Re: Advise on how to debug screen with only GRUB and blinking cursor and possibly save my dualboot installation

[Pascal Hambourg]

On 18/12/2022 at 20:49, Sophoklis Goumas wrote:
> I got to seeing simply a black screen only display GRUB and a blinking
> cursor as is also shown here:
> https://i.stack.imgur.com/4zJNc.jpg

"GRUB" alone means that the GRUB boot image was loaded but could not 
load the GRUB core image (it would have printed "loading" after "GRUB").

> My system is non-(U)EFI and it has two operating systems each on
> "its own" disk, namely:
> a debian GNU/Linux installation on a GPT partitioned disk (/dev/sda) and
> a Windows 10 on a installation on a MBR (MSDOS) disk (/dev/sdb).

> # parted /dev/sda print
> Model: ATA WDC WD1003FZEX-0 (scsi)
> Disk /dev/sda: 1000GB
> Sector size (logical/physical): 512B/4096B
> Partition Table: gpt
> Disk Flags:
>
> Number  Start   End     Size    File system     Name  Flags
>   1      1049kB  2149MB  2147MB  ext4                  bios_grub
>   2      2149MB  19.3GB  17.2GB  linux-swap(v1)        swap
>   3      19.3GB  1000GB  981GB                         lvm

This is wrong. A BIOS boot partition (bios_grub flag) should not contain 
a filesystem. The purpose of this type of partition is exclusively to 
store a raw GRUB core image.

In the rest of the data it appears that /dev/sda1 (hd0,gpt1) is used as 
/boot. Running grub-install installed the core image in the first 103 
sectors of /dev/sda1 and probably ruined the ext4 filesystem beyond repair.

If /dev/sda1 can be repaired and mounted without data loss:
- Reduce sda1 by 1MB and change its type to "Linux filesystem".
- Create a new 1 MB BIOS boot partition in the free space.
- Reinstall GRUB

If /dev/sda1 cannot be repaired and mounted any more:
- Reduce sda1 to 1MB.
- Create a new ext4 partition in the free space.
- Mount the new partition as /boot. Update /etc/fstab.
- Reinstall the kernel images and initramfs and GRUB