Issue at Hand
You are unable to boot your system, you are stuck on a grub> shell.
You have a dual boot system with Windows and Debian on a single disk.
Disclaimer
You mention running a command to add a Debian entry to your BCD entry involving UEFI. When you installed Debian do you remember installing your Debian system using UEFI?
If you did not setup UEFI it may be faster to reinstall your system following the procedures outlined here and here.
Recovering from GRUB
First off we will need to fix your GRUB entries to be able to boot. I have found this stack exchange post which covers recovering from grub rescue. Following with user DocSalvager, you will need to find the Debian partition containing your /boot
grub> ls
[ Here should be a list of devices and partitions, e.g. (hd0,1) (hd0,2) (etc) ]
You want to look for your Debian partition it could be something like:
grub> ls (hd0,4)/boot
Repeat this for all listed partitions until you find a result that includes something like initrd.img-... vmlinuz-... or even /grub. Once you find a the partition that contains your Debian boot image you will run the following steps:
grub> set root=(hd0,[partition number you found])/boot
grub> insmod linux
grub> linux (hd0,[partition number you found])/boot/vmlinuz-[image name]
grub> initrd (hd0,[partition number you found])/boot/initrd.img-[image name]
grub> boot
Here you should boot into a Debian system, you may need to further repair your system by:
$ cd /boot
$ mv mod/* grub
$ reboot
I will also include this link you can follow those steps to also repair your boot.
Alternative Steps
Here is some steps to take from the Debian Wiki.
Once booted into a Debian system run these:
[ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"
should return "EFI boot on HDD".
mount /dev/sd[Debian boot Partition, e.g. sda4] /boot/efi
apt-get install --reinstall grub-efi
grub-install /dev/sdX \\ X being the disk with your operating systems
update-grub
file /boot/efi/EFI/debian/grubx64.efi \\ Verify that the file exists
efibootmgr --verbose | grep debian \\ Verify nvram entry was created
Now you should be able to reboot and see a grub menu!
Adding a Windows Entry to GRUB 2 Menu
Once booted into your Debian install and not a rescue disk or anything if you see that you are missing Windows from GRUB you will need to follow these steps:
sudo os-prober \\ If you see your Windows Partition then you can run the next step
sudo grub2-mkconfig
sudo update-grub
If os-prober cannot find your Windows partition you will need to mount the Windows file system. Following along with these steps install ntfs-3g and then mount Windows.
mount -t ntfs-3g -o ro /dev/sd[Windows Partition] /media/windows
sudo os-prober
sudo grub2-mkconfig
sudo update-grub
You should see an entry for Windows be added. You can also manually create an entry using your preferred text editor at /etc/grub.d/40_custom.
menuentry "Windows" {
set root='(hd0,1)' \\ Remember that this should be your Windows boot partition.
chainloader +1
}
Conclusion
You will need to repair your boot process in grub. There are several methods that I have outlined and linked to. If this is a fresh install it could be better to install Debian again following the advice on the Wiki.
I will be including a another link regarding booting with GRUB as well as another forum post about a similar issue.
Please comment if you have any questions or issues with this answer. I highly suggest you read through each link I have provided thoroughly before attempting the commands. I appreciate feedback to correct any misconceptions and to improve my posts. I can update my answer as needed.
Best of Luck!
