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I want to be able to boot from HD normally but also boot from USB if something gets broken in my dual-boot setup. It should be transparent to the OSes. Are there any issues with this?

Luke P
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1 Answers1

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  • If you can unplug or disconnect the internal drive, it is rather easy to install Ubuntu (or I would prefer the ultra light-weight Lubuntu) into a USB pendrive.

  • When you have that system, and know that it works, you can turn off the computer and plug in the internal drive again.

  • Boot into the system installed in the USB drive and run the following command

    sudo update-grub

    This way, the system should find the operating system(s) in the internal drive and create menu entries for them in the grub menu (of the system in the external drive).

  • Test that it really works by rebooting and selecting a menu entry for a system in the internal drive.

  • If you are booting in UEFI mode and dual boot with Windows: Please avoid booting Windows from the internal drive, while the USB drive with your new system is connected. It might destroy the USB drive's boot system.

sudodus
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  • Sounds good...I may do that. I still have the question: If I did an install of GRUB to USB from my active Ubuntu, will it supersede or bypass my current boot loader? In other words would the USB be my only means of booting? – Luke P Jan 20 '19 at 20:36
  • If you install grub to USB drive with Ubuntu (or Lubuntu), you will not install anything in your internal drive. So it is safe to do that, but be very careful (check and double-check, that you are pointing to the corrent device and file system). In UEFI mode, the system will write to the internal drive -- this is why I suggest to unplug the internal drive. -- You can do the whole thing the manual way and get a very light-weight grub system in your USB drive (but I think it is easier to have an installed system there, so that you can use the standard tools like sudo update-grub). – sudodus Jan 20 '19 at 20:50