GRUB2 UEFI SecureBoot Vulnerability: 'BootHole'
I wish the process of restoring a non-booting Debian-derived system were easier.  After needing to do it on several dual-boot systems, I keep the procedure handy now.  Here it is for posterity:1) Boot Linux from your distro CD or DVD2) Get a shell3) Mount your normal Linux partitions.  (Make sure you know where they are.  The following example assumes / on /dev/sda1 and /boot on /dev/sda2.) E.g. mount /dev/sda1 /mnt  Note: If you have a separate partition for /boot, then mount it too: mount /dev/sda2 /mnt/boot4) Mount the special nodes:  mount --bind /dev /mnt/dev && mount --bind /dev/pts /mnt/dev/pts && mount --bind /proc /mnt/proc && mount --bind /sys /mnt/sys5) Change your shell's root: chroot /mnt6) Re-install grub: grub-install /dev/sda7) Update the grub boot menu: update-grub8) Undo chroot: exit9) Unmount the special nodes: umount /mnt/dev && umount /mnt/dev/pts && umount /mnt/proc && umount /mnt/sys10) Remove media and reboot