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Brad Thompson avatar Ubuntu

Grub does not detect Windows in dual boot

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Brad Thompson

Ubuntu 20.04.3
Dual boot

Hi everyone,

I have a dual boot Ubuntu/Windows and used to select OS from a text grub menu. After the last Windows update a few days ago I think the boot was overwritten and I could boot only Windows.

I tried to restore grub from live media (boot in Legacy mode only) but installing grub on EFI partition was not allowed. It was possible only after I created a new 1M BIOS boot partition (sda10) with a bios_grub flag. Now I can boot Ubuntu but only when I changed from BIOS settings to CSM from UEFI (when UEFI has enabled only Windows boots).

UEFI was not booting Ubuntu but Windows only. Live media boot only in a Legacy mode, not UEFI. The only option was to change to Legacy.

os-prober does not see the Windows. https://help.ubuntu.com/community/UEFI I tried boot-repair but ends up with an error. Later the source of error was removed.

Since yesterday I repaired with boot-repair.

I pasted below some relevant info let me know please if you need anything else. Thank you.

fstab:

# / was on /dev/sda6 during installation
UUID=6c04f6aa-3801-4066-8acf-36b4500287c0 /               ext4    errors=remount-ro 0       1
# /boot/efi was on /dev/sda2 during installation
UUID=2CD1-0B3E  /boot/efi       vfat    umask=0077      0       1

[ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"

Legacy boot on HDD

cfdisk:

                                               Disk: /dev/sda
                                        Size: 698.65 GiB, 750156374016 bytes, 1465149168 sectors
                                      Label: gpt, identifier: 3882C4AF-416A-43E7-A057-D27E36BD07AC

    Device                            Start                 End            Sectors            Size Type
    /dev/sda1                          2048              923647             921600            450M Windows recovery environment
>>  /dev/sda2                        923648             1128447             204800            100M EFI System                           
    /dev/sda3                       1128448             1161215              32768             16M Microsoft reserved
    /dev/sda4                       1161216           396725504          395564289          188.6G Microsoft basic data
    /dev/sda5                     396726272           406966271           10240000            4.9G Microsoft basic data
    /dev/sda6                     406966272           408893439            1927168            941M Windows recovery environment
    /dev/sda7                     408893440           805044223          396150784          188.9G Linux filesystem
    /dev/sda8                     805044224          1463195647          658151424          313.9G Linux filesystem
    /dev/sda9                    1463195648          1465145343            1949696            952M Linux swap
    /dev/sda10                   1465145344          1465147391               2048              1M BIOS boot


 ┌────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
 │ Partition name: EFI system partition                                                                                               │
 │ Partition UUID: FC73FEE6-9F08-447A-9278-0B4265841314                                                                               │
 │ Partition type: EFI System (C12A7328-F81F-11D2-BA4B-00A0C93EC93B)                                                                  │
 │Filesystem UUID: 2CD1-0B3E                                                                                                          │
 │     Filesystem: vfat                                                                                                               │
 │     Mountpoint: /boot/efi (mounted)
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ChanganAuto avatar
us flag
ChanganAuto
All you'd need to do was UEFI > Boot and change it back to "Ubuntu". Windows feature updates tend to change the boot order to Windows due to the many reboot they need until finished. But instead you basically changed a proper UEFI installation into a Legacy one. Knowing that Windows wasn't changed (and it shouldn't) the "Legacy" Grub CAN'T detect it now.
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mchid avatar
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mchid
Ubuntu won't see windows if windows is in fastboot mode. Did you disable fastboot from your windows settings?
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ChanganAuto avatar
us flag
ChanganAuto
@mchid It could be it but it's something more mundane: Lack of understanding about basic UEFI stuff. Instead of changing the boot order back to Ubuntu after the Windows feature update, the OP transformed a perfectly fine UEFI mode Ubuntu into Legacy, that's all.
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Brad Thompson avatar
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Brad Thompson
@ChaganAuto glad some understand very well, UEFI was not booting Ubuntu but Windows only. Live media boot only in a Legacy mode, not UEFI. The only option was to change to Legacy. What would you do basically ?
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karel avatar
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karel
Booting both Ubuntu and Windows in UEFI mode looks promising. You can convert Ubuntu from BIOS mode to UEFI mode by following the instructions in [this answer](https://askubuntu.com/a/981415/). Also in the same answer are instructions for converting Ubuntu back to BIOS mode from UEFI mode in case it doesn't work. Please comment to me @karel about the results.
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Brad Thompson avatar
nl flag
Brad Thompson
@mchid yes, fastboot mode was disabled. I enabled just for testing and I can see windows with fastbooting enabled.
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Brad Thompson avatar
nl flag
Brad Thompson
@karel that is what I did yesterday with boot-repair but failed a few times. Then after a few tweaks, successfully installed grub-efi and I was able to dual boot. Thanks!
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karel avatar
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karel
Does this answer your question? [In a dual boot system, how does the BIOS choose which bootloader to run?](https://askubuntu.com/questions/981382/in-a-dual-boot-system-how-does-the-bios-choose-which-bootloader-to-run) and [Why 12.04 Fails to install grub-efi to /target/?](https://askubuntu.com/q/260297/)
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