How to add windows 10 to grub

Windows 10 will, for the most part, be added to grub boot menu by the os-prober automajically.

For my specific setup I wanted to completely hide grub menu and automatically boot windows unless a hotkey was pressed to boot Ubuntu. So in my specific case os-prober isn’t an option because the most important step in hiding the grub menu, which most answers I found neglect to mention, is to set the disable os-prober flag or the menu WILL be shown until os-prober completes.

It took considerably longer than I had anticipated to get right because there are so many partial answers out there but most are version dependant and can lead you astray. I spent a lot of time trying write my own grub menu entry trying use grub commands that didn’t exist like ntdlr. Another caveat is that the chainloader functions on my grub try to boot bios not efi and will not work.(Im sure I was doing something wrong?)

In the end the solution was actually simple as the scripts that make your /boot/grub/grub.cfg do most of the work for you in finding UUIDS for your boot partitions. So you can skip the fdisk and blkid steps most people mention.

So step 1 is to make sure /boot/grub/grub.cfg is current using update-grub to make .cfg file. In terminal

sudo update-grub

Step 2 is to add custom menu entries in /etc/grub.d/40_custom. Don’t waste time trying to write your own simply open /boot/grub/grub.cfg search «menuentry» and copy the automatically generated entries.

The first in the list will be ubuntu mine looks like

menuentry 'Ubuntu' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-9e66eed6-e672-49ff-a07c-afdc00809148' {
recordfail
load_video
gfxmode $linux_gfx_mode
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_gpt
insmod ext2
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root  9e66eed6-e672-49ff-a07c-afdc00809148
else
  search --no-floppy --fs-uuid --set=root 9e66eed6-e672-49ff-a07c-afdc00809148
fi
linux   /boot/vmlinuz-5.4.0-39-generic root=UUID=9e66eed6-e672-49ff-a07c-afdc00809148 ro  quiet splash $vt_handoff
initrd  /boot/initrd.img-5.4.0-39-generic

}

Windows will be similar. Copy both to /etc/grub.d/40_custom. The only change I made for Ubuntu is to add the —hotkey=key flag which will make grub boot the os associated with that hotkey.

menuentry 'Ubuntu2' --class ubuntu --class gnu-linux --class gnu --class os --hotkey=u $menuentry_id_option 'gnulinux-simple-9e66eed6-e672-49ff-a07c-afdc00809148' {
recordfail
load_video
gfxmode $linux_gfx_mode
insmod gzio
if [ x$grub_platform = xxen ]; then insmod xzio; insmod lzopio; fi
insmod part_gpt
insmod ext2
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root  9e66eed6-e672-49ff-a07c-afdc00809148
else
  search --no-floppy --fs-uuid --set=root 9e66eed6-e672-49ff-a07c-afdc00809148
fi
linux   /boot/vmlinuz-5.4.0-39-generic root=UUID=9e66eed6-e672-49ff-a07c-afdc00809148 ro  quiet splash $vt_handoff
initrd  /boot/initrd.img-5.4.0-39-generic

}

I use —hotkey=u here to set Ubuntu boot hotkey to u.

Then I tweaked the Windows entry, replacing $menuentry_id_option withe the grub —id flag.

menuentry "Windows 10" --class windows --class os --id windows-custom {
insmod part_gpt
insmod fat
if [ x$feature_platform_search_hint = xy ]; then
  search --no-floppy --fs-uuid --set=root  0EAE-C882
else
  search --no-floppy --fs-uuid --set=root 0EAE-C882
fi
chainloader /EFI/Microsoft/Boot/bootmgfw.efi

}

I used —id windows-custom. Save chages to /etc/grub.d/40_custom.

Finally open /etc/default/grub and add

GRUB_DISABLE_OS_PROBER=true

change GRUB_DEFAULT=0 to GRUB_DEFAULT=windows-custom
and change GRUB_TIMEOUT=10 to your choice of timings I use 0.5 just to give myself a little extra time to hit u to boot Ubuntu after POST.

Hopefully this saves someone a bit of headache, cheers!

1. I have installed Windows 10
2. I have installed Linux Mint Silvia and I have chosen a device for boot loader installation — sda.
3. There is not Windows 10 in grub menu when the system starts
4. I have booted via Linux Mint live USB.
5. I Do step by step https://howtoubuntu.org/how-to-repair-restore-reinstall-grub-2-with-a-ubuntu-live-cd
6. But it still no Windows 10 in grub menu
7. I have booted via live windows 10 USB.
8. With restoration tools, I have chosen the command line
9. I have fixed Mbr by console command bootrec /FixMbr
10. Ok, windows 10 is loading by there is no Grub.
11. I have repeated steps 4 and 5
12. There is no result

Also, I have tried to change grub config with this answer
https://askubuntu.com/questions/661947/add-windows-10-to-grub-os-list#answer-977251 — But in this case, There is Windows 10 — but when I chose — I will recursively going to grub

And with this answer
https://askubuntu.com/questions/661947/add-windows-10-to-grub-os-list#answer-890562
I have an error message when chose Windows 10 — There is no bootmgr directory

Thanks @Kinnectus for help

Also, I have tried

sudo os-prober

And getting

/dev/sda1:FreeDOS:FreeDOS:chain
/dev/sda2:FreeDOS:FreeDOS1:chain

And then I have tried

sudo update-grub

And getting

Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.10.0-38-generic
Found initrd image: /boot/initrd.img-4.10.0-38-generic
Found memtest86+ image: /boot/memtest86+.elf
Found memtest86+ image: /boot/memtest86+.bin
Found FreeDOS on /dev/sda1
Found FreeDOS on /dev/sda2
done

Unfortunately — there is not Windows 10 in grub menu

Also, I have fdisk output.

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1            2048  16779263  16777216     8G  c W95 FAT32 (LBA)
/dev/sda2  *     16779264  33556479  16777216     8G  c W95 FAT32 (LBA)
/dev/sda3        33556480 770219115 736662636 351,3G  7 HPFS/NTFS/exFAT
/dev/sda4       770220030 976771071 206551042  98,5G  5 Extended
/dev/sda5       770220032 976771071 206551040  98,5G 83 Linux

Partition 4 does not start on physical sector boundary.

There is an issue.
Maybe the problem is with this issue?

Please, help me, I am stucking with this a whole day.
I completely have no idea, what am I doing wrong.

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