Grub: Grub is a type of boot loader used to boot into main OS.
Updating Grub Background
Step 1: Follow /boot/grub/themes/kali/ directory
Step 2: Open “theme.txt” with text editor. (with sudo permissions)
Step 3: Replace desktop-image: “background.png with your image name, and save file. (make sure to copy image in same /boot/grub/theme/kali/ before modifying “theme.txt” file)
Step 4: Run “update-grub” command with sudo permission.
Updating Grub Boot Menu time
Step 1: Traverse into /usr/share/grub/default
Step 2: Search for grub and open it with text editor. (with sudo permissions)
Step 3: Change “GRUB_TIMEOUT=5”. Numeric value represent how much seconds grub menu will display before loading default selection.