Grub

Memorized boot option

  1. Modify /etc/default/grub like below
    • GRUB_DEFAULT=saved
  2. Re-generate /boot/grub/grub.cfg as root
    • grub-mkconfig > /boot/grub/grub.cfg
  3. Set your default OS to boot everytime
    • grub-set-default 0 # replace 0 with 1 for second OS, etc
  4. Set a different OS to boot into once only
    • sudo grub-reboot 1 # replace 1 with 2 if you want to boot 3rd OS

Reinstall grub

sudo mount /dev/sda2 /mnt
sudo mount --bind /dev /mnt/dev
sudo chroot /mnt
grub-install /dev/sda