench-boot times the boot: 20 boots per VMM, median and p95.

How to undo

Stop QEMU with Ctrl+C, or Firecracker by ending its process. snapshot=on leaves the qcow2 unchanged. Delete root.raw to drop the Firecracker disk.

See also

• Run the VM image
• On-premise AI
• Building x0ne OS from source