Ubuntu: legacy boot in case of lost uefi ubuntu



Question:

I have windows and ubuntu installed in uefi mode. But, if I loose my bios config or reset settings to default, I loose ubuntu's boot. And when it's happens, I just can boot windows. I think there is one win-uefi when applying defaults.

So, I have to take a pendrive, write a boot repair, reboot for repair, ... Can I have, some how, I way to solve it? I can change bios to boot uefi and legacy.


Solution:1

If both your OSes are booting in EFI mode, then there's no point in playing with the BIOS/CSM/legacy options in your firmware. Leave them disabled; enabling any such option is most likely to cause problems.

You shouldn't need to adjust your firmware settings on a regular basis, so this sort of problem should be something that crops up pretty rarely. If you are adjusting your firmware settings on a regular basis, that most likely indicates a problem of some type. If this is the case, I recommend you start a new question describing why you're making these regular adjustments and ask for a fix or workaround.

If you do change your firmware settings in such a way that the computer boots straight to Windows, there are at least two in-Windows solutions:

  • Open an Administrator Command Prompt window and type bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi in that window. (In some cases, grubx64.efi may be required, rather than shimx64.efi; but normally shimx64.efi is more likely to work.)
  • Use the third-party EasyUEFI tool to reset the boot order or add an entry for EFI\ubuntu\shimx64.efi (or possibly EFI\ubuntu\grubx64.efi).

Another option is to create a USB flash drive with my rEFInd boot manager on it. You should then be able to boot from the USB drive, and from there boot either Windows or Ubuntu. If you boot Ubuntu, you can restore GRUB by using efibootmgr, as described here or here. Note, however, that the prepared rEFInd USB image from the download site works only if Secure Boot is disabled. If your system has Secure Boot active, you'll need to either disable it or prepare your own USB image of rEFInd with Shim or PreLoader. (The ALT Linux image referenced on the rEFInd page might also work.)


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