I am booting four operating systems: Windows 7, Ubuntu, Kali Linux, and Linux Mint. They were installed in that order, with Linux Mint most recently and Windows 7 first. I am able to edit the /etc/default/grub file and update grub with sudo update-grub, but only configurations saved in the config file for Linux Mint are used. Is there a way to specify which configuration file grub uses or a way to set the default?
How to set default GRUB configuration file
grub2