I have just installed Debian 10 (Buster). I have come to the conclusion that UEFI does not work on my device (despite it being in the firmware setup). For some reason, the install has converted the old MBR/DOS partition table into GPT. And now it dose not boot.

I would like to ether convert it back. Or keep GPT, but convert boot loader to use old method, maybe using protective MBR https://en.wikipedia.org/wiki/GUID_Partition_Table#Hybrid_MBR_(LBA_0_+_GPT) . I have tried to re-install grub using the installer rescue mode, but this fails ( see new Debian install will not boot if you want more detail on this ).

So how do I make it bootable using MBR, without reinstalling whole OS (and /home)?

I am booted into gparted live.

fdisk -l /dev/sda shows

  • Partition table type (Disklabel type): gpt
  • root partition type: EFI System
  • 4 blocks free at end of disk (for 2nd copy of gpt)

fdisk -t mbr -l /dev/sda shows

  • The whole disk reserved for GPT (protective MBR)
  • If you're currently in GPT but using BIOS, you have to create an extra bios_grub partition(might need to be the first partition) because GPT doesn't allow enough space to embed the grub stage 1.5. Then use nornal grub-install as in normal BIOS mode. Or find someway to convert GPT back to MBR, but if you have more than 4 partition under GPT, it would be hard, since partition header already occupied by filesystem so can't support EBR. In that case, you'll have to move the whole filesystem. Not impossible, but very tedious. – 炸鱼薯条德里克 Aug 11 '19 at 12:26
  • Out of curiosity, why do you think that your device's UEFI firmware will not boot Debian 10? What is the make/model of your device? – fpmurphy Aug 11 '19 at 12:30
  • It is a lenovo yoga 3 11. When I tell it to boot the installer USB via UEFI, it does boot, but then I can't get it to work (can't remember the errors). When I ask it to boot the main disk via UEFI, it shows a white flashing underscore in the top left of a black screen. – ctrl-alt-delor Aug 11 '19 at 12:35
  • @炸鱼薯条德里克 I have 1M “Un-used” at start of disk (a few blocks for the gpt, then I don't know what), is it possible to use this space. How can I find out what it is? – ctrl-alt-delor Aug 11 '19 at 12:38
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    "arbitrary", spelling error. When you install grub, you specify a boot-directory, then grub-install will install proper module into stage1.5 so it will have ability to read from stage2, which is bunch of files in the filesystem – 炸鱼薯条德里克 Aug 12 '19 at 22:37

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