Computer Use

---
name: computer-use
description: Full desktop computer use for headless Linux servers. Xvfb + XFCE virtual desktop with xdotool automation. 17 actions (click, type, scroll, screenshot, drag, etc). Unlike OpenClaw's browser tool, operates at the X11 level so websites cannot detect automation. Includes VNC for live viewing.
version: 1.2.1
---

# Computer Use Skill

Full desktop GUI control for headless Linux servers. Creates a virtual display (Xvfb + XFCE) so you can run and control desktop applications on VPS/cloud instances without a physical monitor.

## Environment

- **Display**: `:99`
- **Resolution**: 1024x768 (XGA, Anthropic recommended)
- **Desktop**: XFCE4 (minimal — xfwm4 + panel only)

## Quick Setup

Run the setup script to install everything (systemd services, flicker-free VNC):

```bash
./scripts/setup-vnc.sh
```

This installs:
- Xvfb virtual display on `:99`
- Minimal XFCE desktop (xfwm4 + panel, no xfdesktop)
- x11vnc with stability flags
- noVNC for browser access

All services auto-start on boot and auto-restart on crash.

## Actions Reference

| Action | Script | Arguments | Description |
|--------|--------|-----------|-------------|
| screenshot | `screenshot.sh` | — | Capture screen → base64 PNG |
| cursor_position | `cursor_position.sh` | — | Get current mouse X,Y |
| mouse_move | `mouse_move.sh` | x y | Move mouse to coordinates |
| left_click | `click.sh` | x y left | Left click at coordinates |
| right_click | `click.sh` | x y right | Right click |
| middle_click | `click.sh` | x y middle | Middle click |
| double_click | `click.sh` | x y double | Double click |
| triple_click | `click.sh` | x y triple | Triple click (select line) |
| left_click_drag | `drag.sh` | x1 y1 x2 y2 | Drag from start to end |
| left_mouse_down | `mouse_down.sh` | — | Press mouse button |
| left_mouse_up | `mouse_up.sh` | — | Release mouse button |
| type | `type_text.sh` | "text" | Type text (50 char chunks, 12ms delay) |
| key | `key.sh` | "combo" | Press key (Return, ctrl+c, alt+F4) |
| hold_key | `hold_key.sh` | "key" secs | Hold key for duration |
| scroll | `scroll.sh` | dir amt [x y] | Scroll up/down/left/right |
| wait | `wait.sh` | seconds | Wait then screenshot |
| zoom | `zoom.sh` | x1 y1 x2 y2 | Cropped region screenshot |

## Usage Examples

```bash
export DISPLAY=:99

# Take screenshot
./scripts/screenshot.sh

# Click at coordinates
./scripts/click.sh 512 384 left

# Type text
./scripts/type_text.sh "Hello world"

# Press key combo
./scripts/key.sh "ctrl+s"

# Scroll down
./scripts/scroll.sh down 5
```

## Workflow Pattern

1. **Screenshot** — Always start by seeing the screen
2. **Analyze** — Identify UI elements and coordinates
3. **Act** — Click, type, scroll
4. **Screenshot** — Verify result
5. **Repeat**

## Tips

- Screen is 1024x768, origin (0,0) at top-left
- Click to focus before typing in text fields
- Use `ctrl+End` to jump to page bottom in browsers
- Most actions auto-screenshot after 2 sec delay
- Long text is chunked (50 chars) with 12ms keystroke delay

## Live Desktop Viewing (VNC)

Watch the desktop in real-time via browser or VNC client.

### Connect via Browser

```bash
# SSH tunnel (run on your local machine)
ssh -L 6080:localhost:6080 your-server

# Open in browser
http://localhost:6080/vnc.html
```

### Connect via VNC Client

```bash
# SSH tunnel
ssh -L 5900:localhost:5900 your-server

# Connect VNC client to localhost:5900
```

### SSH Config (recommended)

Add to `~/.ssh/config` for automatic tunneling:

```
Host your-server
  HostName your.server.ip
  User your-user
  LocalForward 6080 127.0.0.1:6080
  LocalForward 5900 127.0.0.1:5900
```

Then just `ssh your-server` and VNC is available.

## System Services

```bash
# Check status
systemctl status xvfb xfce-minimal x11vnc novnc

# Restart if needed
sudo systemctl restart xvfb xfce-minimal x11vnc novnc
```

### Service Chain

```
xvfb → xfce-minimal → x11vnc → novnc
```

- **xvfb**: Virtual display :99 (1024x768x24)
- **xfce-minimal**: Watchdog that runs xfwm4+panel, kills xfdesktop
- **x11vnc**: VNC server with `-noxdamage` for stability
- **novnc**: WebSocket proxy with heartbeat for connection stability

## Opening Applications

```bash
export DISPLAY=:99

# Chrome — only use --no-sandbox if the kernel lacks user namespace support.
# Check: cat /proc/sys/kernel/unprivileged_userns_clone
#   1 = sandbox works, do NOT use --no-sandbox
#   0 = sandbox fails, --no-sandbox required as fallback
# Using --no-sandbox when unnecessary causes instability and crashes.
if [ "$(cat /proc/sys/kernel/unprivileged_userns_clone 2>/dev/null)" = "0" ]; then
    google-chrome --no-sandbox &
else
    google-chrome &
fi

xfce4-terminal &                # Terminal
thunar &                        # File manager
```

**Note**: Snap browsers (Firefox, Chromium) have sandbox issues on headless servers. Use Chrome `.deb` instead:

```bash
wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
sudo dpkg -i google-chrome-stable_current_amd64.deb
sudo apt-get install -f
```

## Manual Setup

If you prefer manual setup instead of `setup-vnc.sh`:

```bash
# Install packages
sudo apt install -y xvfb xfce4 xfce4-terminal xdotool scrot imagemagick dbus-x11 x11vnc novnc websockify

# Run the setup script (generates systemd services, masks xfdesktop, starts everything)
./scripts/setup-vnc.sh
```

If you prefer fully manual setup, the `setup-vnc.sh` script generates all systemd service files inline -- read it for the exact service definitions.

## Troubleshooting

### VNC shows black screen
- Check if xfwm4 is running: `pgrep xfwm4`
- Restart desktop: `sudo systemctl restart xfce-minimal`

### VNC flickering/flashing
- Ensure xfdesktop is masked (check `/usr/bin/xfdesktop`)
- xfdesktop causes flicker due to clear→draw cycles on Xvfb

### VNC disconnects frequently
- Check noVNC has `--heartbeat 30` flag
- Check x11vnc has `-noxdamage` flag

### x11vnc crashes (SIGSEGV)
- Add `-noxdamage -noxfixes` flags
- The DAMAGE extension causes crashes on Xvfb

## Requirements

Installed by `setup-vnc.sh`:
```bash
xvfb xfce4 xfce4-terminal xdotool scrot imagemagick dbus-x11 x11vnc novnc websockify
```