In installing most distros to be booting in UEFI mode, the program the UEFI firmware loads to boot that system gets installed in a directory on the ESP filesystem using the exact same name as every other installation coming from that root distro. To illustrate, suppose a one HDD, SSD or NVME system setup to multiboot, without any compensation during or after by the admin WRT to booting, and all sharing the same ESP filesystem, (as IMO they should, lest the UEFI firmware become hopelessly tangled in most cases):
- Tumbleweed
- Slowroll
- Leap 15.6
- Leap 16.0pre
- Fedora 40
- Fedora 41
- Ubuntu 20.04
- Ubuntu 22.04
- Ubuntu 24.04
- Debian 11
- Debian 12
- Debian 13
It wouldn’t matter in which order installed, the sorted result would be the same, the five following directories in /EFI/:
├── BOOT
├── debian
├── fedora
├── opensuse
└── ubuntu
Each of those five directories would contain as little as one file for the UEFI firmware to load. Which it would load is determined by the firmware, which can be specified within UEFI firmware setup, or software, such as efibootmgr. Exists a BBS hotkey that varies by brand that can be used to choose which of the five brands to boot. Which of each brand’s bootloader will launch will depend on which last bootloader setup got applied. Once that file is loaded, it’s up to the bootloader of the selected brand’s last bootloader setup what will be in its boot menu, Grub, systemd-boot or other, whatever. So, indirectly at least, there be 4-5 discrete starting points, depending on whether the one in BOOT actually produces a usable result.
If wishing all 12 installed systems to be directly bootable using the BBS hotkey directly, a solution I tried lies in /etc/default/grub (using Grub2, or equivalent if using systemd-boot or other bootloader(s)), on its GRUB_DISTRIBUTOR= line. Various distros populate this, or not, variously, but whatever result follows from it, empty or not, is what dictates the name of the directory in the /ESP/ filesystem, which when booted to Leap becomes /boot/efi/EFI/opensuse. In openSUSE, GRUB_DISTRIBUTOR= always defaults to opensuse if left blank by the admin. The issue is solve for me by applying a unique string value, which for the above 12 installations could (sorted) result in the following /EFI/ tree base:
├── BOOT
├── deb11
├── deb12
├── deb13
├── f40
├── f41
├── s156
├── s160
├── sslo
├── stw
├── ub20
├── ub22
└── ub24
Most of my installations are on PCs with more than 12 installations. So as not to forget to do so, the best time to assign a value to GRUB_DISTRIBUTOR= is during installation. I have yet to experience any distro enable this, but I did ask for it in Bugzilla. Next best is on first boot, followed by rerunning bootloader setup, or at least before anything else is done to cause a bootloader setup change anywhere on the computer, such installing or removing a kernel.
This setup is good even when not using the BBS hotkey to choose what to boot, as it results in no OS overwriting any other OS’s ESP entry, which can create a big mess to untangle if using encryption and/or secure boot, and undue frustration even if not.
I still use GRUB_DISTRIBUTOR= on every installation, but I don’t often boot using a BBS hotkey. Instead, I employ a one bootloader per PC scheme. Only one is required to get the job done for most installations. So far, I’ve only been using Tumbleweed’s, except on those few PCs I don’t have TW installed on. This forum thread I think adequately covers that subject. Keyword there: custom.cfg - well applies with multiple bootable physical storage devices.
HTH