Linux – switch to Legacy Boot from EFI on Debian Linux

bootlinuxuefi

My motherboard died for an AMD Phenom processor, so I ordered a cheap replacement on ebay. It works, but it's old.

I connected my hard drive (it shows a /boot/efi partition in /etc/fstab) to the new motherboard and the bios didn't see the boot. I connected an old hard drive (it does not show a /boot/efi partition in /etc/fstab) to the motherboard, and the bios did see that boot.

There is no option for UEFI in the bios. It's an MSI board with something called 2.2 Tb Infinity on the boot menu, which supposedly is something like UEFI (according to Google), but then again, it's not.

I can now boot both hard drives, because I updated grub from the old hard drive and it found my EFI boot (not sure how that works). But it's a Frankenstein system, and the old hard drive is showing signs of failure.

Is there any way for me to switch my EFI boot to a legacy boot so I don't have to go through another disk to boot? I have all my data saved and could reinstall, but there's a lot of configuration of my system that I don't want to lose or have to redo.

I apologize if I've misdescribed the problem. I'm not a newbie, but I'm not a programmer either. Some things are just a black box to me. Thanks beforehand.

Best Answer

This is for Installation without encrytion. You have to know how you can chroot! The most must be done as root or with sudo.

Download a Live-Linux with the same arch (32-bit or 64-bit)like your
Debian-installation. You can also use your older harddrive and boot from

USB with it, if you have a chase or adapter for it. The arch mußt be the same too.
You has later to chroot in your Debian, because we have to install same packages.
comment the entry for /boot/efi in /etc/fstab out.
mount this efi-partition temporary and cp the content from /boot/ folder to the /boot folder in the /-Partiton.
Now we have to create a special partition. Umount every partition from

your debian-harddrive. Easiest way start gparted. Search for your /boot/efi partition and erase it, create a new one (min. size 4MB)
- Mount point: none
- Type: no filesystem
- Flag: bios_grub

It will be used as raw-device. better english and more information

Control after leaving gparted with parted -l That your new partition have the same output

Number Start End Size File system Name Flags 4 17.4kB 1049kB 1031kB BIOS boot partition bios_grub

Besides Nr. and size. Name and flag is important.

Now you have to chroot in your debian. you need acess to internet too in chroot.
apt update && apt-get install --reinstall linux-image-$(uname -r) linux-headers-$(uname -r) this is for security.
apt install grub-pc This will deinstall the most grub-efi packages.
grub-install /dev/sdx x is a placeholder for the debian-harddrive. you can repeat the configuration from grub-pc with dpkg-reconfigure grub-pc if something went wrong.
check with fdisk -l 2>/dev/null | egrep "Disk /|/dev/" | sed "s#^/dev/#Part /dev/#" | awk '{print $2}' | sed 's/://' | xargs -n1 -IX sudo sh -c "hexdump -v -s 0x80 -n 2 -e '2/1 \"%x\" \"\\n\"' X | xargs -n1 -IY sh -c \"case \"Y\" in '48b4') echo X: GRUB 2 v1.96 ;; 'aa75' | '5272') echo X: GRUB Legacy ;; '7c3c') echo X: GRUB 2 v1.97 oder v1.98 ;; '020') echo X: GRUB 2 v1.99 ;; *) echo X: Kein GRUB Y ;; esac\"" Grub is in the MBR from your debian-hard-drive.
grub-mkconfig and update-grub
Last check compare the output from blkid with entries in /etc/fstab

No errors? Then start debian.

B.t.w. what is a Frankenstein system?

Forgotten one cmd . update-initramfs -u -k all

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Looking at the drive with gdisk renders:

root@ubuntu-mate:~# gdisk /dev/sda
GPT fdisk (gdisk) version 1.0.1

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): v

Warning: The 0xEE protective partition in the MBR is marked as active. This is
technically a violation of the GPT specification, and can cause some EFIs to
ignore the disk, but it is required to boot from a GPT disk on some BIOS-based
computers. You can clear this flag by creating a fresh protective MBR using
the 'n' option on the experts' menu.

No problems found. 2925 free sectors (1.4 MiB) available in 2
segments, the largest of which is 2014 (1007.0 KiB) in size.

Following the instructions from gdisk:

Command (? for help): ?   
b   back up GPT data to a file
c   change a partition's name
d   delete a partition
i   show detailed information on a partition
l   list known partition types
n   add a new partition
o   create a new empty GUID partition table (GPT)
p   print the partition table
q   quit without saving changes
r   recovery and transformation options (experts only)
s   sort partitions
t   change a partition's type code
v   verify disk
w   write table to disk and exit
x   extra functionality (experts only)
?   print this menu

Command (? for help): r

Recovery/transformation command (? for help): ?
b   use backup GPT header (rebuilding main)
c   load backup partition table from disk (rebuilding main)
d   use main GPT header (rebuilding backup)
e   load main partition table from disk (rebuilding backup)
f   load MBR and build fresh GPT from it
g   convert GPT into MBR and exit
h   make hybrid MBR
i   show detailed information on a partition
l   load partition data from a backup file
m   return to main menu
o   print protective MBR data
p   print the partition table
q   quit without saving changes
t   transform BSD disklabel partition
v   verify disk
w   write table to disk and exit
x   extra functionality (experts only)
?   print this menu

Recovery/transformation command (? for help): x

Expert command (? for help): ?
a   set attributes
c   change partition GUID
d   display the sector alignment value
e   relocate backup data structures to the end of the disk
g   change disk GUID
h   recompute CHS values in protective/hybrid MBR
i   show detailed information on a partition
l   set the sector alignment value
m   return to main menu
n   create a new protective MBR
o   print protective MBR data
p   print the partition table
q   quit without saving changes
r   recovery and transformation options (experts only)
s   resize partition table
t   transpose two partition table entries
u   replicate partition table on new device
v   verify disk
w   write table to disk and exit
z   zap (destroy) GPT data structures and exit
?   print this menu

Expert command (? for help): n

Expert command (? for help): w

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!

Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/sda.
Warning: The kernel is still using the old partition table.
The new table will be used at the next reboot or after you
run partprobe(8) or kpartx(8)
The operation has completed successfully.

Reboot and I'm greeted by rEFInd again! Qubes won't boot any more of course.

Seems the protective mbr created by Qubes was the problem.

Best Answer

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