Re: Booting from an external drive

[Pascal Hambourg]

Le 09/04/2017 à 20:14, Dale R. Worley a écrit :
> I recently got into a situation where it would have been convenient to
> put a "system" disk for one computer (a disk with Grub boot, a Linux
> image, and the disk partitions) into an external enclosure, plug that
> into a USB drive of another computer, then get that computer to boot
> from the external disk.
>
> This leads me ask these questions.  I hope that the answers are
> well-known.
>
> 1. Once the computer chain-loads the boot from an external disk, I
> assume Grub is smart enough to fetch phases 1.5 and 2 and the boot image
> from wherever it was loaded.

Stages 1.5 and 2 were specific to GRUB legacy (GRUB 1). The current GRUB 
version (GRUB 2) only has a boot image and a core image.

> 2. If grub.cfg on the external disk is written to locate the the
> partition using UUIDs or other location-independent identifiers (as
> opposed to sda1, etc.), Linux can boot up.

Yes.

> 3. Is there a way to write grub.cfg to locate bootable drives attached
> to USB ports, offer them in menuentry's, and chain-load them?
>
> 4. Bonus points:  Is there a way to load a USB stick with Grub and such
> a grup.cfg so that one can boot a computer off of the USB stick, from
> the menu, select an external disk, and get that Grub to chain-load the
> Grub off the external disk?

A major problem for this is that some BIOSes do not expose all USB 
drives but only the one used for booting.