How to reinstall grub from a liveUSB if the / partition is encrypted and there is a separate /boot partition?

Solution 1:

1. Boot from an Ubuntu Live USB with a working internet connection.

2. Open a Terminal window (Applications → Accessories → Terminal).

3. Type the following commands (pay attention to the comments, starting with #, after some commands):

   sudo -i
   apt-get update
   apt-get install cryptsetup lvm2
   fdisk -l
   cryptsetup luksOpen /dev/sda? TAG           # sda? is your root partition
   vgchange -ay
   vgscan
   vgchange -ay [VOLUME GROUP NAME]           # From the above command
   lvscan
   mount /dev/[VOLUME GROUP NAME]/[LOGICAL VOLUME NAME] /mnt          # LOGICAL VOLUME NAME from above command
   modprobe efivars
   mount /dev/sda? /mnt/boot/efi          # sda? is your efi partition
   mount --bind /dev /mnt/dev 
   mount --bind /dev/pts /mnt/dev/pts
   mount --bind /proc /mnt/proc
   mount --bind /sys /mnt/sys
   cp /etc/resolv.conf /mnt/etc/
   chroot /mnt
   

   then do

   apt-get install --reinstall grub-efi-amd64
   

   or

   apt-get install --reinstall grub-efi
   

   and continue with

   update-grub
   umount /mnt
   vgchange -an
   cryptsetup luksClose TAG