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Interactive Desktop And VNC

Read when:

  • choosing a desktop target for browser or UI testing;
  • opening a lease with native VNC or the web portal (WebVNC);
  • diagnosing stale WebVNC viewers, bridge disconnects, or broken desktop sessions;
  • driving desktop input from automation without hand-written xdotool;
  • deciding which layer owns desktop setup, browser state, screenshots, or credentials.

Crabbox treats desktop access as a lease capability, not a separate remote access product. A desktop lease keeps the normal Crabbox boundaries: provider lifecycle, per-lease SSH keys, SSH tunnels, idle expiry, cleanup, and run history. VNC is one way to inspect or drive the visible session inside that boundary.

Quick Start

crabbox warmup --desktop --browser
crabbox webvnc --id blue-lobster --open
crabbox webvnc status --id blue-lobster
crabbox desktop doctor --id blue-lobster
crabbox vnc --id blue-lobster --open
crabbox screenshot --id blue-lobster --output desktop.png

AWS Windows and EC2 Mac use the same vnc command once the desktop lease exists:

crabbox warmup --provider aws --target windows --desktop
crabbox vnc --id crimson-crab --open

crabbox warmup --provider aws --target macos --desktop --market on-demand
crabbox vnc --id silver-squid --open

Static hosts are existing machines, so VNC against them is explicit and host-managed:

crabbox vnc --provider ssh --target macos --static-host mac-studio.local --host-managed --open
crabbox vnc --provider ssh --target windows --static-host win-dev.local --host-managed --open

What Crabbox Owns

Crabbox owns:

  • the lease lifecycle and cleanup;
  • per-lease SSH keys and known_hosts scoping;
  • SSH local forwarding to the target's loopback VNC service;
  • generated per-lease VNC or OS passwords for managed desktop leases;
  • desktop=true, browser=true, code=true, and desktop_env lease labels;
  • screenshots, video, and launch/input commands that run inside the lease.

A scenario layer on top of Crabbox owns:

  • product-specific login and app credentials;
  • browser profile import and export;
  • before/after screenshots that prove a bug and its fix;
  • PR comments, issue triage, and artifact summaries.

Support Matrix

Target Managed by Crabbox Desktop access Primary page
Linux on Hetzner Yes Xvfb/XFCE + x11vnc, or Wayland + WayVNC, over SSH tunnel Linux VNC
Linux on AWS Yes Xvfb/XFCE + x11vnc, or Wayland + WayVNC, over SSH tunnel Linux VNC
Linux on Azure Yes Xvfb/XFCE + x11vnc, or Wayland + WayVNC, over SSH tunnel Linux VNC
AWS Windows Yes VNC service over SSH tunnel Windows VNC
Azure Windows Yes VNC service over SSH tunnel Windows VNC
AWS EC2 Mac Yes Screen Sharing/VNC over SSH tunnel macOS VNC
Local Docker container Yes Loopback VNC over SSH tunnel Linux VNC
Static Linux Host-managed Existing loopback VNC service Linux VNC
Static macOS Host-managed Existing Screen Sharing/VNC macOS VNC
Static Windows Host-managed Existing VNC service Windows VNC
Blacksmith Testbox No Not exposed through Crabbox VNC Blacksmith Testbox

Desktop capabilities require a provider that advertises the desktop feature (crabbox providers lists support). Blacksmith and other connectivity-owning providers reject the desktop, VNC, screenshot, and input commands.

Choosing A Viewer

Two viewers share the same runner-side VNC service; they differ only in the local-to-portal path.

  • crabbox webvnc is the default for human demos and shared sessions. A local crabbox webvnc process keeps the SSH tunnel open, connects to the coordinator with a one-use bridge ticket, and the authenticated portal serves bundled noVNC. The portal never connects to the runner directly, so the local bridge must keep running. --open preloads the VNC password into the local browser fragment.
  • crabbox vnc is for a native VNC client: when WebVNC status or reset reports the portal path is unhealthy, or when you need a native client feature.
crabbox webvnc --id blue-lobster --open --take-control
crabbox webvnc status --id blue-lobster
crabbox webvnc reset --id blue-lobster --open --take-control

crabbox vnc --id blue-lobster
crabbox vnc --id blue-lobster --network tailscale
crabbox vnc --id blue-lobster --open

WebVNC is available on coordinator-managed desktop leases and on direct desktop providers. Direct providers normally use a localhost viewer. With broker.mode: registered, direct leases instead use the outbound coordinator bridge, so KubeVirt, external, static SSH, local Docker, and other SSH desktop leases can appear in and be shared from the portal. Blacksmith remains unsupported. Native crabbox vnc works against every managed and host-managed desktop in the support matrix.

