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Is it possible to having installed Windows 10 and Ubuntu reformat 100MB Efi partition and 2MB BIOS boot partition to make everything grub/efi work? Also is it possible to remove or see the content of /dev/sda where is grub installed? I have such situation, have all partitions with installed Windows and Ubuntu + Windows recovery and Windows restore partitions but bios stopped to see the hard drive in bios boot options (It detects the hard drive as hardware with all model info, etc) and only see in boot options DVD and aditional USB if attached.

I have all set on Efi boot partition and have issues with make it work so addidtionally created 2 MB of legacy BIOS boot partition but not sure what should be placed there? Grub2 i386 image? So...there is grub installed on /dev/sda, Efi partition with efi grub and boot/windows/ubuntu efi files and bios boot partition empty...what can I do to try to make the bios see again hard drive filesystem to choose or just boot options based on hard drive? grub.cfg seems to be properly configured

  • How you boot install media UEFI or BIOS/CSM is then how it installs. And you do not specify use of ESP - efi system partition as it is automatically used with UEFI install. Or if BIOS/CSM install the bios_grub partition is used. The bios_grub only used with BIOS installs is unformatted and shown as an error in gparted (as it has no format). What brand/model system. You must use 64 bit installer if UEFI system. help.ubuntu.com/community/UEFI & askubuntu.com/questions/221835/… – oldfred Mar 4 '18 at 17:11
  • I've managed to start installed Ubuntu on hard drive by starting liveUSB session -> when grub menu appears i press 'c' to get into grub prompt-> set root=(partition with installed ubuntu), set prefix=(partition with installed ubuntu) /boot/grub, insmod normal, normal ('enter' after each) -> I get proper grub menu with Windows and Ubuntu but only section 'advanced Ubuntu settings' and from there pressing latest linux kernel 4.13.36 generic starts the system properly...so, it seems it's fine but after reboot again all procedure to be done...no bootable options in bios other than DVD and USB – PawełG Mar 4 '18 at 17:45
  • What brand/model system? Can you try booting from UEFI menu with flash drive removed? – oldfred Mar 4 '18 at 20:13
  • Asus X750JB, I cannot boot without USB or DVD live Ubuntu or Windows, may start only linux installed distro via grub prompt, have no idea how to do it with Windows. Thinking about erase whole disk and create new partition table or send laptop to after guarantee meintenance... – PawełG Mar 5 '18 at 7:03
  • oh, and I probably can boot only in uefi mode (but strong maybe here), in other mode even when liveusb is plugged it shows 'please attach another boot device' or something similar like boot partition not found. It just lost some info between bios and hard disk (MBR issue?)...I've used boot-repair without any effects and Rescatux which messed all this, due to Rescatux use I've lost HDD boot options in bios trying all available options this program offers. – PawełG Mar 5 '18 at 7:04

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