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Boot Image & GRUB

⚠️ GRUB and Boot Splash Considerations in Custom Ubuntu ISOs

When building a custom Ubuntu-based ISO using Cubic, one of the legal and technical considerations involves the boot splash image and GRUB configuration. Ubuntu’s default boot process includes branding (Lubuntu/Ubuntu logos) that you cannot redistribute without permission. Understanding how this works and how to handle it is essential.

1️⃣ Live Boot vs Installed System

  • Live Boot:

  • When the ISO is booted directly from media (USB/DVD), the GRUB loader shows the initial boot menu.

  • The first screen often includes the Ubuntu or Lubuntu splash screen.

  • Editing Plymouth themes inside the Cubic environment does not affect the live boot splash. The live system is still using the original Ubuntu branding.

  • Installed System:

  • Once the ISO is installed to disk, the changes you made in Plymouth and custom themes will apply.

  • The installed system can display your custom splash screen and branding.

Key Takeaway: The first boot from live media will always show the default splash unless you intervene at the GRUB level.

To avoid displaying Ubuntu branding during first boot, modify the GRUB configuration after exiting the Cubic virtual environment:

  1. Open the GRUB configuration file in your custom-root:
custom-root/boot/grub/grub.cfg
  1. Locate the kernel boot line that looks like this:
linux /vmlinuz ... quiet splash
  1. Remove the --quiet splash options, leaving:
linux /vmlinuz ...

Effect:

  • Disables the Ubuntu splash screen during live boot.
  • Prevents legal issues related to redistribution of Ubuntu’s branding.
  • The system still boots normally, showing only textual output until installation.