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I have three OS installed on my PC: Windows 10 and Ubuntu 18.04 on a HDD, and an Ubuntu 20.04 on a SSD. The bootloader is on the HDD.

After a typical update from 18.04, the GRUB was rewritten, and now I only have access to those OSs that are installed on the HDD.

I would like to rescue that GRUB install from Ubuntu 20.04, so I can restore access to all OSs, so I wonder which is the best procedure to do that. I apologize in advance if this is a solved question, but any hint in that respect would be nice.

I provide my fdisk -l results for more information. Thanks!

Disk /dev/sda: 931,5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: C4EF944E-5B36-4774-9395-BA8922E84757

Device          Start        End   Sectors   Size Type
/dev/sda1        2048     534527    532480   260M EFI System
/dev/sda2      534528     567295     32768    16M Microsoft reserved
/dev/sda3      567296  996851711 996284416 475,1G Microsoft basic data
/dev/sda4  1918451712 1920458751   2007040   980M Windows recovery environment
/dev/sda5  1920458752 1953511423  33052672  15,8G Microsoft basic data
/dev/sda6   996851712 1012852735  16001024   7,6G Linux swap
/dev/sda7  1012852736 1918451711 905598976 431,8G Linux filesystem

Disk /dev/nvme0n1: 477 GiB, 512110190592 bytes, 1000215216 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Gustavo Espínola Mena
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  • Have you tried `boot-repair`? (It has to be run from a live session) – Nmath Sep 10 '20 at 21:32
  • Oh, not yet, I have in fact tested tutorials with boot-repair, which did not work, but I have not tried live session yet. I will try that in a moment. – Gustavo Espínola Mena Sep 10 '20 at 22:02
  • Did not work, I provide the following pastebin: https://paste.ubuntu.com/p/CKs8SrC9VY/ – Gustavo Espínola Mena Sep 10 '20 at 22:30
  • Hmmm.. on the section headed "OS detected" it seems to have only caught/fixed the two that are installed on `sda`, but it does also show 20.04 on the nvme. Are all three installed using either UEFI or BIOS/legacy? They should all be the same. And if they are UEFI, you need to keep all OS drives connected during installation (otherwise maybe you have a duplicate EFI on the nvme). You should only have one EFI partition for the whole device – Nmath Sep 10 '20 at 22:57
  • Uh oh, I do not fully understand yet the exact difference between UEFI or BIOS install. However, I do remember that, when I was installing Ubuntu 20.04 on my SSD, I have chosen to format the entire SSD as ext4 and mount as /, as well as /dev/sda bor boot loader installation. That seemed to work just fine as I was able to choose between 18.04, 20.04 and W10 on boot, but after this 18.04 update, I can't do that anymore (only 18.04 or W10). Should I have chosen the /dev/sda1 instead? The EFI System partition that is in the HDD? – Gustavo Espínola Mena Sep 10 '20 at 23:48
  • gdisk on /dev/nvme0n1 returns: Partition table scan: MBR: not present BSD: not present APM: not present GPT: not present – Gustavo Espínola Mena Sep 10 '20 at 23:50
  • It sounds like you did the right thing with the bootloader installation at `sda`. However something seems fishy about the nvme not being able to find a MBR or GPT partition scheme. Are you able to use your file manager to mount this drive and navigate the file system? MBR/BIOS/Compatibility are all associated together and are the "old way" of partitioning/booting volumes. Newer hardware uses GPT/UEFI for the same purpose. The most important thing for dual boot is that you're consistently using one or the other. Sorry at this point I can't think of much else to review. Puzzling.. – Nmath Sep 11 '20 at 00:16
  • Thanks for your answers! I'll still try to figure it out, one way or another. The file manager at 18.04 is able to mount the SSD, so I can recover any file I need, just in case I cannot find any other solution. – Gustavo Espínola Mena Sep 11 '20 at 00:30
  • I've seen a few posts which recommend enabling/disabling certain BIOS settings in order for nvme drives to be recognized correctly. https://askubuntu.com/questions/1271871/nvme-ssd-is-not-detected-by-the-ubuntu-20-04-installer | https://askubuntu.com/questions/696999/unable-to-install-grub-in-dev-nvme - worth a try to further investigate your BIOS settings – Nmath Sep 11 '20 at 02:26
  • You need to turn Windows fast start up off. Have you updated UEFI and SSD firmware. Are drives still in AHCI mode. Windows updates may reset UEFI and turn fast start up back on. It sounds like you installed 20.04 in BIOS/MBR mode, not UEFI/gpt mode. How you boot install media, is how it installs. Shows live installer with screen shots. Both BIOS purple accessibility screen & UEFI black grub menu screen https://help.ubuntu.com/community/UEFI May need to change drive to gpt (that will erase it) and reinstall in UEFI mode. Do not leave as MBR. – oldfred Sep 11 '20 at 03:45

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