Cannot find GRUB configuration file
Solution 1:
Recent releases of Ubuntu have migrated to GRUB2. From the wiki:
Configuring GRUB 2
Important note: Configuration changes are normally made to /etc/default/grub and to the custom files located in /etc/grub.d. The /boot/grub/grub.cfg file should not be edited by the user; changes to this file are made by configuration scripts. After editing /etc/default/grub, you need to run sudo update-grub for your changes to take effect on the next boot.