For nearly all cases, I want the bootloader on a multi-boot machine to boot into the last selected option. I've had grub2 on a number of distros now and I always need to jump through hoops to get this to work properly. It looks like I need to do a couple things:
1. Edit the /etc/default/grub file and ensure the following two lines exist:
GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true
2. Update grub. For debian/ubuntu, the command is:
update-grub
for Arch/Rocky the command is:
grub2-mkconfig –o /boot/grub2/grub.cfg
Now for the hitch - on an EFI system (at least Arch and Rocky), you ALSO need to run this command (substituting the appropriate distribution name):
grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg
How to get grub2 to remember last choice?