On Wed, 28 Feb 2018 11:41:30 -0500 lsore...@csclub.uwaterloo.ca (Lennart Sorensen) wrote:
> On Tue, Feb 27, 2018 at 09:01:18PM -0500, Dan Norton wrote: > > Why insert itself anywhere in the first place? The machine booted > > before the installation. To start installing, the installation > > medium is placed in a CD drive or USB port and the machine is > > rebooted. During installation, other OSs are detected by the > > installer. The installer forms the grub menu with the latest > > install first and the other OSs following. Installer finishes by > > reminding the admin to remove the installation medium and it > > reboots the machine. The latest install boots unless the admin > > intervenes. Where in this process is a requirement to tinker with > > the UEFI menu? > > How are you supposed to get grub to run at all if you don't add a boot > entry for it? The grub is installed by this installer after. > > There is nothing that makes the latest install boot unless you add it > to the boot order. On legacy bios it was different because there you > just put what you wanted into the MBR boot sector and the BIOS was > typically configured to boot from the harddisk. UEFI does not work > that way. UEFI uses an explicit entry specifying which filename to > boot from which harddisk. So an entry is created specifying to boot > the grub_x64.efi file from the FAT partition containing the > bootloaders. > > Now there are some default filenames that UEFI will look for if not > explicitly told, but they are not always supported and most installers > don't use those filenames because it isn't reliable, and the explicit > entry is the official way to do it. > > The installer has no way to tell what else was on your system already > and how it booted. > OK, I think I see. Installer is not replacing something with grub, it is adding grub to the ESP, leaving anything else that might be there alone. Therefore it must make the UEFI menu point to grub. If there is something from windows, etc. there it is ignored(?). In contrast, with the primary/logical partitioning scheme it could just rewrite the mbr and let the user pick alternative systems, if any, from the grub menu. That leaves the issue of boot order, but with all the possible configurations and names for entries in the UEFI menu, putting the latest first instead of trying to parse all that stuff makes sense. Taking a look at what efibootmgr reports... # efibootmgr BootCurrent: 0000 Timeout: 9 seconds BootOrder: 0003,0001,0002,0000,0004,0005,0006 Boot0000* debian Boot0001* USB Floppy/CD Boot0002* USB Hard Drive Boot0003* ATAPI CD-ROM Drive Boot0004* Unknown Device Boot0005* USB Floppy/CD Boot0006* Hard Drive ...but, if you go into the setup menu on my PC (POST -> Esc) you see some 'UEFI Boot Sources' and some 'Legacy Boot Sources' with common items. However, 'debian' is exclusively in the UEFI list and 'Hard Drive' is exclusively in the Legacy list. One cannot be moved to the other. If 6 were put first in the boot order or made current, it might try to legacy boot windows, but windows is long gone. This disk was cleaned off and several debian distros installed with the GPT and LVM schemes. Thanks very much everybody. - Dan
