Get a botched grub2.04 install back with chroot
To avoid wasting 5 hours of my life again...
Boot from a live USB...
then in a terminal :
# use su
sudo su
# mount the drive's partition on your live system
mount /dev/yourdeviceRootpartition /mnt
mount /dev/yourdeviceBootpartition /mnt/boot
mount /dev/yourdeviceEFIpartition /mnt/boot/efi
# mount the needed stuff
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
mount --bind /dev /mnt/dev
# change root
chroot /mnt
# If not network access, check /etc/resolv.conf is populated
# Reinstall grub - E.g on arch/manjaro :
pacman -Syu grub
# generate the initrd images
mkinitpcio -P linux
# update grub config file
update-grub
# leave chroot env
exit
# dont forget to umount those to avoid data corruption
umount /mnt/sys
umount /mnt/proc
umount /mnt/dev
umount /mnt/boot/efi
umount /mnt/boot
umount /mnt
# reboot
reboot
Thanks for nothing, broken manjaro update script !