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

•Screenshot — Always start by seeing the screen
•Analyze — Identify UI elements and coordinates
•Act — Click, type, scroll
•Screenshot — Verify result
•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:

code

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

code

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
google-chrome --no-sandbox &    # Chrome (recommended)
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

# Copy service files
sudo cp systemd/*.service /etc/systemd/system/

# Edit xfce-minimal.service: replace %USER% and %SCRIPT_PATH%
sudo nano /etc/systemd/system/xfce-minimal.service

# Mask xfdesktop (prevents VNC flickering)
sudo mv /usr/bin/xfdesktop /usr/bin/xfdesktop.real
echo -e '#!/bin/bash\nexit 0' | sudo tee /usr/bin/xfdesktop
sudo chmod +x /usr/bin/xfdesktop

# Enable and start
sudo systemctl daemon-reload
sudo systemctl enable --now xvfb xfce-minimal x11vnc novnc

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