Minimal instructions for kernel downgrade on arch linux with full system encryption using dm-crypt and luks

arch-linux-encrypted-kernel-downgrade

# Kernel downgrade on ARCH Linux with encrypted file-system
#
# assumes you followed https://gist.github.com/mattiaslundberg/8620837 to set up your system
#
# Credits: 
# https://stephentanner.com/restoring-grub-for-an-encrypted-lvm.html 
# https://wiki.archlinux.org/index.php/Kernel_Panics

# Boot into archiso live USB

# load the dm-crypt module
modprobe dm-crypt

# decrypt the root partition
cryptsetup luksOpen /dev/sda3 linux
# run `vgscan` to verify, should produce output similar to
# `Found volume group "vg0" using metadata type lvm2`

# activate logical volumes
vgchange -a y vg0
# `3 logical volume(s) in volume group "vg0" now active`
# verify with `lvscan`

# mount the root partition
mount /dev/vg0/root /mnt

# change root
arch-chroot /mnt /bin/bash

# mount boot partition
mount /dev/sda2 /boot

# list previous kernel versions in pacman cache
find /var/cache/pacman/pkg -name "linux-4.*"

# downgrade to a previous kernel version
pacman -U /var/cache/pacman/pkg/linux-4.xx-x.pkg.tar.xz

# exit and reboot
exit
reboot