To set a wallpaper in i3, you can use a program called feh. Here’s how you can do it:

  1. Install feh if it’s not already installed. You can do this by running the following command: 
    sudo apt-get install feh

  2. Choose the image you want to set as your wallpaper and remember its file path.

  3. Open your i3 configuration file using a text editor. The default location for the configuration file is ~/.config/i3/config.

  4. Add the following line to your i3 configuration file, replacing <file_path> with the actual path to your image file: 
    exec --no-startup-id feh --bg-fill <file_path>

  5. Save the changes to your i3 configuration file and exit the text editor.

  6. Restart i3 for the changes to take effect. You can do this by pressing Mod+Shift+R (by default, Mod refers to the Super or Windows key).

After restarting i3, your chosen image should be set as the wallpaper.