booting from DVD image on hard drive partition

[stan]

On Thu, 29 Mar 2012 12:16:11 -0500 (CDT)
Michael Hennebry <hennebry at web.cs.ndsu.nodak.edu> wrote:

> On Thu, 29 Mar 2012, stan wrote:
> 
> > On Wed, 28 Mar 2012 23:33:49 -0500 (CDT)
> > Michael Hennebry <hennebry at web.cs.ndsu.nodak.edu> wrote:
> >
> >> Since /boot and / are on disk sdb, I'd like the bootloader there
> >> also. Frustration is bad for my brain.  Ignore my previous request
> >> on this subject. I know how to change the boot hard disk in my
> >> BIOS. What else do I need to do?
> >
> > You need to install the mbr on sdb.  Then change your BIOS to make
> > it
> 
> I've tried to do this before.
> The best result was a grub command line on boot.

Then something isn't right.  I have several disks with mbrs on them,
and when I switch to them, they boot.  As I said below, I'm rusty
because everything has just worked for so long.  I vaguely recall
running a map command in grub so it enumerated the disks as it saw
them.  And installing the various stages, I think.

> > the first boot disk, and you will boot sdb. 
> >
> >> Is it written in TFM somewhere?
> >
> > F15 still uses legacy grub as default.  So, you can boot a rescue CD
> > and install grub to the mbr on sdb, or boot onto sda, umount sdb,
> > and use grub directly on the unmounted disk (I think I've seen this
> > in the
> 
> "Use grub" is not all that helpful.  I really need more detail.
> TFM has not been my friend.

It's been years since I actually had to install an mbr.  Perhaps
someone else will have done it recently, but I would have to do
research and experimentation in order to tell you what to do.  Even
then that would be on my system, not yours, and so might be
inapplicable (your system seems to have many 'gotchas').

> It's not even clear to me why I would need to unmount the disk.
> I expect that unmounting the disk means to unmount all its partitions.

Maybe you don't;  it is probably my excessive addiction to prevention
of problems.  Umounted disks have no read write activity to interfere
with the grub mbr write process.  It shouldn't matter, and in fact
grub2 seems to explicitly allow this on mounted disks, but I'm erring
on the side of caution.  Hey, breaking things and then fixing them
is a great way to learn, but I'll pass.