Existing bios mode Windows install left unbootable after installing in EFI mode

Bug #1786992 reported by Phillip Susi on 2018-08-14
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
os-prober (Ubuntu)
Critical
Unassigned
partman-auto (Ubuntu)
Critical
Unassigned
partman-efi (Ubuntu)
Critical
Unassigned
ubiquity (Ubuntu)
Critical
Unassigned

Bug Description

Bugs #1668148 and #1766945 changed the installation process to install grub-efi instead of grub-pc when the installer is booted in EFI mode but the existing OS on the disk is in bios mode. Currently, this renders the existing Windows or FreeDOS install unbootable. Windows installs at least may be able to be salvaged by patching os-prober to generate a grub.cfg that still has the windows bios mode chainloader command when interpreted by grub-pc ( if the user tells their firmware to boot in legacy mode ), or to chainload the windows EFI boot loader when booting grub-efi. Normally os-prober looks for the windows bootmgr in the ESP, but in the case of a bios mode install, a copy can also be found in the windows\boot directory and at least in theory should be loadable to boot Windows even though it was originally installed in bios mode.

As things currently stand, this will be a major breakage for users in 18.10 and 18.04.1, so unless the changes to os-prober can be made in time, the other two changes should be reverted and simply stick with grub-pc in the case where the existing OS is in bios mode.

Phillip Susi (psusi) on 2018-08-14
Changed in os-prober (Ubuntu):
milestone: none → ubuntu-18.04.1
Changed in partman-auto (Ubuntu):
milestone: none → ubuntu-18.04.1
Changed in partman-efi (Ubuntu):
milestone: none → ubuntu-18.04.1
Changed in ubiquity (Ubuntu):
milestone: none → ubuntu-18.04.1
Changed in os-prober (Ubuntu):
status: New → Triaged
Changed in partman-auto (Ubuntu):
status: New → Triaged
Changed in partman-efi (Ubuntu):
status: New → Triaged
Changed in ubiquity (Ubuntu):
status: New → Triaged
Changed in os-prober (Ubuntu):
importance: Undecided → Critical
Changed in partman-auto (Ubuntu):
importance: Undecided → Critical
Changed in partman-efi (Ubuntu):
importance: Undecided → Critical
Changed in ubiquity (Ubuntu):
importance: Undecided → Critical
Phillip Susi (psusi) wrote :

To clarify, if Ubuntu is booted in EFI mode, os-prober will currently assume that grub will continue to boot in EFI mode and so refuse to add a bios Windows chainloader stanza to the menu since it will not work. It will only add a windows entry if it finds the windows efi loader in the ESP. It may be able to come up with sufficient logic to have a bios chainloader entry that is only displayed by grub-pc and hidden in grub-efi, and a corresponding EFI mode that is hidden vice versa.

That would get us out of this mess at least with Windows, though bare metal FreeDOS installs are still going to be left out in the cold.

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