I’m new to Linux and have been dual-booting using two separate drives; one using a LUKS-encrypted Kubuntu 25.10 (I’ve got the password) and another using Windows 10.
However, last week when I tried booting to my Kubuntu drive, my PC instead booted straight into Windows 10 and continues to do so.
Normally, it would boot into the GRUB menu where I can select between the two systems, which leads me to believe that GRUB has been destroyed, since unlocking the drive from a live USB shows an empty GRUB folder in root.
My Kubuntu install has two partitions: sdb1 (ext4, kubuntu_boot), sdb2 (luks2, root).
I’ve tried changing the boot order in my BIOS, as well as unplugging the Windows drive, but when I do this, my PC finds no bootable drive.
If it’s not possible to repair GRUB while keeping the files on the drive, is it possible to backup root to an NFTS-formatted HDD using the live USB environment, and then restoring root after reinstalling?
Hi and welcome! Since this is your first post, glad to have you here
From what you describe, it does sound like the EFI/GRUB bootloader on the Kubuntu drive is missing or no longer registered with the firmware, rather than your encrypted system being lost.
A few quick points that may help:
On UEFI systems, GRUB is usually stored on the EFI System Partition (ESP), not inside the LUKS root. If the ESP was deleted, formatted, or the EFI entry removed, the system will boot straight to Windows.
Even with LUKS, GRUB can usually be repaired from a live USB using tools like boot-repair, or by manually reinstalling GRUB after unlocking the encrypted volume.
If repair fails, yes — you can mount the LUKS volume from a live session, then copy your /home and other important data to an NTFS-formatted external drive before reinstalling Kubuntu.
I’d suggest first confirming:
Whether an EFI System Partition still exists on the Kubuntu disk
Whether the LUKS volume unlocks and your data is intact
Once that’s confirmed, repairing GRUB is often possible without reinstalling. If you share whether your system is UEFI or Legacy (BIOS) and the output of lsblk from the live USB, others here can give more precise steps.
Good luck — and don’t worry, this is usually recoverable
Lets see details on your configuration. Please copy & paste the pastebin link to the BootInfo summary report ( do not post report), do not run the auto fix till reviewed.
Use often updated ppa version with your USB installer or any working install over somewhat older ISO or run update in ISO to make it current. https://help.ubuntu.com/community/Boot-Repair & https://sourceforge.net/p/boot-repair/home/Home/
Besure to decrypt the LUKS volume before running Boot-Repair’s report or make any repairs. It has to see the install inside the volumes.
You can backup data to NTFS, not really recommended. Better to use ext4. NTFS does not support Linux ownership & permissions & you lose those. About impossible to restore for / (root) as many different ownerships & permissions. But data really only has you & one set of permissions and can be manually reset.
Posting the link to the boot repair output is your best possibility to get help. If you only have 2 partitions (boot and the / encrypted filesystem) then you probably have the Kubuntu EFI files on the windows disk, if it is an EFI install which you don’t mention. Did you select the Kubuntu drive in the BIOS?
It looks like there’s no mount point on the sdb1 partition on the device /dev/sdb, which is the drive Kubuntu is installed to. I assume this is the EFI partition you’re talking about?
I am also able to unlock the LUKS-encrypted root partition, with files that are intact.
Here’s a few screenshots of /dev/sdb from the KDE Partition Manager:
There’s a boot and a root partition (LUKS-encrypted).
Do you mean if I’ve selected the Kubuntu drive as the first boot priority in my BIOS?
When I first experienced the error, I went into my BIOS to see the boot priority. Windows had first priority, which I changed to Kubuntu, but I still couldn’t boot into Kubuntu.
Did you try to download boot repair a second time as the server may have been down temporarily? Did you try downloading it from the ubuntu site in the link posted above by oldfred?
The sdb drive appears to have boot and / (root filesystem) partitions and no EFI partition on that drive. Which drive has windows as the only drive I see that has a partition with a standard size for EFI is sdc (sdc1).
Running the command below will provide information such as filesystem type, disk label type and will show the EFI partition. That is a lower case letter L in the command.
sdc1 is apparently an unformatted partition on my internal, seperate from Kubuntu or Windows install, HDD.
This is for storage, music, videos and such.
Here are screenshots of the other partitions on it as well.
I have installed Boot Repair using these instructions.
However, when I start the app, it says “You may want to retry after mounting your encrypted partitions so that the tool can verify their contents. (cryptsetup open)”.
I have already opened the encrypted partition using Dolphin File Manager, so do I really have to do this?
Boot Repair also says that it will modify the mount point of sdc2 in order to remove spaces and special characters, but will this reformat the drive, since this is where I have all of my important files?
I’m inside of Boot Repair now.
The GRUB location, which this will supposedly repair, matches with the boot partition on my Kubuntu drive.
Any settings I should change in here, or should i just click “Apply” to repair?:
Post #3 that is what I requested. BootInto summary report.
Note that we want to see report as Boot-Repair will use a variety of default. Most case for most users those are fine. But UEFI vs old BIOS boot, or multiple installs may confuse Boot-Repair & you need specific instructions.
