# Ubuntu – Dual boot and the files /boot/grub/grub.cfg — which one is used

dual-bootgrub2

Say, I have 2 linux systems. They both of them have /boot/grub/grub.cfg, but the one that's used on boot is from one of them. There's no /boot partition. How is it determined which /boot/grub/grub.cfg should be used and how change that?

I have 1 physical disk, 2 partitions and UEFI/GPT.

• Assuming two partitions on one physical disk with BIOS, it'll depend on who wrote to the MBR (master boot record, beginning portion of the disk) last (at install, or since you ran install-grub). They can overwrite each other if you reinstall grub. update-grub should only update the local configuration.