os-prober and update-grub find windows install, yet it does not show in boot menu

My system runs Ubuntu 21.04. I recently moved the system from an old SSD to a new M.2 drive, using Clonezilla. In that process, I needed to run update-grub. The system boots up fine, but I cannot choose to boot the Windows 10 install I have on another drive, it is not in the grub menu when booting.

os-prober and update-grub both seem to find it no problem:
root@zap:/# os-prober
/dev/sdb1@/efi/Microsoft/Boot/bootmgfw.efi:Windows Boot Manager:Windows:efi
root@zap:/#
root@zap:/#
root@zap:/# update-grub
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.11.0-38-generic
Found initrd image: /boot/initrd.img-5.11.0-38-generic
Found linux image: /boot/vmlinuz-5.11.0-37-generic
Found initrd image: /boot/initrd.img-5.11.0-37-generic
Found linux image: /boot/vmlinuz-4.13.0-37-generic
Found initrd image: /boot/initrd.img-4.13.0-37-generic
Found linux image: /boot/vmlinuz-4.13.0-36-generic
Found initrd image: /boot/initrd.img-4.13.0-36-generic
Found Windows Boot Manager on /dev/sdb1@/efi/Microsoft/Boot/bootmgfw.efi
Adding boot menu entry for UEFI Firmware Settings
done
root@zap:/# 

What have I forgotten?

1 Answer

TL'DR:

sudo echo GRUB_DISABLE_OS_PROBER=false >> /etc/default/grub && sudo update-grub

Details:

OS Prober no longer ran by default in latest grub:

Warning: os-prober will not be executed to detect other bootable partitions. Systems on them will not be added to the GRUB boot configuration. Check GRUB_DISABLE_OS_PROBER documentation entry

Such kind of questions starts to show up since May 2021.

So I've followed the advice:

% sudo echo GRUB_DISABLE_OS_PROBER=false >> /etc/default/grub && sudo update-grub
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Sourcing file `/etc/default/grub.d/lubuntu-grub-theme.cfg'
Generating grub configuration file ...
Found theme: /usr/share/grub/themes/lubuntu-grub-theme/theme.txt
Found linux image: /boot/vmlinuz-5.13.0-19-generic
Found initrd image: /boot/initrd.img-5.13.0-19-generic
Found Windows Boot Manager on /dev/nvme0n1p1@/EFI/Microsoft/Boot/bootmgfw.efi
Found Ubuntu 20.04 LTS (20.04) on /dev/nvme0n1p6
Adding boot menu entry for UEFI Firmware Settings
done
$ tail -1 /etc/default/grub
GRUB_DISABLE_OS_PROBER=false
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 21.10
Release: 21.10
Codename: impish
$ os-prober
/dev/nvme0n1p1@/EFI/Microsoft/Boot/bootmgfw.efi:Windows Boot Manager:Windows:efi
/dev/nvme0n1p6:Ubuntu 20.04 LTS (20.04):Ubuntu:linux
grep menuentry /boot/grub/grub.cfg

Now I can see my Ubuntu 20.04 LTS boot entries in my /boot/grub/grub.cfg file, as well as Windows boot entry:

$ grep 'menuentry.*Windows' /boot/grub/grub.cfg
menuentry 'Windows Boot Manager (on /dev/nvme0n1p1)' --class windows --class os $menuentry_id_option 'osprober-efi-C633-8883' {

HTH