I installed XUbuntu on a fast usb key on a new computer using UEFI mode. When I try to boot on this usb key with a old computer, it doesn't work.

After F12 and selected USB, the screen is black with an horizontal cursor is blinking. Obviously, the MBR is not set up or my bios doesn't support GPT tables. (laptop from 5years ago)

Where and how to check if my usb key is able to being booted on both ways ? In the case the MBR boot is unable, how to create it beside the UEFI mode ?

The CPU is an Intel Core2Duo T9900. The USB stick is a Sandisk Extreme 64GB. It's pretty weird because my windows 7 is a 64bits version and of course XUbuntu installed is the 64bits version.

  • Normally, it should work on both. That said, I have seen this behaviour when trying to launch the 64-bit version on a 32-bit machine. It might be a lead, but I guarantee nothing. What version is the USB stick and what is the CPU of that 5 year old machine? – jawtheshark Sep 15 '16 at 15:14
  • It's quite weird, windows 7 installed on the old machine is 64bits version and the XUbuntu installed too. – Alexis_FR_JP Sep 15 '16 at 15:21
  • Then it's not that. It was just something that could have been a source of error. (Which is why I chose to comment, and not put it as an answer) – jawtheshark Sep 15 '16 at 15:22
  • If this is a real installation of Xubuntu and installed in UEFI-mode, then the USB-key will not be bootable on older machines which doesn't support UEFI. You would have to install in legacy-mode (good old BIOS),but this would be a bit slow on USB2.0... – mook765 Sep 15 '16 at 15:46
  • It is in USB3.0, you should see the benchmark of this usb key, well enough to run without slowing down. The live usb can be bootable in both uefi and legacy-mode, would like to keep this feature on the installation. – Alexis_FR_JP Sep 16 '16 at 2:32

BIOS and EFI require entirely different boot loaders. (To be sure, GRUB2 is available for both environments, but those are different GRUB2 binaries -- sort of like Firefox being available for both Windows and Linux.) Thus, to boot on both BIOS and EFI computers, a medium needs to include both BIOS and EFI boot loaders. You've already got an EFI-mode version of GRUB2 installed, so that means you must install a BIOS-mode boot loader. I recommend avoiding GRUB2 for this, simply to avoid the possibility of conflicting or confusing GRUB2 configuration files. That said, it is possible to get both BIOS-mode and EFI-mode GRUB2 installations to coexist; I simply don't know the details of any "gotchas." You might want to look into SYSLINUX for this task, but I'm afraid I can't provide step-by-step installation instructions.

  • I prefer just to create separate BIOS or UEFI boot drives. But Ubuntu live installer is configured for both. I do use gpt and include both the ESP - efi system partition and bios_grub so I can convert from one to the other. But some have created both: Flash drive to boot in UEFI or BIOS - sudodus help.ubuntu.com/community/Installation/UEFI-and-BIOS and: A new and so far successful attempt to create a stable portable system, that works in UEFI and BIOS mode ubuntuforums.org/… – oldfred Sep 15 '16 at 21:54
  • Yes, the live-usb can be bootable for both. It should be possible then. I don't want to choose bios because I'd like to boot on my UEFI-only tablet. I'll try the final link. Seems very good and exactly what I'm looking for. Thank you ! – Alexis_FR_JP Sep 16 '16 at 2:37

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