I was upgrading my Ubuntu and the upgrade stopped with the following message.
The GRUB boot loader was previously installed to a disk that is no longer present, or whose unique identifier has changed for some reason. It is important to make sure that the installed GRUB core image stays in sync with GRUB modules and grub.cfg. Please check.
I have no idea how to check this. This computer was given to me by my sister.
I encountered that message on a desktop PC that I had booted with an Ubuntu installation on a USB drive. The PC's internal SSD contained a Windows installation. I didn't want to mess up the Windows drive.
To deal with this, I hit OK to move on from that initial GRUB window to a list of devices where GRUB could be installed.
At that point, I ran lsblk in a separate window. It made clear that, aside from various loop devices, my drives were /dev/sda and /dev/nvme0n1. I knew the NVMe drive was my internal SSD because I bought and inserted an NVMe drive in that desktop PC. So the USB drive was /dev/sda. I could have further verified this by running GParted or Disks and looking for telltale signs (e.g., drive size).
Aside from the NVMe drive, the GRUB window was still offering two choices: /dev/sda or /dev/sda3. I installed only to /dev/sda, because I wanted GRUB on the drive, not on a partition within the drive. To do that, I used my arrow key to move down to the /dev/sda item, and then hit the spacebar to select it. Then I hit Tab to highlight OK, and hit Enter.
This GRUB issue came up when I was trying to update the USB drive's Ubuntu installation. After I selected /dev/sda, that update process continued, and it presented me with another GRUB choice. This time, it was a choice between /dev/nvme0n1p2 and /dev/sda2. As before, I didn't want to install to a partition (in this case, sda2). I wanted to install only to the whole drive (/dev/sda). So in this case I unselected both options. That led to a window telling me,
Configuring grub-efi-amd64-signed.
You chose not to install GRUB to any device.
That was true for this particular query, but not for the updating process as a whole. I had already designated /dev/sda previously. So I went ahead with nothing selected. When the update process was done, I rebooted the Ubuntu USB drive. It booted successfully.
Use Space to switch between options (it should be /dev/sda). Then press Enter.
