Q for Linux gurus: recreating EFI boot partition

In My Humble Opinion
1

In a stunning display of stupidity, I managed to delete my boot partition. I wanted to reformat an old Kubuntu 22.04 live USB stick. When I ran the partition manager to remove the old partitions, I didn’t pay attention to what drive was selected… and here we are. This happened on Monday night, and I haven’t had to reboot my computer yet, but I can’t keep this up forever.

I run Kubuntu 24.04 LTS. It is the only OS on my system. My primary hard drive is 500 GB, which contains the OS and the aforementioned boot partition. My secondary drive is 6 TB and contains my home partition.

I want to recreate the partition without having to reinstall the whole OS. Having to do so wouldn’t be as devastating as it would if I was running Windows, but it would still be a pain in the ass that I’d rather avoid.

I’ve been reading this article:

https://www.baeldung.com/linux/efi-boot-partition-restore

Since I’m only running a single OS, I like the last option, #6: skip GRUB altogether. I’ve got bootable USB sticks for both Kubuntu 24.04 LTS and rEFInd, so I should be good if anything (else) ever goes wrong.

I’ve recreated the partition, flagged it as boot, and set the mount point to /boot/efi. If I’m understanding the article correctly, I need to create an entry in efibootmgr, and… that’s it? The article says nothing about mounting the boot partition and copying/installing anything there. The article seems to be saying if there’s no bootloader in /boot/efi, the system will boot via the firmware? So I’m supposed to just leave the partition empty? Do I have this correct? That just seems wrong.

I really want to be confident that when I reboot the machine, things will go smoothly!

2

I only skimmed through that article. One thing I see missing is setting your partition type to “EFI System”, which should be the very first type option in fdisk.

Here is what I would do. I think you’ve already done some of them.

  1. Use your favorite partition manager, such as fdisk or gparted to recreate the EFI partition.
    1. It should be 1GB or so in size
    2. It should be set with the type “EFI System”
    3. It should be formatted FAT32/vfat
  2. Mount the partition at /boot/efi
  3. Run grub-install /dev/sda (or /dev/nvme0n1 or whatever)—that should copy the appropriate files into /boot/efi and add an entry to the EFI boot variable list
  4. Just for good measure, run update-grub.
  5. Run efibootmgr all by itself
    1. That should show the existing boot list
    2. Look at the BootOrder: line
      1. The entry will be something like 0007,000A
      2. 0007 corresponds to the entry in Boot0007
    3. Check the appropriate boot entry to make sure it points at what you want
      1. It should be something like Boot0007 Ubuntu HD(1,GPT,[…]./\EFI\ubuntu\grubx64.efi
      2. The “[…]” will be a unique ID that you can get by running blkid -p -o value -s PART_ENTRY_UUID /dev/sda1 (or whatever your EFI partition is numbered
  6. Reboot and hope it works?

I’m not quite sure I understand what you mean when you say you want to avoid grub altogether. Do you mean you want a different boot loader than grub? I recommend getting the system booting with grub, and then switch to a different boot loader, but that’s only because I know much more about grub.

Or, do you mean that you want to setup a rescue USB stick to get your system booted in the event you’re install doesn’t go correctly? Yes, that should not be difficult to do. Again, I know more about setting up a rescue with grub than rEFInd.

If you have to boot from a rescue USB drive, that shouldn’t be too terrible. Run cat /proc/cmdline and take a picture of it, or note it down. That will tell you exactly what options you need to boot your system the way it is now. Also take a look at /boot/grub/grub.cfg and look for the first entry that starts menuentry, and pay attention to the linux and initrd entries under there. You might have to type those into grub by hand on the rescue disk.

This is for grub:

  1. Boot the rescue disk
  2. At the grub menu press a key (I forget which) to get a command line
  3. Type linux (hd1,gpt2)/boot/vmlinuz then all that stuff you noted earlier
    1. It might not be (hd1,gpt2), but you can use TAB completion to get grub to list the available options, and should be able to sort out the exact path
  4. Type initrd (hd1,gpt2)/boot/initrd.img
  5. Press F10 to make grub boot
  6. Don’t get upset when it fails, go back and try again.

Linux is not Windows, the situation you’re in is completely recoverable without touching your root partition, the only trick is finding the way to fix things that works best for you.