On Mon, Apr 4, 2016 at 5:49 AM, Gianluca Cecchi <gianluca.cecchi@xxxxxxxxx> wrote: > Hello, > I have a nuc6i5 where I have 2 SSD disks. > The M.2 one (250Gb) is seen as sdb, while the sata one (500Gb) as sda. > Initially I have installed f23 on the one seen as /dev/sdb and I presume the > boot loader has been installed on it, correct? How to check? mount | grep sdb You should get back several things, one of which will be something like this (partial snippet) /dev/sdb1 on /boot/efi That's where the bootloader lives on a NUC since it has UEFI firmware. The tl;dr for everything that follows is: you're probably fine just keep on doing what you're doing. Just don't ever run grub2-install from either distro. > > With my surprise CentOS 7 made all in a fantastic way, in the sense that > during the partitioning part it recognized the fedora 23 partitions and its > lvm parts and without asking anything (actually there was no option to > manage grub configuration at all...) it configured its (I think) grub2 so > that the menu contains also the fedora 23 lines (normal one and one labeled > as "Advanced options for Fedora 23...") and they work as expected > > So far so good, it went better than I imagined... I'm *pretty* sure this is working out OK because the NUC doesn't have Secure Boot enabled by default. Mine didn't, as it didn't come bundled with Windows. Even enabling Secure Boot didn't work either, I had to use the option in the firmware to download a certificate/key and now it's working. I have no idea how this works on CentOS because I haven't tried it. But this multiboot Secure Boot issue came up on the openSUSE list just last week, and the shim.efi used by each distro of course only contains the key for that distribution. So chainloading from one GRUB to another doesn't work anymore, nor would even using configfile to just read the other distro's grub.cfg. Instead what you have to do is use the firmware built-in boot manager to choose the distro you want to boot, which selects the shim+grub combination for that distro. The two alternatives are: a.) go down the deep dark rabbit hole of mokutil, extracting the key for each distro and loading it into the other distro bootloader. I read a bit how to do this and just gave up, using the built-in boot manager is much easier. b.) possibly even easier is using efibootmgr to either persistently change the boot order, or to do a one time boot using boot next. That options -o and -n respectively. > > Now I have a kernel update proposal for Fedora 23 and I have not applied it > because I don'tknow if it can break anything or not (eg replace grub > configuration or so on...) > ANd the same doubt would be when a CentOS 7 new kernel will be available. The bootloader configuration file is updated with a kernel update. This is done by grubby. And it only updates the distro specific bootloader configuration file. That means you will not see the new kernel for CentOS if you depend on booting CentOS with Fedora's GRUB. Likewise you don't see the new kernel for Fedora when using the CentOS GRUB. To fix that you need to run grub2-mkconfig from each distro to recreate the grub.cfg from scratch, making sure you using -o to point it to the correct location on /boot/efi/ for each distro. Or again, just give up on multiboot and GRUB, and use the firmware built-in bootloader or efibootmgr to switch between distros. In theory it's easier to fix bugs in software than firmware, and to depend on GRUB for multiboot, but the reality is, it's a crap Ux. I hate it. It's a failure. It's a failure upstream. It's a failure by the distros. They've all done it wrong. And there's pretty much zero interest by anyone in fixing it. Plus adding on Secure Boot it's actually pretty ugly and difficult to fix. As for the bootloader binaries themselves, those are updated by the distro specific packages shim and grub2-efi. Those aren't often updated, but any normal update you do could include those and they will update the bootloader binaries on /boot/efi - this is functionally equivalent to grub2-install being run automatically on a BIOS system. Note that you shouldn't ever run grub2-install on a UEFI system, so definitely purge that habit as soon as possible. -- Chris Murphy -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: http://lists.fedoraproject.org/admin/lists/users@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
