Incomplete kernel update posted on 30 October 2016

These are quick notes about fixing my system after an incomplete kernel update.

During a system update, my workstation suddenly shut down (hardware failure). I was working on something else during the update, so I had no idea when the update was aborted. When I tried to boot again, I was greeted with this error:

Warning: /lib/modules/4.8.4-1-ARCH/modules.devname not found - ignoring.
starting version 231
ERROR: device 'UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx' not found, Skipping fsck.
ERROR: Unable to find root device 'UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx'.
You are being dropped to a recovery shell
    Type 'exit' to try and continue booting
sh: can't access tty: job control turned off
[rootfs ]#

At that time I thought that one of my harddrive died. Digging a bit into it, the partition that couldn’t be found was an encrypted one. So I thought that maybe my fstab got somehow corrupted. I didn’t have access to a shell after booting as the keyboard was not working, so I just booted with a live usb key. My disks are all encrypted, so the first step was to decrypt them:

Confirm that they are indeed crypted:

blkid | grep crypto

Decrypt/mount the partition:

cryptsetup luksOpen /dev/sdc2/ crypt

You then can’t just mount /dev/mapper/crypt. If you try, you’ll get:

mount /dev/mapper/crypthome /mnt/crypt
mount: unknown filesystem type 'LVM2_member'

Find the group of your volume (mine was main):


Find the name of the volume (mine was root):


Mount it:

mount /dev/main/root /mnt

In my case, /boot is not encrypted, so I also had to mount it to be able to look at my kernel.

mount /dev/sdc1 /mnt/boot

Then I just used chrooted:

arch-chroot /mnt

I thought that the issue might have been in the initial ramdisk environment, so I just ran:

mkinitcpio -p linux

I was greeted with quite a few warnings that some modules were not found. But all the modules for encryption was present, so I decided to just reboot. Some progress were made: I could decrypt my disk, but was then greeted with:

mount: unknown filesystem type 'ext4'

I booted on the usb key again, and looked a bit at my modules. That’s when I found that uname -r was giving me an old kernel version. Trying to reinstall the linux package was returning an error because the desc file was missing. I guess my update was interrupted during the kernel update.

Removing the package and re-installing it did the trick. Note that pacman -S --force was not enougth to prevent pacman from complaining about the missing files.

pacman -R linux
pacman -Sy linux
mkinitcpio -p linux