lockPicker

GDM Wallpaper Changer - Changes your Kali Screenlock Background

lockPicker - v1.0.0

Release Date: 28 Jan 2026 A simple, interactive Bash script to change your Kali Linux GDM login background easily with a GUI and safe image conversion.

Features

1. GUI-based Wallpaper Selection

Select wallpapers from any directory using a user-friendly dialog menu.

2. Live Preview

Preview the selected wallpaper before applying using feh, scaled to a 640x360 window for convenience.

3. Automatic Screen Resolution Detection

Detects your current screen resolution via xrandr and resizes wallpapers automatically to fit perfectly.

4. Safe Image Conversion

Converts wallpapers to a safe JPEG format using ImageMagick with optimized settings:

- resize to your screen resolution

- gravity center and -extent for perfect cropping

- strip, -interlace none, -sampling-factor 4:4:4, -quality 90 for safe GRUB/GDM use

5. Backup Functionality

Optionally backup the existing login-blurred background before applying changes.

6. Automatic GDM Update

Apply the new wallpaper and optionally restart GDM immediately to see changes.

7. Dynamic Temporary File Handling

Each conversion generates a unique temporary file to avoid overwriting previous runs.

Installation & Usage

Make sure dependencies are installed:

sudo apt install dialog feh x11-xserver-utils imagemagick

Run the script as root:

sudo ./lockPicker.sh

Follow the on-screen prompts to select and apply your wallpaper.

Notes

• Works on Kali Linux GNOME.
• Converted images are temporarily stored in /tmp with unique filenames to avoid conflicts.
• If ImageMagick fails to convert, ensure it is installed and functioning correctly.