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I’m experiencing a trouble with my dual-boot windows and Debian ASUS PC.

Everything worked fine until a weeks ago when I entered into MS-windows after some months that I didn’t. The PC then booted directly into MS-windows, later when I restart, and enter the boot menu, if I select Debian boot it goes into the advanced setup menu of ASUS booting. I then restored the grub, following the instructions for Debian and everything worked fine again, but if I enter into windows it happens again.

The only thing, when I do a “boot-install —recheck /dev/sda” from chroot it just tells me that the /efi/debian/grubx64.efi is a read-only file.

  • fwiw, I was always told to install Windows first, then a second OS, because Windows will attempt to take over everything by rewriting boot code. – Rob Dec 27 '18 at 12:57
  • Yes, windows was already installed and I put Debian later – cccnrc Dec 27 '18 at 13:05
  • “The PC then booted directly into MS-windows and when I enter the boot menu at restart,… ” do you mean “The PC then booted directly into MS-windows, later when I restart, and enter the boot menu, …”? – ctrl-alt-delor Dec 27 '18 at 13:19
  • @ctrl-alt-delor thanks a lot for your reply. Yes, I mean that when I later reboot and enter the boot menu (press ESC), if I select “Debian”, it does not start and goes straight to the “advanced menu” (like if I press F2 when PC reboot) – cccnrc Dec 27 '18 at 13:24
  • @ccc.nrc I updated your question for you (you can also do this). – ctrl-alt-delor Dec 27 '18 at 13:27
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Solved. I finally reinstalled GRUB through debian rescue mode from USB (as explained in https://wiki.debian.org/GrubEFIReinstall) and then, once rebooted and entered in my debian OS (and connected to a network), I re-installed the updated grub: apt-get install --reinstall grub-efi

At this point, I don't know exactly why, but if I asked the efi boot entries with:

efibootmgr --verbose

it showed 4 entries:

  • boot0000* debian on HD pointing to file \EFI\debian\grubx64x.efi
  • boot0001* Windows Boot Manager on HD pointing to file \EFI\DEBIAN\GRUBX64.EFI
  • boot0002* Windows Boot Manager on HD pointing to file \EFI\MICROSOFT\BOOT\BOOTMGFW.EFI
  • boot0003* UEFI (my USB with debian): note that it was inserted during installation and chroot session but no longer inserted.

So I supposed that it probably didn't "update weel" the boot entries and so I did:

sudo update-grub

and now everything goes well and if I ask for boot entries (efibootmgr --verbose):

  • Boot0001* Windows Boot Manager on HD pointing to file \EFI\DEBIAN\GRUBX64.EFI
  • Boot0002* Windows Boot Manager on HD pointing to file EFI\MICROSOFT\BOOT\BOOTMGFW.EFI

Do not know exactly what happened, if somebody got a clue is welcomed!

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