Important file locations

configuration file:
/boot/grub/grub.cfg

configuration file used by default:
/etc/default/grub

Change the boot order

– Identify the boot partition where we want to boot by default:
cat /boot/grub/grub.cfg | grep -i 'menuentry '
For each bootable partition, we have a menuentry that identified it. We need to get the identifier we want to boot by default.
– Now, we can update the GRUB_DEFAULT="..." property defined in the /etc/default/grub file with the wished identifier.
– To apply changes, we need to execute sudo update-grub