August 24, 2018 - Reading time: 3 minutes

Mount the partition your Ubuntu Installation is on. If you are not sure which it is, launch GParted (included in the Live CD) and find out. It is usually a EXT4 Partition. Replace the XY with the drive letter, and partition number, for example: sudo mount -t ext4 /dev/sda1 /mnt.

sudo mount -t ext4 /dev/sdXY /mnt

Now bind the directories that grub needs access to to detect other operating systems, like so.

sudo mount --bind /dev /mnt/dev && sudo mount --bind /dev/pts /mnt/dev/pts && sudo mount --bind /proc /mnt/proc && sudo mount --bind /sys /mnt/sys

Now we jump into that using chroot.

Now install, check, and update grub.

This time you only need to add the drive letter (usually a) to replace X, for example: grub-install /dev/sda, grub-install –recheck /dev/sda.

grub-install /dev/sdX grub-install --recheck /dev/sdX

Now grub is back, all that is left is to exit the chrooted system and unmount everything.

exit && sudo umount /mnt/sys && sudo umount /mnt/proc && sudo umount /mnt/dev/pts && sudo umount /mnt/dev && sudo umount /mnt

Shut down and turn your computer back on, and you will be met with the default Grub2 screen.

July 23, 2018 - Reading time: ~1 minute

BusyBox v1.18.5 (Ubuntu 1:1.18.5-1ubuntu4) built-in shell (ash) 
Enter 'help' for a list of built-in commands.

(initramfs) exit

/dev/mapper/ubuntu--vg-root: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY.
(i.e., without -a or -p options) 
fsck exited with status code 4. 
The root filesystem on /dev/mapper/ubuntu--vg-root requires a manual fsck. 

BusyBox v1.18.5 (Ubuntu 1:1.18.5-1ubuntu4) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) fsck /dev/mapper/ubuntu--vg-root -y

fsck from util-linux 2.27.1
e2fsck 1.42.13 (17-May-2015)
/dev/mapper/ubuntu--vg-root contains a file system with errors, check forced.

BusyBox v1.18.5 (Ubuntu 1:1.18.5-1ubuntu4) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) reboot

November 18, 2016 - Reading time: ~1 minute

sudo apt-get install grub-emu

Then in terminal execute

grub-emu