I had a dual-boot EFI-based Windows/Linux system, with grub2 pointing to an Ubuntu 18.04 /root partition in /dev/sda6.

I tried installing Ubuntu 20.04 in /dev/sda5, which was a spare partition. This install went okay, but hung on the grub-install phase. After that, grub no longer works. I just get a grub> prompt. I can escape out to the boot manager and boot Windows, but grub is hosed.

So, I booted the live Ubuntu 18.04 flash drive and attempted to rerun grub-install for the original 18.04 system in /dev/sda6 by mounting /dev/sda6 on /mnt and running

sudo grub-install --boot-directory=/mnt/boot /dev/sda

That resulted in this message

Installing for i386-pc platform.
grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub-install: warning: Embedding is not possible.  GRUB can only be installed in this setup by using blocklists.  However, blocklists are UNRELIABLE and their use is discouraged..
grub-install: error: will not proceed with blocklists.

Is there any way to fix this. It looks like something has messed up my partition table (or something), but the partitions themselves are okay. I can mount them and examine them under the live USB. I specifically asked UBU 20.04 to install grub in the partition device (/dev/sda5) rather than on the disk device (/dev/sda). Was that wrong?

I suppose, as long as /home is preserved (it's in /dev/sda8), I'm okay with something that wipes out my old 18.04 /root...

1 Answer 1


I fixed it by reinstalling ubuntu 20.04 and letting it put a new grub loader into /dev/sda. The 20.04 grub installer detected my 18.04 system, so now I can boot either one.

Interestingly (?), the second install also appeared to hang for a long time during the update-grub phase (same as the first install did). But when I went to power the box down to get out of it, I didn't hold down the power button. The single press of the power button triggered a clean shutdown of the installer - rather than a forced one. Maybe that difference is why grub now works - I don't know.

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