Fixing initramfs initrd.img on Devuan

From a live CD as root, tested on Devuan:

#nvme0n1p3 is my LUKS encrypted root partition. It's not using LVM.

cryptsetup open /dev/nvme0n1p3 root_fs    #or whatever name you see in your crypttab

mount /dev/mapper/root_fs /mnt
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
mount /dev/nvme0n1p2              #if you have a separate boot partition
chroot /mnt

If your /etc/fsstab has wrong UUIDs fix them and then run update-grub.

mkinitramfs -o /boot/initrd.img-4.19.0-18-amd64 4.19.0-18-amd64

If the above throws any warning, /etc/cryptsetup-initramfs/conf-hook has a setting you can change to always include crypto capabilities in initrd.img. Change it and retry mkinitramfs.