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Backends

Cleanroom runs Linux microVMs on both Linux and macOS. The public CLI and policy surface is the same; backend-specific details live in runtime config and adapter internals.

Host OS Backend Notes
Linux firecracker KVM-backed microVMs, per-sandbox TAP devices, host firewall egress enforcement, file-backed or ZFS-backed snapshots
macOS darwin-vz Apple Virtualization.framework microVMs, filehandle networking, TCP egress filtering, APFS snapshots when supported

Choosing A Backend

The default backend is chosen for the host OS. Override it in runtime config:

default_backend: darwin-vz

Or for one command:

cleanroom exec --backend firecracker -- uname -a

Linux

The Linux backend uses Firecracker and KVM. Host setup needs:

  • Firecracker binary
  • Linux kernel image and rootfs configured in runtime config
  • helper support for host networking and snapshot operations
  • iptables support for egress enforcement

firecracker supports deny-by-default allowlist egress. Stage-scoped network policies currently fail closed on this backend.

See Firecracker Backend for details.

macOS

The macOS backend uses a signed Swift helper built on Virtualization.framework. Host setup needs:

  • cleanroom-darwin-vz helper
  • kernel and rootfs assets
  • mkfs.ext4 and debugfs from e2fsprogs

darwin-vz supports filehandle TCP egress filtering and stage-scoped network policies. It does not expose Firecracker-style TAP devices or host-visible guest IP identity.

See Darwin VZ Backend for details.

Capabilities

Run:

cleanroom doctor
cleanroom doctor --json

Doctor reports backend availability, required host tools, snapshot support, and capability gaps for the current runtime config.