Computer Use

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):

./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

Usage Examples

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

# 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

# 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

# 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

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:

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:

# 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:

xvfb xfce4 xfce4-terminal xdotool scrot imagemagick dbus-x11 x11vnc novnc websockify