bsdkrun (Ruby SDK)

A Ruby SDK for bsdkrun — a Firecracker-style microVM launcher for BSD, Linux, and unikernel guests on macOS and Linux, built on libkrun. Boot and drive microVMs programmatically, inspired by the Vercel and Deno Sandbox SDKs.

The SDK shells out to the bsdkrun binary, so it has zero runtime dependencies — just the Ruby standard library (open3, json, pathname).

require "bsdkrun"

sbx = Bsdkrun::Sandbox.create(os: "linux", image: "alpine")

# exec argv directly, with env / stdin / a PTY / a working dir:
puts sbx.exec(["uname", "-a"]).text
sbx.exec(["apk", "add", "curl"], throw_on_error: true)
sbx.run_command("curl", ["-fsSL", "https://example.com"])

sbx.stop

Install

gem install bsdkrun

Or in a Gemfile:

gem "bsdkrun"

The bsdkrun binary

You need the bsdkrun binary itself. The SDK finds it via, in order:

1. Bsdkrun.binary_path = "/path/to/bsdkrun"
2. the BSDKRUN_BIN environment variable
3. bsdkrun on your PATH
4. an in-repo target/release/bsdkrun or target/debug/bsdkrun build

See the bsdkrun README for installing the binary (Homebrew on macOS, or build from source on Linux/KVM). This SDK assumes libkrun is already linked — it does not auto-provision it.

Creating a sandbox

Sandbox.create is discriminated on os: — the options change per guest kind. Pass keyword arguments or a Hash.

# Linux OCI image (docker run-style)
Bsdkrun::Sandbox.create(
  os: "linux",
  image: "ghcr.io/owner/name:tag",
  cpus: 2,
  mem: 1024,
  volume: "web",                       # persistent CoW rootfs
  mounts: ["~/project:/src", "~/data:/data:ro"],
  net: { ports: ["8080:80", "2222:22"] },
  command: ["node", "server.js"]       # args after `--`
)

# FreeBSD (EFI on macOS, PVH on Linux/amd64)
Bsdkrun::Sandbox.create(os: "freebsd", version: "14.3", mem: 2048)

# NetBSD (direct-kernel boot everywhere)
Bsdkrun::Sandbox.create(os: "netbsd", version: "10.1", volume: "db")

# Boot a raw disk through its UEFI loader
Bsdkrun::Sandbox.create(os: "firmware", firmware: "KRUN_EFI.fd", disk: "disk.raw")

# Boot a kernel directly, no bootloader
Bsdkrun::Sandbox.create(os: "kernel", kernel: "netbsd", format: "elf", disk: "root.raw")

Every create runs the machine detached and returns a Sandbox handle.

Environment variables

env: sets the guest environment for the machine's entrypoint. It is merged over the image's own config, so a key the image already defines is replaced rather than duplicated.

sbx = Bsdkrun::Sandbox.create(
  os: "linux",
  image: "node:22",
  env: { "NODE_ENV" => "production", "PORT" => "3000" },
  command: ["node", "server.js"]
)

Linux guests only — BSD guests boot their own init, so there is no generated init to export into; set those from exec after boot. For a single command rather than the whole machine, exec takes its own env:.

Running commands

exec is the primary programmatic entrypoint. No shell parsing — pass an argv array (or a program name plus args:).

sbx.exec(["ls", "-la", "/etc"])

sbx.exec("ruby",
  args: ["-e", "puts ENV['X']"],
  env: { "X" => "hi" },
  cwd: "/app",
  stdin: "data on stdin",
  tty: true,                 # allocate a PTY
  on_stdout: ->(chunk) { $stdout.write(chunk) },
  on_stderr: ->(chunk) { $stderr.write(chunk) },
  throw_on_error: true)      # raise on non-zero exit (default: false)

# Vercel-Sandbox-style alias:
result = sbx.run_command("uname", ["-a"])
result.stdout       # raw stdout
result.text         # stdout, trailing newlines trimmed
result.exit_code
result.ok?          # true on exit 0
result.lines        # non-empty stdout lines

exec returns a Bsdkrun::Result. It only raises CommandFailed when you pass throw_on_error: true (or call result.throw_if_failed!).

The callbacks run as chunks arrive, and the same bytes remain buffered in the returned result. They do not require tty; a PTY changes command semantics and may merge stderr into stdout.

