Hello I need help with a problem configuring grub. My main OS on the system concerned is bookworm (was probably originally installed as bullseye, might even have been earlier, and then has been upgraded over the years, now at bookworm). That system is the system that has installed grub and grub's configuration gets updated whenever a kernel update happens in the Debian stable ecosystem.
I have now set up an LFS (Linux from Scratch) installation on the same box, on a brand new SSD installed into the machine for the purpose. So I want to be able to dual-boot. I have been able to get a grub.cfg including the LFS system but the root of the LFS system is being specified by device name and that is a problem. There are also a couple of existing, older SSDs in the machine, one of which contains an older installation of Debian which I don't use any more but haven't quite brought myself to delete (although will eventually), and one is mounted as /opt in my main system. Because I want to dual-boot with the LFS system I turned on the os-prober in /etc/default/grub. Running update-grub then duly finds the LFS system and sets up configuration in grub for it (it also finds the old Debian system, which I'd prefer to keep out of grub but that's not a big deal for now). Both old and current Debian installations use LVM and initrd. The LFS instance uses neither. I just don't seem to be able to persuade update-grub to put root=UUID=<blah> or root=PARTUUID=<blah> into the linux command line for the LFS system. Because update-grub is going to be run every time there is a kernel update in Debian, I need it to work and just overriding it by hand isn't a solution. Instead it is using root=/dev/sdX2. The problem is over the last few boots I have seen the SSD containing the LFS system come up as /dev/sda, /dev/sdb and on this boot now, /dev/sdc. According to the grub-mkconfig documentation[1], if I make sure GRUB_DISABLE_LINUX_UUID and GRUB_DISABLE_LINUX_PARTUUID are both set to false, in the absence of an initrd it should use "root=PARTUUID=<>" in the linux command line, but when I run update-grub that is not happening, and the device identifier is being used instead. Can anyone explain why, and how I can fix this in a way that will still work the next time the bookworm kernel gets an update? Thanks Mark [1] https://www.gnu.org/software/grub/manual/grub/html_node/Root-Identifcation-Heuristics.html#Root-Identifcation-Heuristics
