On Fri, 27 Sep 2019 at 09:13, Peter Humphrey <pe...@prh.myzen.co.uk> wrote: > > On Thursday, 26 September 2019 16:44:10 BST Mick wrote: > > On Thu, 26 Sep 2019 at 15:47, Peter Humphrey <pe...@prh.myzen.co.uk> wrote: > > > On Thursday, 26 September 2019 10:16:54 BST Adam Carter wrote: > > [Snip interesting stuff] > > > > > I got the impression that I would be able to UEFI boot from multiple > > > > different devices, eg a USB drive with UEFI as well as the hard disk. > > > > I may be wrong, but I don't think this is possible (yet?). You could > > use a secondary bootloader, e.g. GRUB, other than the UEFI firmware to > > load OS kernels wherever they might be positioned on the system. > > But see next: > > > > Oh yes, removable devices can be booted, but not secondary, internal hard > > > drives. Apparently. On this system. Today. > > I can boot from USB or CD drives by entering the UEFI BIOS at boot and > selecting the one I want to boot from - and this BIOS dates from 2014. I doubt > this is unusual.
Sorry, my mistake - the following is what I meant to write, but in a rush I failed to do so: As long as you structure the ESP filesystem as per UEFI specification, a sympathetic OEM UEFI firmware implementation will process the first ESP on the first hard disk and list OS kernels it finds in its boot manager menu for you to select from. The latest UEFI specification does not restrict the number of ESPs, or their location. It is unlikely the UEFI firmware will process additional ESPs on the same, or other hard disks, or partitions which have anything other than FAT(12,16,32) filesystems. I seem to recall earlier OEM implementations explicitly excluded more than one ESP on the primary disk. In the future the UEFI specification may evolve to include more than one ESP or FAT partitions, perhaps even with/without the ESP GUID being set. Removable devices with an ESP structured as per UEFI specification will also be probed and their primary (default) bootable kernel listed by the UEFI firmware. Selecting a listed removable device from within the UEFI boot menu will boot it, as you observed. If you want more than one kernel per OS subdirectory to be listed in the UEFI boot manager's menu, you will need to add them in the desired order using the efibootmgr command. Otherwise, the UEFI firmware will not behave predictably in which of these kernels it selects to list in its boot menu. As I understand it, 'bootctl --update' can be used to update systemd-boot boot manager's menu and it is looking for bootable kernels by scanning /efi, /boot, and /boot/efi, or the directory set by passing the '--path' option to it. Manual addition of bootable kernels must be set via /loader/entries/*.conf (one file per kernel image) and then setting the default kernel to be booted in /loader/loader.conf. I find all this to be unnecessary complication for maintaining a boot manager manually, compared to using say efibootmgr. However, it is handy to be able to press 'e' to edit the default entry at boot time, or if new kernels are always stored where expected by the scripts of binary distros. For Peter's use case, OS and kernel resides on secondary disk, the solutions I can think are: 1. Use GRUB. The UEFI firmware will load the GRUB efi image, which will load the desired kernel and OS wherever it might reside. Secondary disks and non-FAT filesystems are not a problem, because GRUB has various fs drivers and will probe additional devices. Following installation maintenance is minimal compared to other options. 2. Use systemd-boot. Copy each kernel from the secondary disk to /boot/EFI/ creating the corresponding /loader/entries/*.conf, adding the kernel .conf name and the OS root partition's path on the secondary disk. The root path can also/instead be included in the kernel itself (CONFIG_CMDLINE). 3. Use some other boot manager (e.g. rEFInd, ELILO). 4. Use efibootmgr after you copy the kernel from the secondary disk to the ESP in a corresponding OS subdirectory. The root path should be included in the kernel. I hope the above clarifies my previous post. -- Regards, Mick
