[lug] "boot floppy" CD creation recommendations

[D. Stimits]

Bear Giles wrote:

> I'm trying to figure out how to create a "boot floppy" CD.  By that I 
> mean a 1.44MB image that I can put into the 'el Torino' boot sector 
> and boot straight to the HD, same as the floppy rescue disk.
>
> If the system had a floppy drive.
>
> I don't want/need something like 'knoppix' since this should be 
> entirely automatic and can be keyed to this specific system.  I 
> remember using syslinux to create the current boot CD two years ago, 
> but I also remember that process as being painful and creating a high 
> stack of coasters.
>
> I have grub on the system, so getting to it should be enough.  I don't 
> know if I can do that via syslinux.
>
> Ideas?
>
> (Why go to this bother?  The bios on this 'server grade hardware', 
> probably to drive their own $$$ hard drives, does not recognize IDE 
> drives as bootable disks. )


I never tried this, but it would be a cheap and easy test...put a floppy 
in the drive, , and do a grub-install to the floppy which points at the 
grub partition. Then create a file from the floppy via:
dd if=/dev/fd0 of=/tmp/testboot.iso bs=512

Use that file if it boots correctly from the floppy. My main concern is 
that the BIOS will argue if the image used does not cleanly fit in its 
idea of a floppy, e.g., if your BIOS can't support a 2.88 MB floppy 
(perhaps because it requires one to actually be installed), then it'll 
reject the image. I doubt it will reject a small image, it definitely 
won't work with an image which is too large.

YMMV, have not tried it. However, you don't really need a 1.44 MB image, 
though you could tell dd to pad the iso it creates such that it is 1.44 
MB. Theory is that the actual boot sector is a 512 byte block, that 
anything beyond this is used for things like initrd files. If you don't 
have other requirements, it *might* be possible to to get by with 
nothing more than that single block. FYI, you can backup and restore a 
MBR or PBR this way as well (which I have done). If it doesn't work, it 
was an easy test. If you happen to have a working boot sector on any 
hard drive, you could skip installing to a floppy and read directly off 
of that drive (the dd command above does not write anything to the boot 
sector, it writes strictly to the /tmp/testboot.is).

D. Stimits, stimits AT comcast DOT net