Tailvisor

macOS and Linux VM sandbox with a Tailscale network identity. Runs guest VMs using Apple's Virtualization.framework where all networking is routed through a tsnet node on the host. The VM appears on your tailnet as its own device — no Tailscale installed inside the guest.

How it works

┌─────────────────────────────────────────────┐
│              Tailvisor                      │
│                                             │
│   Swift (Virtualization.framework)          │
│     VM lifecycle, GUI window                │
│     macOS or Linux guest                    │
│              │                              │
│              │ VZFileHandleNetworkDevice    │
│              │ (Unix dgram socket)          │
│              ▼                              │
│   Go (linked as c-archive)                  │
│     ARP / DHCP / DNS / ICMP                 │
│     gVisor TCP stack → tsnet.Dial           │
│     UDP proxy → tsnet.Dial                  │
│              │                              │
└─────────────────────────────────────────────┘
               │
               │ WireGuard
               ▼
          your tailnet

This is a single binary. The Go networking code is compiled as a C archive (go build -buildmode=c-archive) and linked into the Swift executable.

The Go layer:

• Connects to Tailscale via tsnet.Server (each VM is its own Tailscale node)
• Reads raw ethernet frames from the VM via a Unix datagram socket
• Handles ARP, DHCP (assigns 192.168.72.2, gateway/DNS at 192.168.72.1), and ICMP echo
• Forces all VM egress that isn't a direct peer through an auto-selected exit node on the VM's tailnet (AutoExitNode = "any"), and pins tsdial.UseNetstackForIP on so no dial can fall back to the host's network stack.
• Resolves DNS: Tailscale peer names via LocalClient().Status(), everything else forwarded through tsnet's MagicDNS (100.100.100.100:53 dialed via tsnet.Dial, which is routed through netstack and answered by the VM's own tailnet DNS config)
• Intercepts all TCP via a gVisor userspace stack and proxies each connection through tsnet.Dial
• Proxies UDP similarly
• Provides the tailnet's MagicDNS suffix as a DHCP search domain so bare peer names resolve (e.g. ssh myhost)

The VM's tailnet must have at least one usable exit node. If none is available, AutoExitNode installs a blackhole route and all non-peer traffic from the guest is dropped — the guest can still reach its own tailnet peers but has no internet. To explicitly override this, use --unsafe-allow-host-network

Requirements

• Apple Silicon Mac (arm64) — Virtualization.framework is arm64-only
• macOS 14+ (Sonoma)
• Xcode (for Swift compilation)
• Go 1.24+

Building

# Build the CLI tool
make all
# Build the GUI tool
make app

This runs three steps:

1. go build -buildmode=c-archive — compiles Go networking code into libnetd.a
2. swift build — compiles Swift CLI, links libnetd.a
3. codesign — signs with the virtualization entitlement

The single binary ends up in bin/tailvisor.

If swift build can't find Xcode, set DEVELOPER_DIR:

DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer make all

Swift-only changes don't rebuild the Go archive (Make tracks .go file timestamps).

Usage

macOS VMs

# Create a VM (downloads macOS IPSW automatically on first run, ~13 GB)
bin/tailvisor create

# Run with a Tailscale auth key on first start
bin/tailvisor run --auth-key tskey-auth-...

# Later, just:
bin/tailvisor run

Linux VMs

# Create a Linux VM (requires an ARM64 installer ISO, e.g. Ubuntu Server)
bin/tailvisor create --os linux --name mylinux --iso ~/Downloads/ubuntu-24.04-live-server-arm64.iso

# Run — the first boot will start the ISO installer
bin/tailvisor run --name mylinux --auth-key tskey-auth-...

# After installation, subsequent boots go straight to the installed system
bin/tailvisor run --name mylinux

Linux VMs use UEFI boot (VZEFIBootLoader). On first boot with an empty disk, the firmware boots from the installer ISO (attached as USB mass storage). After installation, GRUB takes priority in the UEFI boot order and the installed system boots directly. The installer ISO is automatically ejected when the guest shuts down, so subsequent boots go straight to the installed system.

Common options

# Named VMs
bin/tailvisor create --name foo
bin/tailvisor run --name foo
bin/tailvisor ls
bin/tailvisor delete --name myvm

# Port forwarding
bin/tailvisor run --forward 2222:22

# Shared directories (virtiofs)
bin/tailvisor run --dir /path/to/share,tag=myshare

The VM window supports full keyboard and trackpad/mouse input. Closing the window (or Ctrl-C in CLI mode) saves VM state for fast resume on next run.

Shared directories

Shared directories use virtiofs. The mount command differs by guest OS:

macOS guest:

sudo mkdir -p /some/dire
mount_virtiofs myshare /some/dir

Note that directories may need to be remounted after a full stop and inodes will go stale after a pause/restart.

Linux guest:

sudo mkdir -p /mnt/myshare
sudo mount -t virtiofs myshare /mnt/myshare

VM storage

macOS VM layout

~/VM.bundle/
├── RestoreImage.ipsw              # shared macOS restore image
└── myvm/
    ├── config.json                # VM configuration (guestOS: "macos")
    ├── Disk.img                   # 128 GB sparse disk
    ├── AuxiliaryStorage
    ├── HardwareModel
    ├── MachineIdentifier
    ├── SaveFile.vzvmsave          # saved state (when stopped)
    └── tsnet/                     # tsnet state (own Tailscale identity)
        └── tailscaled.state

Linux VM layout

~/VM.bundle/
├── LinuxInstaller.iso             # shared Linux installer ISO
└── mylinux/
    ├── config.json                # VM configuration (guestOS: "linux")
    ├── Disk.img                   # 64 GB sparse disk
    ├── EFIVariableStore           # UEFI NVRAM
    ├── SaveFile.vzvmsave          # saved state (when stopped)
    └── tsnet/                     # tsnet state (own Tailscale identity)
        └── tailscaled.state

Network details

• TCP: intercepted via gVisor, proxied through tsnet.Dial("tcp", ...) (routed via the VM's own WireGuard tunnel — to a peer if it matches, or otherwise via the auto-selected exit node; never via the host stack)
• UDP: proxied through tsnet.Dial("udp", ...) on the same routing
• DNS: Tailscale peers resolved from status; everything else forwarded to 100.100.100.100:53 via tsnet.Dial, handled by tsnet's netstack MagicDNS and scoped to the VM's tailnet DNS config
• ICMP: echo reply for the gateway only; ping to external hosts is not proxied
• IPv6: not yet supported

Architecture

The Go networking code lives in netd/ and is compiled as a C archive (-buildmode=c-archive), producing libnetd.a. This is linked into the Swift executable via a SPM C target (CNetd). Three functions are exported across the boundary:

• goNetdStart(socketPath, tsnetDir, hostname, authKey, ephemeral) — starts the networking daemon in a background goroutine
• goNetdStop() — shuts it down
• goNetdReady() — returns 1 when the socket is listening

The Swift side (swift/) handles VM lifecycle via Virtualization.framework, the GUI window with VZVirtualMachineView, and the CLI via swift-argument-parser.