This is a list of some common issues that I’ve had while running through this process and how to get out of them. It is by no means exhaustive, but I’ll do my best to keep it up-to-date as I go through this more.

Fix EFI Partition Mapping

TODO

Reinstall Linux Image

If you’ve accidentally deleted the initrd.img and/or vmlinuz files from the boot partition (or forgot to move them from the boot partition while removing it) you just need to find the kernel versions that are currently installed and reinstall them.

We can get the kernel version from symlink at the root of the filesystem for either the initrd.img or vmlinuz files:

ls -l /

...
lrwxrwxrwx   1 root root    30 Feb  2 17:46 initrd.img -> boot/initrd.img-6.1.0-17-amd64
...
lrwxrwxrwx   1 root root    27 Feb  2 17:46 vmlinuz -> boot/vmlinuz-6.1.0-17-amd64
...

If you look in the path of the file that it is symlink’d to you should see the version and CPU architecture of the Linux image. In this case, my kernel version is 6.1.0-17 and architecture is amd64. We’ll need those pieces of information when installing the kernel again.

Now that we have the kernel version, we can reinstall the appropriate Linux image packages:

apt-get install --reinstall linux-image-6.1.0-17-amd64

If you can’t seem to find yours, try checking the apt-cache to find which linux-image package needs to be installed:

apt-cache search linux-image-

Chroot Into OS

We can get back into our OS if it’s failing by using either a live Linux distro (like Ubuntu), or another Linux distro running on your machine. Once you’re in that environment, unlock your LUKS-encrypted root filesystem under the name debian_root (or whatever you want the unlocked drive to be called):

cryptsetup luksOpen /dev/sda3 debian_root

Then, we can mount the mapped partition as normal:

mount /dev/mapper/debian_root /mnt

Finally, mount the other (possibly two) partitions by checking the /etc/fstab from within the Debian root filesystem:

mount /dev/sda1 /mnt/boot
mount /dev/sda2 /mnt/boot/efi # or /efi depending on what's in your fstab

With all of our partitions mounted we can chroot into the Debian OS (if needed) to be able to run commands, install packages, etc. using:

chroot /mnt

Now you can do what you need to do within your Debian OS. When you’re done make sure to exit as you can’t restart the machine from inside a chroot session.

Note
You can also provide a second argument for what command to run using chroot. For example, if the shell in your current Linux distro doesn’t exist inside your Debian one you may need to add bash as an argument.

Kernel Module Signing Issues

When I have issues with signing a new Linux kernel module, I’ve found it helpful to understand how kernel modules are created. For that check out the Build a Simple Linux Kernel Module post.