Show HN: Smol machines – subsecond coldstart, portable virtual machines

Ship and run software with isolation by default.

This is a CLI tool that lets you:

1. Manage and run custom Linux virtual machines locally with: sub-second cold start, cross-platform (macOS, Linux), elastic memory usage.
2. Pack a stateful virtual machine into a single file (.smolmachine) to rehydrate on any supported platform.

Install

# install (macOS + Linux)
curl -sSL https://smolmachines.com/install.sh | bash

# for coding agents — install + discover all commands
curl -sSL https://smolmachines.com/install.sh | bash && smolvm --help

Or download from GitHub Releases.

Quick Start

# run a command in an ephemeral VM (cleaned up after exit)
smolvm machine run --net --image alpine -- sh -c "echo 'Hello world from a microVM' && uname -a"

# interactive shell
smolvm machine run --net -it --image alpine -- /bin/sh
# inside the VM: apk add sl && sl && exit

Use This For

Sandbox untrusted code — run untrusted programs in a hardware-isolated VM. Host filesystem, network, and credentials are separated by a hypervisor boundary.

# network is off by default — untrusted code can't phone home
smolvm machine run --image alpine -- ping -c 1 1.1.1.1
# fails — no network access

# lock down egress — only allow specific hosts
smolvm machine run --net --image alpine --allow-host registry.npmjs.org -- wget -q -O /dev/null https://registry.npmjs.org
# works — allowed host

smolvm machine run --net --image alpine --allow-host registry.npmjs.org -- wget -q -O /dev/null https://google.com
# fails — not in allow list

Pack into portable executables — turn any workload into a self-contained binary. All dependencies are pre-baked — no install step, no runtime downloads, boots in <200ms.

smolvm pack create --image python:3.12-alpine -o ./python312
./python312 run -- python3 --version
# Python 3.12.x — isolated, no pyenv/venv/conda needed

Persistent machines for development — create, stop, start. Installed packages survive restarts.

smolvm machine create --net myvm
smolvm machine start --name myvm
smolvm machine exec --name myvm -- apk add sl
smolvm machine exec --name myvm -it -- /bin/sh
# inside: sl, ls, uname -a — type 'exit' to leave
smolvm machine stop --name myvm

Use git and SSH without exposing keys — forward your host SSH agent into the VM. Private keys never enter the guest — the hypervisor enforces this. Requires an SSH agent running on your host (ssh-add -l to check).

smolvm machine run --ssh-agent --net --image alpine -- sh -c "apk add -q openssh-client && ssh-add -l"
# lists your host keys, but they can't be extracted from inside the VM

smolvm machine exec --name myvm -- git clone git@github.com:org/private-repo.git

Declare environments with a Smolfile — reproducible VM config in a simple TOML file.

image = "python:3.12-alpine"
net = true

[network]
allow_hosts = ["api.stripe.com", "db.example.com"]

[dev]
init = ["pip install -r requirements.txt"]
volumes = ["./src:/app"]

[auth]
ssh_agent = true

smolvm machine create myvm -s Smolfile
smolvm machine start --name myvm

More examples: python · node · doom

How It Works

Each workload gets real hardware isolation — its own kernel on Hypervisor.framework (macOS) or KVM (Linux). libkrun VMM with custom kernel: libkrunfw. Pack it into a .smolmachine and it runs anywhere the host architecture matches, with zero dependencies.

Defaults: 4 vCPUs, 8 GiB RAM. Memory is elastic via virtio balloon — the host only commits what the guest actually uses and reclaims the rest automatically. vCPU threads sleep in the hypervisor when idle, so over-provisioning has near-zero cost. Override with --cpus and --mem.

Comparison

Platform Support

Known Limitations

• Network is opt-in (--net on machine create). TCP/UDP only, no ICMP.
• Volume mounts: directories only (no single files).
• macOS: binary must be signed with Hypervisor.framework entitlements.
• --ssh-agent requires an SSH agent running on the host (SSH_AUTH_SOCK must be set).

Development

See docs/DEVELOPMENT.md.

Apache-2.0 · made by @binsquare · twitter · github