Capture Screen Linux

Screen Capture Skill (Linux)

Capabilities

• Take full screen screenshots.
• Take screenshots of specific application windows (e.g., Browsers like Firefox, Chrome, Browsers).
• Get information about the currently active window or list all windows.

Best Practices

⚠️ IMPORTANT: Before taking a window-specific screenshot, ALWAYS list all available windows first to identify the correct window name. Window class names and titles can vary across different desktop environments and applications.

Recommended Workflow:

1. Run python3 capture-screen-linux/window_info.py list to see all available windows
2. Identify the window by its app name or title from the JSON output
3. Use that app name or title in the screenshot command

Usage

1. Get Window Information (CRITICAL FIRST STEP)

⭐ ALWAYS START HERE when capturing specific windows to avoid errors.

List All Windows (Recommended): Returns a JSON array with all detected windows, including app name (WM_CLASS), window title, ID, bounds, and area.

python3 capture-screen-linux/window_info.py list

Example output:

[
  {
    "app": "Firefox",
    "title": "GitHub - example/repo - Mozilla Firefox",
    "id": 12345678,
    "bounds": {"X": 0, "Y": 25, "Width": 1920, "Height": 1055},
    "area": 2025600
  },
  {
    "app": "gnome-terminal",
    "title": "Terminal",
    "id": 23456789,
    "bounds": {"X": 100, "Y": 100, "Width": 800, "Height": 600},
    "area": 480000
  }
]

Get Active Window Info: Returns JSON with info about the currently focused window.

python3 capture-screen-linux/window_info.py active

2. Take Screenshots

Full Screen Screenshot

Run the python script with the full command:

python3 capture-screen-linux/screenshot.py full <output_path>

Example:

python3 capture-screen-linux/screenshot.py full /tmp/my_screen.png

Window Screenshot

Run the python script with the window command, specifying the application name or window title and output path.

⚠️ Important: Use the app name or title from window_info.py list output. The script supports fuzzy matching (searches in both app name and title).

python3 capture-screen-linux/screenshot.py window "<App Name or Title>" <output_path>

Examples:

python3 capture-screen-linux/screenshot.py window "Firefox" /tmp/firefox_window.png
python3 capture-screen-linux/screenshot.py window "gnome-terminal" /tmp/terminal_window.png
python3 capture-screen-linux/screenshot.py window "Code" /tmp/vscode_window.png

List Windows (Human Readable)

To see a formatted table of windows for quick reference:

python3 capture-screen-linux/screenshot.py list

Dependencies & Requirements

• Linux with X11 display server (most desktop environments)
• Python 3
• Required Python packages:
  • python-xlib - For X11 window management
• Required system tools (at least one):
  • scrot (recommended) - Simple screenshot tool
  • imagemagick (import command) - Advanced image manipulation
  • gnome-screenshot - GNOME desktop screenshot tool

Installation

Ubuntu/Debian

# Python dependencies
pip3 install python-xlib

# System screenshot tools (install at least one)
sudo apt-get install scrot imagemagick gnome-screenshot

Fedora/RHEL

# Python dependencies
pip3 install python-xlib

# System screenshot tools (install at least one)
sudo dnf install scrot ImageMagick gnome-screenshot

Arch Linux

# Python dependencies
pip3 install python-xlib

# System screenshot tools (install at least one)
sudo pacman -S scrot imagemagick gnome-screenshot

Technical Details

Window Identification

• Uses X11 protocol via python-xlib
• Queries _NET_WM_NAME for window titles
• Queries WM_CLASS property for application names
• Filters visible windows using IsViewable state
• Sorts by area to prioritize main windows

Screenshot Methods

• Full screen: Uses scrot, gnome-screenshot, or import (ImageMagick)
• Window capture: Uses import with window ID (most reliable method)
• Automatically detects available tools and uses the best option
• Outputs PNG format images

Display Server Support

• ✅ X11: Full support with window enumeration
• ⚠️ Wayland: Limited support
  • Full screen screenshots work with most tools
  • Window-specific capture may not work due to Wayland security restrictions
  • Consider using X11 compatibility mode (XWayland) for full functionality

Troubleshooting

"Cannot connect to X display" Error

This means you're not running under X11 or the DISPLAY variable is not set.

Solutions:

• Ensure you're running in a graphical environment
• Check if X11 is running: echo $DISPLAY (should show something like :0)
• If using SSH, enable X11 forwarding: ssh -X user@host

Import Errors

If you see ImportError: No module named 'Xlib':

pip3 install python-xlib

No Screenshot Tool Available

Install at least one screenshot tool:

# Recommended - lightweight and fast
sudo apt-get install scrot

# Alternative - more features
sudo apt-get install imagemagick

Wayland Compatibility

If you're running Wayland and experiencing issues:

1. Check your session type: echo $XDG_SESSION_TYPE
2. For window-specific captures, switch to X11 session at login
3. Or use XWayland compatibility:

   # Force app to run under XWayland
   GDK_BACKEND=x11 python3 capture-screen-linux/screenshot.py ...
   

Window Not Found

If a window isn't being captured:

1. Ensure the window is visible (not minimized)
2. Check the exact app name or title using the list command
3. Try using a partial match from the title
4. For flatpak/snap apps, the app name might be different (check with list)

Permission Issues

Some desktop environments may require additional permissions for screenshot tools:

• GNOME may show a permission dialog on first use
• Grant "Screenshot" permission in privacy settings if prompted