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So a little bit of backstory first: I originally ran a Ubuntu 18.04/Windows 8.1 Dual Boot setup and everything ran fine. But I was running into some problems regarding the space of my Ubuntu partition, so I decided to do a fresh installation of Lubuntu 20.04 to overwrite my old Ubuntu. All of the steps were successful and it installed correctly. However, after this I was unable to boot into Windows 8.1. Its filesystem was still present and I could mount it in Linux, however no matter what I did I could not get it to show up in Grub. After looking online some people recommended installation rEFInd but it wasn't finding Windows either.

Using the boot-repair utility, I got a message saying I had an installation of Windows in legacy mode(which I found out because I was booting in UEFI for my previous installation of Ubuntu and everything was fine). Trying to start my computer in Legacy mode just resulted in a black screen saying "No boot image found" or something similar .I booted a live USB and used boot-repair again,the details of which can be found here. After this I was able to boot my Lubuntu in Legacy mode but still no sign of Windows.

After this I tried using boot-repair again, grup-update and even defining a custom grub entry pointing to the partition where Windows was supposedly booting from. I tried all of these things in both Legacy and UEFI mode. I've tried just about everything I could find on the Internet but nothing worked.

My (admittedly uneducated) guess is that, while setting up the partitions during the Lubuntu install, I somehow messed up and erased/damaged something crucial to Windows booting. What I did during that step was, following the instructions, create a new root partition out of my old Linux partition and some unalocated space, as well as create an EFI System Partition(overwriting one pre-existing partition which I believed was the old Ubuntu's boot partition. If the fault is in the installation step, I'm almost sure it was due to this.

Here is the output of the output of the bootinfoscriptutility and below is the output of lsblk -f:

NAME   FSTYPE   LABEL    UUID                                 FSAVAIL FSUSE% MOUNTPOINT
loop0  squashfs                                                     0   100% /snap/chromium/1479
loop1  squashfs                                                     0   100% /snap/core/10823
loop2  squashfs                                                     0   100% /snap/core18/1988
loop3  squashfs                                                     0   100% /snap/gnome-3-28-1804/145
loop4  squashfs                                                     0   100% /snap/gtk-common-themes/1514
loop5  squashfs                                                     0   100% /snap/postman/132
loop6  squashfs                                                     0   100% /snap/rustup/617
loop7  squashfs                                                     0   100% /snap/snapd/11036
sda
├─sda1 ntfs     Recovery 62107AA6107A80B9
├─sda2 vfat              4DF5-12AD
├─sda3
├─sda4 ntfs     Acer     8C787EE3787ECC08                       49,2G    88% /home/diogor/windows
├─sda5 ext4              3619ba7c-87d2-4f85-add7-e8890a226259   16,7G    55% /
└─sda6
sr0

Thanks in advance. If any further information is required I'll be happy to provide it.

dionit
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  • Dual Boot advice:

    I suggest you read https://en.wikipedia.org/wiki/Power-on_self-test , https://en.wikipedia.org/wiki/BIOS , https://en.wikipedia.org/wiki/Master_boot_record , https://en.wikipedia.org/wiki/GUID_Partition_Table , https://en.wikipedia.org/wiki/UEFI . One will have the Answer. Read the others to understand that one.

     – waltinator Feb 18 '21 at 00:12
  • You still show the UEFI Windows partition on a gpt drive, but not any Windows UEFI boot files in the ESP - efi system partition. You also have a bios_grub partition where you must have installed in old BIOS Mode. Only use UEFI boot. Boot live installer in UEFI mode & reinstall grub in UEFI mode. Then boot Windows repair/recovery drive in UEFI mode an repair Windows.Acer Aspire E15 will not dual boot, many details Trust settings in step 35 http://askubuntu.com/questions/627416/acer-aspire-e15-will-not-dual-boot – oldfred Feb 18 '21 at 03:35
  • If you have no luck soon you can make a Fill install USB that booth bot Legacy and UEFI mode: https://askubuntu.com/questions/1300454/easy-full-install-usb-that-boots-both-bios-and-uefi. You can then boot this (in both modes), and run sudo update-grub which should add Windows to it's boot menu. If Windows then boots you know where the problem is. – C.S.Cameron Feb 18 '21 at 03:53
  • I believe you totally erased Windows booting from your EFI partition. There should be a Microsoft folder with a boot configuration file \EFI\Microsoft\Boot\BCD. You'll have to rebuild it using a Windows 10 install image. Stick to UEFI boot and follow directions from here. Only the second half of the post applies to your case. Once you're able to boot Windows, you'll have to reinstall grub from a live CD and update-grub. – zasjls Feb 18 '21 at 11:41

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