Caching

sbx.cache saves a guest directory under a key and restores it later, so a rebuild can pick up where the last one left off. A miss is not an error — check restored rather than rescuing.

key = "deps-#{lock_hash}"
hit = sbx.cache.restore(key: key, restore_keys: ["deps-"])
unless hit.restored
  sbx.exec(["npm", "ci"])
  sbx.cache.save("/app/node_modules", key: key, compression: "zstd")
end

Bsdkrun::Caches.ls          # every stored entry, newest first
Bsdkrun::Caches.rm([key])   # or Bsdkrun::Caches.rm(all: true)

restore_keys are prefixes tried in order when the exact key misses; within a prefix the newest matching entry wins, and hit.key says which one was used. Formats are gzip (default), zstd, estargz and none.

Where entries live is host configuration, not an SDK concern: the default is this host's disk, and BSDKRUN_CACHE_BACKEND=s3 + BSDKRUN_CACHE_S3_* (or ~/.config/bsdkrun/cache.toml) points them at a bucket instead.

Files

sbx.fs reads and writes files in the guest. Parent directories are created for you, and everything is byte-exact — read_file returns a binary string.

sbx.fs.write_file("/app/main.py", "print('hi')")
sbx.fs.write_file("/app/logo.png", png_bytes)

text  = sbx.fs.read_text("/app/out.json")
bytes = sbx.fs.read_file("/app/logo.png")

sbx.fs.upload("./src", "/app/src")                       # file or directory
sbx.fs.download("/app/dist", "./dist", recursive: true)

upload looks at the local path to decide whether to recurse; download cannot (the path is in the guest), so say so for a directory. A directory's contents land in the destination: uploading ./src to /app/src leaves the guest's /app/src holding what ./src holds.

Failures raise Bsdkrun::FileTransferFailed, which carries the offending path.

Transfers ride the same in-guest agent as exec, so the sandbox must be running. A directory copy also needs tar in the guest; single files need only the shell every bootable image already has.

Lifecycle & inventory

sbx  = Bsdkrun::Sandbox.create(os: "linux", image: "alpine", command: ["sleep", "300"])
same = Bsdkrun::Sandbox.get(sbx.id)          # reconnect (prefix ok)
all  = Bsdkrun::Sandbox.list(all: true)      # Array<SandboxInfo>

sbx.status        # SandboxInfo | nil
sbx.running?      # true / false
sbx.logs          # console log (String)
sbx.shell         # interactive shell (inherits the terminal)
sbx.stop          # BSD guests clean-poweroff; Linux SIGTERM
sbx.start         # restart in place — resumes its own disk/rootfs (data persists)
sbx.update(cpus: 4, mem: 2048)               # applies on next start
sbx.remove(force: true)

Host-level namespaces:

Bsdkrun::System.probe                          # toolchain sanity check -> Boolean
Bsdkrun::Images.list                           # Array<ImageInfo>
Bsdkrun::Volumes.list                          # Array<VolumeInfo>
Bsdkrun::Volumes.remove("web", force: true)
Bsdkrun::Networks.list                         # Array<NetworkInfo>
Bsdkrun::System.fetch_image("freebsd", version: "14.3")
Bsdkrun::System.versions("netbsd")             # Array<String>

Networking, SSH & Tailscale

# forward ports at create time
Bsdkrun::Sandbox.create(os: "linux", image: "alpine", net: { ports: ["2222:22"] })

# agent-managed key-based SSH
sbx.ssh_setup                                  # install local ~/.ssh/*.pub keys
sbx.ssh_setup(user: "tsiry", key: "~/.ssh/work.pub")

# put a guest on your tailnet
sbx.tailscale_up(authkey: "tskey-auth-...", hostname: "web")

Global networks — reach machines by name

Opt machines into a shared network so they get distinct IPs on one subnet and reach each other by IP and by name (docker-compose style), with internal DNS:

require "bsdkrun"

Bsdkrun::Networks.create("devnet")

db = Bsdkrun::Sandbox.create(
  os: "linux", image: "alpine", name: "db",
  net: { network: "devnet" }, command: ["sleep", "3600"]
)
api = Bsdkrun::Sandbox.create(
  os: "linux", image: "alpine", name: "api",
  net: { network: "devnet" }, command: ["sleep", "3600"]
)

