Restore a damaged GRUB on Mac using rEFIt

restore_grub_refit.sh

#! /bin/bash

# prep and chroot into the existing system
sudo mkdir -p /mnt/root
sudo mount /dev/sda4 /mnt/root/
sudo mount -t proc none /mnt/root/proc/
sudo mount -o bind /dev /mnt/root/dev
sudo mount --bind /sys /mnt/root/sys
sudo chroot /mnt/root/ /bin/bash

# install grub and double check that the hybrid GPT-MBR is synced
apt-get install grub-pc os-prober gptsync
gptsync /dev/sda # Say YES

grub-install --force /dev/sda
#Tried sda4 (the linux partition) but didn't work

update-grub