[Bug 1898022] Re: grub upgrade 18.04->20.04 loses dual-boot to W10

[udippel]

I made some progress:

$ grub-probe -t device /boot/grub
/dev/sda6

$ mount
[...]
/dev/sda6 on /boot type ext4 (rw,relatime)
/dev/sda2 on /boot/efi type vfat (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)

$ sudo ls /boot/efi/EFI/Ubuntu
BOOTX64.CSV  grub.cfg  grubx64.efi  mmx64.efi  shimx64.efi

$ dd if=/dev/sda bs=512 count=1 2> /dev/null | grep -q GRUB && echo "GRUB found"
$

If I read these correctly, I do have files, but since the update no more
MBR in /dev/sda. Is this observed correctly?

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https://bugs.launchpad.net/bugs/1898022

Title:
  grub upgrade 18.04->20.04 loses dual-boot to W10

Status in grub2 package in Ubuntu:
  New

Bug description:
  (Summary says it:)

  Upgraded by dual-boot kubuntu 18.04 to kubuntu 20.04. After the restart, dual-boot was gone, and it boots directly into kubuntu. 
  I guess it is a problem with grub, because the boot menu doesn't show. However, the 'lenovo' shows trice, while it used to show once with 18.04; followed by the grub boot menu. 

  I guess that the MBR was written into haywire?

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: grub-efi-amd64-bin 2.04-1ubuntu26.4
  ProcVersionSignature: Ubuntu 5.4.0-48.52-generic 5.4.60
  Uname: Linux 5.4.0-48-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27.9
  Architecture: amd64
  CasperMD5CheckResult: skip
  CurrentDesktop: KDE
  Date: Thu Oct  1 11:34:39 2020
  InstallationDate: Installed on 2019-03-14 (566 days ago)
  InstallationMedia: Kubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
  SourcePackage: grub2
  UpgradeStatus: Upgraded to focal on 2020-09-29 (1 days ago)

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