GRUB won't recognize Window 7 on different HDD in Laptop

Question

The link in the "duplicate" is too specific to that user's issue to be of any help to me. When I run that answer, I get:

grub-probe: warning: disk does not exist, so falling back to partition device /dev/sda1.
grub-probe: warning: disk does not exist, so falling back to partition device /dev/sda1.
grub-probe: warning: disk does not exist, so falling back to partition device /dev/sda1.
grub-probe: error: disk `hostdisk//dev/sda1' not found.

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As a preface I have this laptop, albiet a few years old now, which is very bad at playing nice with anything other an Windows 8: https://www.asus.com/Notebooks/ASUS_ROG_G750JX/overview/

I've tried dual booting off the same drive in the past, and it hasn't worked out for me on this machine for whatever reason. So this time, I caved and decided to split them up.

I've for Ubuntu 14.04 LTS on a 1TB HDD (/dev/sda), and Windows 7 Ult (x64)(/dev/sdb) on a 250GB SSD. Both appear in the BIOS as boot options, with the Ubuntu drive being set as the default.

My only gripe, is that currently the only way into Windows is to let the Laptop boot to GRUB, then select System Settings, so that it reboots directly into the BIOS, and then select my Windows SSD from the boot override page.

I've been told millions of times that GRUB would simply find my Windows OS after doing a 'sudo update-grub' but it never has.

All I want is to be able to boot to Win7 directly from GRUB

And yes, I followed all the normal dual boot procedure, despite being on separate drive (ie. Windows first, then Ubuntu, made sure the Windows drive was plugged in at the time, etc.).

I would greatly appreciate any helpful responses.

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lsblk output:

NAME                         MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda                            8:0    0 931.5G  0 disk 
├─sda1                         8:1    0   512M  0 part /boot/efi
├─sda2                         8:2    0   244M  0 part /boot
└─sda3                         8:3    0 930.8G  0 part 
  ├─ubuntu--vg-root (dm-0)   252:0    0 914.9G  0 lvm  /
  └─ubuntu--vg-swap_1 (dm-1) 252:1    0  15.9G  0 lvm  [SWAP]
sdb                            8:16   0 238.5G  0 disk 
├─sdb1                         8:17   0   100M  0 part 
└─sdb2                         8:18   0 238.4G  0 part 
sr0                           11:0    1  1024M  0 rom  

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So not sure if this is important or not, but in the GUI for boot-repair, where it lets me change the "OS to boot by default" dropwdown bar it lists Windows as the following:

"Windows (via mapper/ubuntu--vg-root menu)"

Answer 1

I can supply a more step by step way of doing the fix in the linked answer. Big picture, we are going to manually add a Windows entry to grub. Most of this procedure is finding the needed information to do that.

1. Find where the windows bootloader resides by mounting the efi partition, and searching for bootmgfw.efi.

On my system (a 64 bit Win 8.1 / Ubuntu dual boot) the EFI partition is already mounted. If it is not on your system, please comment to that effect, and I will revise the answer.

Find the EFI partition by issuing the command lsblk in a terminal window. On my system it is mounted at /boot/efi on partition sda2

cd to that directory and look around for the file bootmgfw.efi. On my system it was located at /boot/efi/EFI/Microsoft/Boot Seems a bit redundant but whatever.

2. Find the uuid of the drive

in a terminal type sudo blkid and enter your password when prompted. This will list all your drives and their UUIDs. In my case I wanted the one for sda2.

3. add this to /etc/grub.d/40_custom

in a terminal type gksudo gedit /etc/grub.d/40_custom and supply your password

Add this entry to the file. Where it says UUID replace the text UUID with the value of the UUID you obtained in step 2. After the (${root}) replace /efi/Microsoft/Boot/bootmgfw.efi with the path you found in step 1.

menuentry "Windows x86_64 UEFI-GPT" {
    search --fs-uuid --no-floppy --set=root UUID
   chainloader (${root})/efi/Microsoft/Boot/bootmgfw.efi
}

4. and finally run update-grub

Type sudo update-grub into the terminal.

Answer 2

There are 2 possibilities now:

For the record: You have 2 drives (1 with windows which is MBR/NTFS partitioned and 1 with Ubuntu which is GPT/ext3-4 partitioned). You're running under a UEFI Bios and have problems of your UEFI-Grub starting up the MBR-Windows.

Possibilities:

1. You are trying to boot your bios-mode Windows 7 bootloader from UEFI-Grub.
   • This will not work. Since @oldfred pointed out you cant mix boot modes.
   • If you have the file (${root})/efi/Microsoft/Boot/EFIMicrosoftBootbootmgfw.efi) that is NOT your Problem, because MBR or GPT is not important here but Windows wont create a efi boot file if you install it in MBR mode.
   • make a backup of your bootloader partition (sdb1) before the next step (e.g. with clonezilla)
   • If you DONT have this file then windows can create a efi bootloader. Described in this post: How to boot Windows 8 from a legacy MBR partition in UEFI mode via GRUB?

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2. You alread have the efi boot file (e.g. EFIMicrosoftBootbootmgfw.efi)

   • If you already have a Windows efi boot file e.g. (EFIMicrosoftBootbootmgfw.efi) like pointed out in your boot-repair log in line 1301, then try different options in the configuration in your /etc/grub.d/40_custom. For you that would be:

     menuentry "Windows 7 " --class windows --class os {
     insmod part_msdos
     insmod ntfs
     insmod search_fs_uuid
     insmod chain
     
     set root='hd1,msdos1'
     if [ x$feature_platform_search_hint = xy ]; then
       search --no-floppy --fs-uuid --set=root --hint-bios=hd1,msdos1 --hint-efi=hd1,msdos1 --hint-baremetal=ahci1,msdos1  06D67F5BD67F4A47 
     else
       search --no-floppy --fs-uuid --set=root 06D67F5BD67F4A47 
     fi
     
     chainloader (${root})/efi/Microsoft/Boot/EFIMicrosoftBootbootmgfw.efi
     
     }
     

   • These values are read from your boot-repair log or are guessed. If your efi boot file is at a different location change the line chainloader ...

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3. Last but not least you can still wipe your second harddrive. Partition it with GPT/NFTS and then install a new windows. Data loss coming up here