John Austin wrote: > On Mon, 2007-12-31 at 12:33 -0600, Mikkel L. Ellertson wrote: >> What I did was install a copy of Grub to the MBR of the USB drive, >> and then create an entry like this in the SATA Grub menu: >> >> title USB disk >> root (hd0) >> map (hd0) (hd1) >> map (hd1) (hd0) >> chainload +1 >> >> Because of the map commands, the USB drive is hd0 when the chainload >> command is executed, and it loads Grub from the USB drive. (hd0 is >> the entire disk, starting from the MBR.) From there it is the same >> as if you had used the BIOS option to boot from the USB drive. The >> only thing you have to be careful of is if you have more then one >> USB drive plugged in. You will get a Grub error is the wrong one is >> detected first, and does not have a boot loader on it. >> >> Mikkel >> -- > Hi Mikkel > > I liked your way of doing things but when I try on my machine as soon as > I use the map command grub gets in a real muddle. > It is not a problem to me but it should work !!!!!!!!! > > Even simple things from the grub command start failing > > Eg > I can boot into interactive grub from SATA disk > and re enter grub many times as follows > > With SATA=(hd0) USB=(hd1) > (SATA is F8 x86-64, USB is F8 i386) both updated to within 3 days. > Both have /dev/sdx1 = /boot, /dev/sdx2 = /, /dev/sdx3 = swap > > root (hd0) > chainloader +1 > re-enters the SATA grub menu > This is because the SATA drive is still mapped as hd0. The pair of map commands changes that. > root (hd1) > chainloader +1 > enters the USB grub menu > > root (hd1) > chainloader +1 > re-enters the USB grub menu > > root (hd0) > chainloader +1 > re-enters the SATA grub menu > > as soon as I do the following grub falls apart !!!!!!!!!! > root (hd0) > map (hd0) (hd1) > map (hd1) (hd0) > chainloader +1 > > Interesting ? > > John > It sounds like Grub on your USB drive is configured to use hd1, not hd0. The menu entry I gave is for booting from a USB drive that is configured so you can boot off it using the boot from USB option of the BIOS. In that case, the USB drive is hd0, not hd1. That is why you need to remap the drives when booting from the SATA drive, and chaining to the USB copy of Grub. One other note - this will work with any bootable USB drive or memory stick. It does not need to have Grub. It will even work on a bootable DOS memory stick. (DOS uses the BIOS to access the drive.) I don't have a USB floppy or CD-ROM drive to test it on, but I would not expect it to work. On the other hand, Windows in the safe mode may work. (95, 98 and maybe XP. But probably not Vista.) One use would be a "pen" drive with OpenDOS configured for BIOS upgrades. Mikkel -- Do not meddle in the affairs of dragons, for thou art crunchy and taste good with Ketchup!
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