GRUB Boot Loader

You would have come across GRUB bootloader in case if your are working on Linux systems. I first came accross this when i tried to install my favourite Debian

Load Windows from GRUB

https://unix.stackexchange.com/questions/259069/how-to-start-a-windows-partition-from-the-grub-command-line

set root=(hd0,gpt1)
chainloader /EFI/Microsoft/Boot/bootmgfw.efi
boot

Load Debian from GRUB

https://superuser.com/questions/1237684/how-to-boot-from-grub-shell

grub> set root=(hd0,1)
grub> linux /boot/vmlinuz-3.13.0-29-generic root=/dev/sda1
grub> initrd /boot/initrd.img-3.13.0-29-generic
grub> boot


On some Linux systems the current kernels and initrds are symlinked into the top level of the root filesystem:
https://www.linuxfoundation.org/blog/blog/classic-sysadmin-how-to-rescue-a-non-booting-grub-2-on-linux


$ ls -l /
vmlinuz -> boot/vmlinuz-3.13.0-29-generic
initrd.img -> boot/initrd.img-3.13.0-29-generic
So you could boot from grub> like this:

grub> set root=(hd0,1)
grub> linux /vmlinuz root=/dev/sda1
grub> initrd /initrd.img
grub> boot

Frequently Used GRUB Commands

grub> ls
(hd0) (hd0,msdos2) (hd0,msdos1)

grub> ls (hd0,1)/
lost+found/ bin/ boot/ cdrom/ dev/ etc/ home/  lib/
lib64/ media/ mnt/ opt/ proc/ root/ run/ sbin/ 
srv/ sys/ tmp/ usr/ var/ vmlinuz vmlinuz.old
initrd.img initrd.img.old

grub> cat (hd0,1)/etc/issue
Ubuntu 14.04 LTS n l

References

https://www.redswitches.com/blog/grub-rescue-commands

Troubleshooting GRUB Loading.

https://www.linuxfoundation.org/blog/blog/classic-sysadmin-how-to-rescue-a-non-booting-grub-2-on-linux

How to enable dual boot in windows

https://www.makeuseof.com/windows-10-dual-boot-option-not-showing