Comment 0 for bug 1840697

Issue seen on Ubuntu 19.04 (workstation); might present in previous versions ?

Previous situation ("pre-bug") :

/dev/sda = WDC disk 2TB
/dev/sdb = SSD disk, 256GB
boot loader in /dev/sda

Ubuntu 19.04 wks installed before Windows

disk layout:
  /dev/sda1 = Windows Recovery partition, 500MB
  /dev/sda2 = Windows EFI partition, 100MB
  /dev/sda3 = Windows NTFS OS + Data partition, 400G
  /dev/sda4 = Linux LVM2. remainder of disk

  /dev/sdb1 = ubuntu /boot partition, xfs, 512MB
  /dev/sdb2 = ubuntu /boot/efi, 350MB
  /dev/sdb3 = Linux LVM2, remainder of disk

1. Ubuntu and Windows both boot just fine, Windows using /dev/sda2 as its EFI partition, Ubuntu /dev/sdb2 for his.

2. For some reason I needed to re-install Ubuntu exactly where it was. I slapped my DVD in the reader, boot the installer, and start. At the partman section, I leave off everything Windows-related on /dev/sda, making sure that /dev/sda2 is left at "Do not use partition". As /dev/sd[ab]2 are already tagged as "EFI partition", and that I've left /dev/sda2 at "Do not use", I'm assuming the installer would use /dev/sdb2 as /boot/efi.

Expected result is as above. Actual result follows.

3. End result: the installer leaves off /dev/sdb2 and overwrites /dev/sda2 even with a "Do not use partition flag". Subsequent boots would not see the Windows OS installed as its EFI partition had been overwritten by the installer.

4. To fix:
  a=> mount -t vfat /dev/sdb2 /mnt && cd /boot/efi && tar cf - . | (cd /mnt ; tar xf -)
  b=> cd / && umount /mnt
  c=> find a win10 boot cd, go in repair mode, reinstall EFI code+files in /dev/sda2
  d=> reboot in Ubuntu, os-prober && update-grub

Further observations:
  Other installers (Fedora's anaconda to name one) would let you specify the mountpoint of an EFI partition (yes, it should always be /boot/efi). This is not foolproof, I agree, but at least it'd leave no place to doubt on setups similar as mine as which EFI partition Ubuntu is directed to use.

--Jeff