What would it take for a *nix system to shutdown, then continue to grub?

Question

Is this possible to shutdown to grub, not all the way so you don't have to load back up the BIOS and other things. Like to give you the ability to quickly boot for Linux to Windows?

Answer 1

The only similar utility I'm aware of is Kexec. Sadly, it can only boot a new Linux Kernel from within Linux (useful for Kernel updates without resetting the hardware.) As far as I know, doing the same for Windows or using such for fast switching between *nix and Windows is not possible with Kexec.

Answer 2

No you can't

When Grub boots a kernel, it eventually hands over control to it, it doesn't stay in a dormant state or something.

Think of Grub as a tiny OS. When you boot a kernel, or chainload into a device, GRUB is gone. The only similar thing to achieve, would be using something like EFI, but that actually starts when an OS turns over control to whatever else. On VAXstations, it was possible to halt the system and break into a prompt called chevron (">>>"). You could make basic hardware checks, etc in there, but also format harddrives. Afterwards, the OS could be freed from its frozen state again, and was running from the previously halted point as if nothing had happened.