Background: Dual booting windows 10 and lubuntu 18.04 from single ssd, both in EFI boot. No separate /boot partition. Secure boot is disabled. Can load grub from live-USB ubuntu fine (boot order is configured correctly).
TLDR: Reset BIOS to defaults. Now grub menu won't appear/I boot straight to windows. Most popular methods of grub-install and boot-repair have failed me, so has reinstalling ubuntu. See last link for boot-repair pastebin link.
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I recently reset my BIOS options back to their defaults while fixing an different problem with my Ubuntu 18.04. However, on rebooting I found that I load straight to windows without the grub menu appearing. After a some research, the following links:
How can I repair grub? (How to get Ubuntu back after installing Windows?)
https://howtoubuntu.org/how-to-repair-restore-reinstall-grub-2-with-a-ubuntu-live-cd
and a few others all seem to suggest some variant on mounting the linux partition, running chroot and installing grub again. Despite attempting this several times and following these guides precisely, every time I would reboot after grub installed I would still be taken straight back to windows on boot.
I stumbled on other articles suggesting that an incompatibiltty between the boot modes (MBR vs. EFI) of each OS might be the problem, but I believe they are both EFI.
For what it's worth, I also tried this method:
https://teczuz.com/rescue-repair-reinstall-grub-boot-loader-ubuntu/
which relies on using the Ubuntu server installation live USB expert mode to repair/rescue grub, however I have been unable to access the "other options menu" via F6 after the language selection (perhaps they removed this functionality in new versions since the release of the article?).
Eventually I decided to do a complete reinstall of ubuntu hoping that would fix the problem, but I still have the same issue.
Other sources still have advised I try the recommended repair feature of boot-repair. After installing and running boot-repair, I receive the message "An error occurred during the repair". Here is the pastebin link describing the repair/diagnosis (i.e. the "BootInfo summary"):
http://paste.ubuntu.com/p/GKdgWjBJwz
Rebooting after boot-repair still went directly to windows with no grub menu. It is perhaps worth noting that after boot-repair was finished running, they instructed me to ensure that my BIOS boots on sdb2/EFI/ubuntu/shimx64.efi file and to change the boot order in the event that I boot straight to windows. I am unsure how I would go about verifying the former, and I am unclear on what the latter has to do with my grub not loading (even though my boot order is currently set up so that all USB and CD ROM images boot first).
I greatly appreciate any light anyone could shed on the issue.
