I have just bumped on an issue that usually was Ubuntu’s domain (in my case ;) - my Debian ‘testing’ (buster) station has not started after a reboot… It broke after installing some updates (including kernel - 4.18-2) and rebooting the system. It stopped while trying to unlock/find swap device (which was on an encryted partition).

It seems the reason for it might be the change of device id (sda became sdb), despite the fact that I used UUIDs everywhere… Not sure if it was my fault, or Debian left something using sda in configuration of encrypted devices… Anyway - the boot just left me with the prompt of initramfs.

Knowing that the swap is the reason, I wanted to disable it (or whatever), boot the system and see how can I repair it (maybe just rebuild initramfs).

Not that simple… I do not have the Debian installation disk at the moment, so the standard rescue method does not work. I have just SystemRescueCD on my network boot, and there should be a standard way to do it with standard tools - should be enough, right?

Having some experience with rebuilding initrds in the past (eg. modifying some live systems to boot over network using NBD), I took the standard tools: gzip, xz, cpio - and got access only to something very little, containing something like microcode…

Googling I found the Debian page about initramfs, which correctly explained that the initramfs has 2 parts - the first with microcode (cpio), and the second with “standard” initrd (gzipped cpio).

Step by step how I managed to repair it:

  1. Extract the initial ramdisk 1.1. check the size of microcode initrd:
$ cpio -t < initrd-4.18-2.img
kernel
kernel/x86
kernel/x86/microcode
kernel/x86/microcode/.enuineIntel.align.0123456789abc
kernel/x86/microcode/GenuineIntel.bin
28 blocks

1.2. get standard initrd (use the size got above in skip parameter)

$ dd if=initrd-4.18-2.img of=initrd-4.18-2_initramfs.img bs=512 skip=28

1.3. extract the initramfs (in some empty directory!)

$ gzip -cd initrd-4.18-2_initramfs.img | cpio -i
  1. Fix whatever necessary (in my case I had to comment/remove swap from crypttab)
  2. Rebuild initrd
$ dd if=initrd-4.18-2.img of=initrd-4.18-2_fixed_microcode.img bs=512 count=28
$ find . | cpio -H newc -o | gzip -c > initrd-4.18-2-fixed_initramfs.img
$ cat initrd-4.18-2_fixed_microcode.img initrd-4.18-2-fixed_initramfs.img > initrd-4.18-2-fixed.img

Once again, I feel more convinced that switching to FreeBSD might be the best option in the era with Linux distros broken with systemd, unreliable/random disk ordering…

Also - encryption of things critical for system startup seem ridiculus - unless you are crazy about privacy, the operating system, programs, local system configuration should be RELIABLE, ROBUST and EASY TO ACCESS AND REPAIR(!). Encrypt only what’s worthy and do not make system startup dependent on that kind of stuff (I felt it was bad decision but thought I gave it a try - and in result I wasted time on reparing something that should give no trouble…).

  1. Debian wiki about initramfs