In the grub bootloader if you press esc it will take you to a command line interface that looks like
What is this promt used for? It doesn't look like it's connected to Linux. Is it a command shell provided by the bootloader?
Yes, it is provided by GRUB. The GRUB command shell is just as powerful as the shell. You can use it to discover boot images, kernels, and root filesystems. When you're at the grub> prompt, you have a lot of functionality similar to any command shell such as history and tab-completion. The grub rescue> mode is more limited, with no history and no tab-completion.
You can get lot of inputs in here
GRUB provides following interface:
From GRUB’s user interface:
Note: you can run