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When I installed Linux, the block-device-path of my root LUKS device was /dev/md125 and the unencrypted partition was /dev/mapper/md125_crypt. I have since renamed the MD device to /dev/md0, and now I'd like to rename the LUKS partition to /dev/mapper/md0_crypt. Here's what I've done so far:

  1. Replaced all references (in the various *tabs) of md125_crypt
  2. Updated my initramfs
  3. Updated grub2

However, when I reboot, my system doesn't make it to the point of asking for my decryption password; it says something about being "unable to find the root partition".

I've also tried adding a symlink (/dev/mapper/md125_crypt -> ./md0_crypt) but it doesn't seem to persist after a reboot.

How can I rename my unencrypted LUKS partition such that I can successfully boot after doing so?

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When updating your initramfs, the root partition is detected from the running system -- not from your new/renamed config values. Instead, use a live cd and chroot to set the new name.

  1. Boot into another/similar system (live/rescue cd).
  2. Do cryptsetup open /dev/md0 md0_crypt to indicate the new root name md0_crypt.
  3. Mount /dev/mapper/md0_crypt, with the partition for /boot and --bind mounts for /dev /proc /sys inside.
  4. Do chroot into the mounted md0_crypt.
    1. Edit /etc/crypttab and /etc/fstab with the new root name.
    2. Update your initramfs plus grub's kernel parameters.
    3. Double-check everything before closing the chroot
  5. Reboot into the main system.

Tested the above steps on Ubuntu 22.04, but with (instead if grub); in that case, also edit refind_linux.conf to set the new root name in the kernel parameters.

Running dmsetup rename md125_crypt md0_crypt to temporarily change the name in /dev/mapper also seems like a viable option. As-is it doesn't affect the root partition detection in update-initramfs like chroot does though.

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