EFI, BIOS boot incompatability?: Grub2 does not recognize Windows Boot (EFI) after Fedora 25 (BIOS) install

asked 2017-03-05 20:31:25 -0500

nipper gravatar image

updated 2017-03-05 21:22:15 -0500

florian gravatar image

The goal was to have a dual boot machine, Windows 10 and Fedora 25.

However, the machine is for a family member who has to run a number of GIS programs, one of which is only available in Windows, so the default fall back position is to return to Windows 10 only.

Questions: Is Grub2 Fedora BIOS boot incompatible with the Windows EFI boot process? (Note the last DATA, EFI variables are not supported on the system).

  • If not, how do you I suggest I modify Grub2 to recognize Windows 10 boot?

    • Is the Windows boot in /dev/sda3 or /dev/sda2?
  • If so, do you agree that the windows install looks intact?

    • if so will GParted removal of the Fedora partitions from the USB drive result in a Windows 10 boot?

    • Can I resize the /dev/sda5 Windows Basic Data partition from the removed Fedora partitions without harm?

Machine information and configuration:

The hardware is an Asus Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz with a single 1 TB hard drive, and 21 GB RAM.

uname -a: Linux name.localdomain 4.8.6-300.fc25.x8664 #1 SMP Tue Nov 1 12:36:38 UTC 2016 x8664 x8664 x8664 GNU/Linux

It arrived with Windows 10 installed and I wanted to add Fedora 25 as a dual boot.

I used a USB stick with Fedora Media Writer and the Fedora 25 workstation image. I had to reconfigure the UEFI settings for the USB to be recognized at boot.

Instead of my normal approach (manual installation) I told the install program to resize /dev/sda5 NTFS Basic Data partition and to automatically partition and install Fedora.

Upon reboot only Fedora and Fedora rescue were recognized by Grub2. Windows 10 was not. Fedora seems to be working quite well.


The "Disk" output summary:

Device/ Partition Type/ Contents/ Size MB (bytes)

  • /dev/sda1/ EFI System/ FAT (32-bit Version)- Not Mounted/ 105 (104,857,600)

  • /dev/sda2/ Microsoft Reserved/ Unknown/ 17 MB (16,777,216)

  • /dev/sda3/ Basic Data/ NTFS – Not Mounted/ 161 (161,061,273,600)

  • /dev/sda4/ Microsoft Windows Recovery Environment (System)/ NTFS –Not Mounted/ 524 (524,288,000)

  • /dev/sda5/ Basic Data/ NTFS – Not Mounted/ 462 GB (462,102,200,320)

  • /dev/sda6/ BIOS Boot/ Unknown/ 1.0 MB (1,048,576)
  • dev/sda7/ Linux Filesystem/ Ext4 (version 1.0) – Mounted at /boot/ 1.1GB (873 MB free (18.7% full)

  • /dev/sda8/ Linux Swap/ Swap (version 1) – Active/ 6.3 GB (6,335,496,192)

  • /dev/sda9/ Linux Filesystem/ Ext4 (version 1.0) – Mounted at Filesystem Root/ 54 GB = 46 GB free (13.8% full)

  • /dev/sda10/ Linux Filesystem/ Ext4 (Version 1.0)- Mounted a /home /315 GB-310 GB free (1.7% full)

So it appears that the Windows 10 partitions (sda2-5) are intact.

The fdisk -l output: root@name grub2]# fdisk -l

Disk /dev/sda: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical ...
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If you have Win10 installed in (U)EFI mode, why did you install Fedora in BIOS?? Just reinstall Fedora using an EFI install (use your current Fedora and use dd to create an efi-compatible USB boot drive). Grub2 is of course capable of dual-booting Win10 and Fedora25.

During Fedora install, make sure you are using the existing ESP (around 100MB) and set the mount point to /boot/efi, without reformatting.

florian gravatar imageflorian ( 2017-03-05 21:15:09 -0500 )edit