For kept registered desktop leases, broker.autoWebVNC: true starts the bridge daemon automatically. The daemon heartbeats the registration while connected; crabbox stop stops it and removes the registration after provider cleanup. The portal defaults to the viewer's system appearance and sends the resolved light or dark theme through that bridge on connect and whenever the operating system appearance changes.

Collaborative WebVNC

The local bridge keeps a warm pool of backend VNC sessions (default 4 slots). The first browser viewer becomes the controller; later viewers join as read-only observers. Any viewer — a new observer or the previous controller — can press take over to become the controller; whoever loses control stays connected as an observer and sees who took over. Pass --take-control so the opened browser requests control immediately, which is useful for handoffs. Observer mode is meant for trusted shared leases; it is not a hostile-client security boundary.

The portal toolbar exchanges the clipboard explicitly. Paste reads the local browser clipboard, forwards it to the remote VNC server, and sends the target paste shortcut. Copy-remote becomes available once the remote server publishes clipboard text, then writes it to the local browser clipboard on click; browsers generally block fully automatic clipboard writes without a user gesture.

Capturing Without Taking Over

Use crabbox screenshot for a PNG without attaching to the session:

crabbox screenshot --id blue-lobster --output desktop.png

Screenshot capture is loopback-based: Linux uses grim (Wayland) or scrot/import (X11), macOS uses screencapture, and native Windows uses an interactive screen capture task. Static hosts only support screenshots on Linux targets, since macOS and Windows static hosts are existing machines.

For a durable proof bundle instead of a single image, use crabbox artifacts:

crabbox artifacts collect --id blue-lobster --all --output artifacts/blue-lobster
crabbox artifacts publish --dir artifacts/blue-lobster --pr 123 --storage s3 --bucket qa-artifacts

See the artifacts feature doc and the artifacts command reference for bundle contents and publish targets.

Launching Apps And Terminals

crabbox desktop launch starts a browser or app inside the visible session without keeping the SSH command attached:

crabbox desktop launch --id blue-lobster --browser --url https://example.com --webvnc --open --take-control

For human demos, launched browsers stay windowed so the desktop panel, title bar, and surrounding session remain visible. Use --fullscreen only when you want browser-only video or capture output. --webvnc (and its --open / --take-control companions) bridges the launched desktop into the portal and requires a coordinator-backed Hetzner, AWS, or Azure lease. The local container provider uses local noVNC over SSH. --egress routes the launched browser through the lease-local egress proxy (default 127.0.0.1:3128) and currently requires --browser; see mediated egress.

crabbox desktop terminal starts a visible terminal and can capture a screenshot or record video after a short visibility delay:

crabbox desktop terminal --id blue-lobster --cols 120 --rows 40 -- npm test
crabbox desktop terminal --id blue-lobster --record run.mp4 --record-duration 8s

crabbox desktop proof launches a terminal and collects a full proof directory (metadata, screenshot, diagnostics, video, contact sheet), with optional publish flags. crabbox desktop record records desktop video (an alias for artifacts video). Video capture currently requires an X11 Linux desktop or a native Windows desktop; Wayland desktop envs are rejected for video.

Desktop Doctor

Run crabbox desktop doctor --id <lease> before blaming WebVNC. On Linux it checks the desktop session, VNC service, input tooling, browser binary, ffmpeg, screen geometry, and screenshot capture, layer by layer, then separately reports the portal's WebVNC bridge and viewer status with one-line repair suggestions.

Desktop and WebVNC commands are built for rescue-first debugging. When a command cannot prove the expected state it prints the failing layer (for example problem: browser not launched, problem: input stack dead, problem: VNC bridge disconnected, problem: WebVNC daemon not running) followed by an exact rescue: command. webvnc status and webvnc reset also print the exact native crabbox vnc ... --open fallback when the native viewer is the better next step, preserving any explicit --network public or --network tailscale selection.

