grub-editenv
Edit GRUB environment variables. tldr-pages
On Linux
Linux
Set a default boot entry (Assuming the boot entry already exists)
grub-editenv /boot/grub/grubenv set default=UbuntuIdentifyDisplay all GRUB environment variables
grub-editenv /boot/grub/grubenv listIdentifyReset the saved_entry variable to the default
grub-editenv /boot/grub/grubenv unset saved_entryIdentify