OpenShell/crates/openshell-vm

openshell-vm

Status: Experimental and work in progress (WIP). VM support is under active development and may change.

MicroVM runtime for OpenShell, powered by libkrun. Boots a lightweight ARM64 Linux VM on macOS (Apple Hypervisor.framework) or Linux (KVM) running a single-node k3s cluster with the OpenShell control plane.

Quick Start

# One-time setup: download pre-built runtime (~30s)
mise run vm:setup

# Build and run the VM
mise run vm

Prerequisites

• macOS (Apple Silicon) or Linux (aarch64 or x86_64 with KVM)
• Rust toolchain
• Guest-supervisor cross-compile toolchain (needed on macOS, and on Linux when host arch ≠ guest arch):
  • Matching rustup target: rustup target add aarch64-unknown-linux-gnu (or x86_64-unknown-linux-gnu for an amd64 guest)
  • cargo install --locked cargo-zigbuild and brew install zig (or distro equivalent). build-rootfs.sh uses cargo zigbuild to cross-compile the in-VM openshell-sandbox supervisor binary.
• mise task runner
• Docker (for rootfs builds)
• gh CLI (for downloading pre-built runtime)

macOS-Specific

The binary must be codesigned with the Hypervisor.framework entitlement. The mise run vm flow handles this automatically. To codesign manually:

codesign --entitlements crates/openshell-vm/entitlements.plist --force -s - target/debug/openshell-vm

Setup

Download Pre-Built Runtime (Default)

Downloads libkrun, libkrunfw, and gvproxy from the vm-dev GitHub Release:

mise run vm:setup

Build from Source

Compiles the runtime from source (15-45 minutes, needed for custom kernel work):

FROM_SOURCE=1 mise run vm:setup

On macOS this builds a custom libkrunfw (kernel firmware with bridge/netfilter support) via krunvm, then builds a portable libkrun. On Linux it builds both natively.

Build

Build the openshell-vm binary with embedded runtime:

mise run vm:build

This compresses runtime artifacts, compiles the Rust binary with include_bytes!() embedding, codesigns it (macOS), and stages the sidecar runtime bundle.

Rootfs

The rootfs is an Ubuntu filesystem containing k3s, pre-loaded container images, and the OpenShell binaries. Build it with:

# Base rootfs (~200-300MB, cold starts in ~30-60s)
mise run vm:rootfs -- --base

# Full rootfs (~2GB+, pre-initialized, boots in ~3-5s)
mise run vm:rootfs

Run

Default (Gateway Mode)

Boots the full OpenShell gateway -- k3s + openshell-server + openshell-sandbox:

mise run vm

Or run the binary directly:

./target/debug/openshell-vm

Custom Process

Run an arbitrary process inside a fresh VM instead of k3s:

./target/debug/openshell-vm --exec /bin/sh --vcpus 2 --mem 2048

Execute in a Running VM

Attach to a running VM and run a command:

./target/debug/openshell-vm exec -- ls /
./target/debug/openshell-vm exec -- sh   # interactive shell

Named Instances

Run multiple isolated VM instances side-by-side:

./target/debug/openshell-vm --name dev
./target/debug/openshell-vm --name staging

Each instance gets its own extracted rootfs under ~/.local/share/openshell/openshell-vm/<version>/instances/<name>/rootfs.

CLI Reference

openshell-vm [OPTIONS] [COMMAND]

Options:
  --rootfs <PATH>          Path to aarch64 Linux rootfs directory
  --name <NAME>            Named VM instance (auto-clones rootfs)
  --exec <PATH>            Run a custom process instead of k3s
  --args <ARGS>...         Arguments to the executable
  --env <KEY=VALUE>...     Environment variables
  --workdir <DIR>          Working directory inside the VM [default: /]
  -p, --port <H:G>...     Port mappings (host_port:guest_port)
  --vcpus <N>              Virtual CPUs [default: 4 gateway, 2 exec]
  --mem <MiB>              RAM in MiB [default: 8192 gateway, 2048 exec]
  --krun-log-level <0-5>   libkrun log level [default: 1]
  --net <BACKEND>          Networking: gvproxy, tsi, none [default: gvproxy]
  --reset                  Wipe runtime state before booting

Subcommands:
  prepare-rootfs           Ensure the target rootfs exists
  exec                     Execute a command inside a running VM

mise Tasks Reference

Task	Description
vm	Build and run the VM
vm:build	Build openshell-vm binary with embedded runtime
vm:setup	One-time setup: download (or build) the VM runtime
vm:rootfs	Build the VM rootfs tarball (-- --base for lightweight)
vm:clean	Remove all VM cached artifacts
e2e:vm	Boot VM and run smoke e2e tests

Common Workflows

# First time setup
mise run vm:setup              # download pre-built runtime (~30s)
mise run vm                    # build + run

# Day-to-day iteration
mise run vm                    # incremental build + run

# Need fresh rootfs
mise run vm:rootfs -- --base   # rebuild base rootfs
mise run vm:build              # rebuild binary with new rootfs

# Something broken, start over
mise run vm:clean              # wipe everything
mise run vm:setup              # re-download runtime
mise run vm                    # full rebuild + run

# Custom kernel work (rare)
FROM_SOURCE=1 mise run vm:setup

Architecture

Host (macOS / Linux)
  openshell-vm binary
    |-- Embedded runtime (libkrun, libkrunfw, gvproxy, rootfs.tar.zst)
    |-- FFI: loads libkrun at runtime via dlopen
    |-- gvproxy: virtio-net networking (real eth0 + DHCP)
    |-- virtio-fs: shares rootfs with guest
    \-- vsock: host-to-guest command execution (port 10777)

Guest VM (aarch64 Linux)
  PID 1: openshell-vm-init.sh
    |-- Mounts filesystems, configures networking
    |-- Sets up bridge CNI, generates PKI
    \-- Execs k3s server
        |-- openshell-server (gateway control plane)
        \-- openshell-sandbox (pod supervisor)

Environment Variables

Variable	When	Purpose
OPENSHELL_VM_RUNTIME_COMPRESSED_DIR	Build time	Path to compressed runtime artifacts
OPENSHELL_VM_RUNTIME_DIR	Runtime	Override the runtime bundle directory
OPENSHELL_VM_DIAG=1	Runtime	Enable diagnostic output inside the VM
FROM_SOURCE=1	vm:setup	Build runtime from source instead of downloading

Custom Kernel (libkrunfw)

The stock libkrunfw (e.g. from Homebrew) lacks bridge, netfilter, and conntrack support needed for pod networking. OpenShell builds a custom libkrunfw with these enabled.

Build it via the setup command:

FROM_SOURCE=1 mise run vm:setup

See runtime/README.md for details on the kernel config and troubleshooting.

Testing

Integration tests require a built rootfs and macOS ARM64 with libkrun:

cargo test -p openshell-vm -- --ignored

Individual tests:

# Full gateway boot test (boots VM, waits for gRPC on port 30051)
cargo test -p openshell-vm gateway_boots -- --ignored

# Run a command inside the VM
cargo test -p openshell-vm gateway_exec_runs -- --ignored

# Exec into a running VM
cargo test -p openshell-vm gateway_exec_attaches -- --ignored

Verify kernel capabilities inside a running VM:

./target/debug/openshell-vm exec -- /srv/check-vm-capabilities.sh
./target/debug/openshell-vm exec -- /srv/check-vm-capabilities.sh --json