## Configuration File sudo find /boot -name "grub.cfg"
## List Menu cat /boot/grub/grub.cfg | grep 'menuentry ' | cut -f 2 -d "'" | nl -v 0
0 Ubuntu 1 Ubuntu, with Linux 5.15.0-1035-gcp 2 Ubuntu, with Linux 5.15.0-1035-gcp (recovery mode) 3 Ubuntu, with Linux 5.13.0-48-generic 4 Ubuntu, with Linux 5.13.0-48-generic (recovery mode) 5 UEFI Firmware Settings
sudo grub-reboot 3 #sudo grub-set-default 3
sudo reboot
sudo vi /etc/default/grub
#GRUB_DEFAULT=0 GRUB_DEFAULT=3
sudo update-grub