# api reaches db by name over the shared subnet
api.exec(["ping", "-c1", "db"], throw_on_error: true)

# inspect + manage
Bsdkrun::Networks.list                # Array<NetworkInfo>
Bsdkrun::Networks.members("devnet")   # Array<SandboxInfo> on the network
info = db.status                      # info.network == "devnet", info.net_ip set

# edit membership (applies on next start — a VM's NIC is fixed at boot)
api.connect_network("devnet")         # or Bsdkrun::Networks.connect(api.id, "devnet")
api.disconnect_network
api.start                             # re-joins with the new membership

Bsdkrun::Networks.sync("devnet")      # refresh members' /etc/hosts (fixes NetBSD name lookup)
Bsdkrun::Networks.remove("devnet", force: true)

Names resolve on Linux and FreeBSD via the network's DNS; NetBSD resolves via a synced /etc/hosts block — joins auto-sync, and Networks.sync refreshes an existing network without restarting members.

Connecting to a remote daemon

Everything above talks to a local bsdkrun binary. Bsdkrun::Client is the network sibling: it drives the same operations against a remote bsdkrund over its GraphQL API — no local binary needed, just a URL and a bearer token.

require "bsdkrun"

client = Bsdkrun::Client.new(url: "http://vps.example.com:50052", token: "9f2c...")
# or, from BSDKRUN_URL / BSDKRUN_TOKEN:
client = Bsdkrun::Client.from_env

machines = client.list(all: true)  # Array<SandboxInfo> — same type Sandbox.list returns
id = client.run_linux(image: "alpine", cpus: 2, mem: 1024, command: ["sleep", "300"])

result = client.exec(id, ["uname", "-a"])
puts result.output, result.exit_code

client.stop(id)
client.remove([id])

client.run_linux/run_bsd/run_nanos/run_unikraft/run_solo5/run_osv/ run_flavor each take the same options as the corresponding GraphQL mutation (daemon/src/graphql.rs) — run_bsd(os: "freebsd", ...), etc. — and return the new machine's id. run_solo5 boots a MirageOS unikernel under the solo5-hvt tender rather than libkrun: run_solo5(path: "dist/hello.hvt", args: ["--ipv4=10.0.0.2/24"]). stop/start/remove/update/commit return a CommandResult (exit_code, stdout, stderr).

For a live terminal instead of a one-shot exec, use shell:

session = client.shell(id)  # or shell(id, command: [...]) for a non-login command
session.on_output { |bytes| $stdout.write(bytes) }
session.on_exit { |code| puts "\nexited #{code}" }
session.write("ls -la\n")
session.resize(50, 120)
session.close

follow_logs(id) { |bytes| ... } streams a machine's console live instead of the one-shot logs(id). Both exec/shell and follow_logs are built on the same openShell/shellOutput shell-session protocol the daemon uses for every interactive terminal — see daemon/README.md for the wire-level story.

Not every GraphQL operation has a typed method yet (flavor/network/volume management, for instance) — client.request(query, variables) runs any raw query or mutation, and client.subscribe(query, variables, on_next: ...) runs any raw subscription, for anything not wrapped above.

Like the rest of this gem, Client uses only the Ruby standard library — the HTTP transport is Net::HTTP, and subscriptions (used by exec/shell/ follow_logs) run over a hand-rolled graphql-transport-ws client on top of Socket/OpenSSL, since Ruby's standard library has no WebSocket client of its own.

Client.new(url:, token:) and .from_env both reject a URL configured without a token rather than silently making an unauthenticated request — set both BSDKRUN_URL and BSDKRUN_TOKEN, or pass both explicitly.

Errors

All errors extend Bsdkrun::Error:

• Bsdkrun::BinaryNotFound — the bsdkrun binary wasn't found.
• Bsdkrun::CommandFailed — a command exited non-zero (carries exit_code, stdout, stderr, command). Raised by exec with throw_on_error: true, by the lifecycle/namespace helpers, and by the agent helpers.
• Bsdkrun::SandboxNotFound — Sandbox.get matched no machine.
• Bsdkrun::GraphQLError — a Client request failed (carries code, the daemon's extensions.code, when there is one).
• Bsdkrun::AuthError (a GraphQLError) — the daemon rejected the bearer token.

Try it interactively

bin/console

Starts IRB with the SDK preloaded — Bsdkrun::Sandbox, the Bsdkrun.images / .volumes / .networks / .system namespaces, plus ps (every machine, exited ones included) and last (the newest one). Pass --bin ../../target/release/bsdkrun to drive a locally built binary for the session.

License

MIT