On Thu, Jul 19, 2018 at 1:16 PM Rick Stevens <ricks@alldigital.com> wrote:
On 07/19/2018 10:38 AM, Greg Woods wrote:
 what happened to me was, after the first time I booted
> Windows 10 after installing Fedora, I could no longer boot Linux

I expect that was Microsoft forcing the EFI "BootOrder' to give them
preference (boot us first if we're installed) and possibly setting the
"Timeout" to zero so the EFI selection screen isn't shown. They're
famous for that.

Yes, it doesn't surprise me to hear that. But I did think of going into the EFI boot screens and selecting the Fedora partition, and it still wouldn't load GRUB. Since I can't go back to what it looked like then, it remains unclear as to exactly what happened.
 

Reinstalling Fedora sets the parameters to a more reasonable choice. The
rule I've always used (even in the MBR days) is "if you must have
Windows on your machine coexisting with some other OS, you need to
install Windows first, reserving space for your other OS, then install
the second OS. Windows will absolutely try to take over the boot order."

True. In this case the laptop came with Windows 10 already installed, so I did something I have done many times before, which was to use gparted to shrink down the Windows partition to make room for Linux, then installed Fedora on the remaining space. The error I made on this machine was to not specify that /boot/efi should mount on the existing Windows EFI partition, instead allowing the installer to create a new one. All looked good; when I booted, I got the GRUB screen that included Windows as a selection, and I was able to boot Fedora just fine at that point. The problem came after the first time I booted Windows 10 after installing Fedora; from that point on, GRUB no longer was shown, it just went straight into the Windows boot manager. Even selecting the Fedora partition from the EFI boot screen would fail to load GRUB. The system was hosed for anything but Windows. My guess is, I could have booted from a live USB stick, copied the /boot/efi/EFI/fedora directory to the same location on the Windows EFI partition, and run grub-install with the correct incantation to re-create the GRUB image, and I could have gotten it to work without having to use the nuclear option of reinstalling Fedora.
 
The point, of course, was just to show that you can hose yourself trying to run with multiple EFI partitions. That doesn't mean it can't be done, but you really have to know what you are doing, and I didn't.

--Greg