Driving Input

Use the first-class input helpers instead of hand-rolled xdotool:

crabbox desktop click --id blue-lobster --x 640 --y 420
crabbox desktop paste --id blue-lobster --text "alice@example.com"
printf 'alice@example.com' | crabbox desktop paste --id blue-lobster
crabbox desktop type --id blue-lobster --text "hello"
crabbox desktop key --id blue-lobster ctrl+l
crabbox desktop key blue-lobster ctrl+l
  • desktop click works on managed Linux, macOS, and native Windows targets.
  • Prefer desktop paste or desktop type for emails, passwords, URLs, and any text with characters such as @ or +; raw key-symbol typing can vary with the target keyboard layout. desktop type automatically falls back to a paste for special characters, newlines, or long text.
  • desktop key is for shortcuts and special keys, and accepts both --id <lease> <keys> and the positional <lease> <keys> form.

Input helpers other than click currently target Linux desktops. On X11 they use xdotool and xclip/xsel; on Wayland/GNOME desktop leases they use wtype and wl-clipboard.

Network Model

Managed VNC is tunnel-first:

  • VNC binds to 127.0.0.1:5900 on the target.
  • The cloud firewall or security group opens SSH only, not VNC.
  • crabbox vnc forwards a local port (the first free port in 5901–5999) to remote 127.0.0.1:5900.
  • --network tailscale changes only the SSH endpoint used by that tunnel.
  • Remote-host providers such as Parallels carry their SSH proxy command into VNC, screenshots, and input commands using the same tunnel model.
  • WebVNC keeps the same local SSH tunnel and adds an authenticated browser websocket through the coordinator. Browser websockets are paired with local bridge backend sessions inside the coordinator Durable Object: one viewer is the controller, the rest are observers until they take over. If a browser view disconnects, only its paired backend session resets, and the local command reconnects a fresh bridge slot for the next portal retry.
  • crabbox webvnc status reports the local daemon pid and log, the SSH tunnel command, target VNC reachability, the coordinator bridge and viewer state, recent bridge events, the portal URL and password, and the exact native crabbox vnc ... --open fallback.
  • crabbox webvnc reset closes only the selected lease's WebVNC sockets, stops only that lease's verified local WebVNC daemon, restarts the target desktop and VNC services, then prints a fresh portal URL.

Crabbox never binds managed VNC directly to a public IP or a Tailscale 100.x address. Static hosts can expose a direct host:5900 endpoint only when the operator has already made it reachable on a trusted network; crabbox vnc falls back to that direct endpoint only when the SSH loopback service is unreachable.

Running WebVNC As A Daemon

For long-lived sessions, run the bridge in the background:

crabbox webvnc daemon start --id blue-lobster --open
crabbox webvnc daemon status --id blue-lobster
crabbox webvnc daemon stop --id blue-lobster

The compatibility flags --daemon/--background, --status, and --stop map to daemon start, daemon status, and daemon stop respectively.

Browser State

--browser guarantees a browser binary and env such as BROWSER and CHROME_BIN; it does not create, unlock, sync, or migrate a logged-in profile. On managed Linux leases these env vars point to a Crabbox wrapper that disables Chrome/Chromium first-run and default-browser prompts and pins a per-lease profile for repeatable VNC use. Manual browser login through VNC lasts only for that lease unless you intentionally export an artifact. On static hosts, any existing browser profile belongs to that host.

For repeatable logged-in tests, prefer scenario-owned state such as a Playwright storage-state file or a short-lived app token. Avoid syncing full browser profile directories between operating systems; browser credentials are often machine- and user-encrypted.

Security Rules

  • Never expose managed VNC directly to the public internet.
  • Do not expose managed VNC directly on a Tailscale interface.
  • Prefer SSH local forwarding such as localhost:5901 -> 127.0.0.1:5900.
  • Generate per-lease passwords for managed desktop leases.
  • Redact passwords from logs, provider metadata, and run records.
  • Keep TTL and idle-timeout cleanup in force.
  • Require --host-managed before opening static-host VNC prompts.

Where To Go Next

  • Linux VNC: Hetzner/AWS/Azure Linux desktop services and static Linux.
  • Windows VNC: AWS/Azure managed Windows, native Windows static hosts, and WSL2 boundaries.
  • macOS VNC: AWS EC2 Mac and static Mac Screen Sharing.
  • Capabilities: how --desktop, --browser, and --code are requested and validated.
  • Portal: the authenticated web UI that hosts WebVNC and Code panes.
  • Mediated egress: per-app browser/app egress through the operator machine.
  • AWS: AWS target matrix, capacity, AMIs, and EC2 Mac host requirements.
  • Hetzner: Linux-only managed Hetzner behavior.
  • Blacksmith Testbox: delegated Testbox behavior and why VNC is not a Crabbox feature there.
  • Command references: vnc, webvnc, screenshot, desktop, artifacts, egress.