I have a multi-system HD running in a '12 MacPro . . . two partitions for various flavors OSX, and LM 18 running at the tail end. I recently upgraded the second OSX partition to 10.12 and of course after that GRUB was broken and the LM/"windows" disk no longer showed up when booting with the option key. I did not have to use rEFInd to get the system to recognize and boot LM previously.
I have been through this before, but mostly in PPC computers where Yaboot is the linux bootloader, so GRUB seems a little different. I've read through a number of fixit posts, as well as running, "boot-repair," SG2, both of them said "successful" but, problem of not booting remains--and fiddled with Rescatux a bit today--but a couple problems remain.
I've needed to set up a separate "bios_grub" partition in the original LM install, that seems to help get GRUB installed, but, after upgrading the OSX side it seems in GParted to have wiped the data from that partition, and I can't get GParted to show an option of formatting it as "bios_grub" or anything relating to that . . . only the "ext4" or "fat32" and a few other options show up. I'm trying to avoid a re-install, since every few months OSX comes up with a security update, which will again wipe this data, so I'd like to "figure it out" if possible . . . how to get "bios_grub" flag back on that partition (10 MB).
And, from what I found on GRUB, the file to edit is /etc/default/grub . . . which I was hoping would show the root partition (which is now /dev/sda7) and/or the "boot" partition, which I believe should be the "bios_grub" partition??? but, is now "unallocated" and doesn't have an sda number; all the file shows is:
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GNU nano 2.5.3 File: /etc/default/grub # If you change this file, run 'update-grub' afterwards to update # /boot/grub/grub.cfg. # For full documentation of the options in this file, see: # info -f grub -n 'Simple configuration' GRUB_DEFAULT=0 #GRUB_HIDDEN_TIMEOUT=0 GRUB_HIDDEN_TIMEOUT_QUIET=true GRUB_TIMEOUT=10 GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian` GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" GRUB_CMDLINE_LINUX="" # Uncomment to enable BadRAM filtering, modify to suit your needs # This works with Linux (no patch required) and with any kernel that obtains # the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...) #GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef" # Uncomment to disable graphical terminal (grub-pc only) [ Read 34 lines ]