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

[udippel]

I was looking around and found this:

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3,8G     0  3,8G   0% /dev
tmpfs           786M  3,5M  783M   1% /run
/dev/sda8        28G   18G  9,0G  66% /
tmpfs           3,9G  277M  3,6G   8% /dev/shm
tmpfs           5,0M  4,0K  5,0M   1% /run/lock
tmpfs           3,9G     0  3,9G   0% /sys/fs/cgroup
/dev/loop1       56M   56M     0 100% /snap/core18/1885
/dev/loop0      240M  240M     0 100% /snap/chromium/1328
/dev/loop3       31M   31M     0 100% /snap/snapd/9279
/dev/loop2       63M   63M     0 100% /snap/gtk-common-themes/1506
/dev/sda6       453M  173M  253M  41% /boot
/dev/sda9        93G   73G   16G  83% /home
/dev/sda2       993M   33M  960M   4% /boot/efi
tmpfs           786M   20K  786M   1% /run/user/1000

Maybe; but I wouldn't be too sure that it was like that before, with the
/boot/efi.

It was strange though, that after having added *buntu to W10 some two years ago, though without a hitch, I had found two W10 boot partitions in grub, I think sda2 and sda3. Both had booted properly, whichever I selected. Never understood that; and never really bothered. 
Maybe, only maybe, this helps explaining the misbehaviour encountered at upgrade?
Btw. sda3 is now fat32, with the label SYSTEM_DRV.

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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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