Booting a USB from the Grub command prompt

Question

I have a USB drive that I know is bootable (tested it on a different PC), but because of an ancient BIOS, I am unable to set it as a boot device in the BIOS settings.

The computer I am using has GRUB 0.97 installed, and I was thinking: Surely it must be possible to tell grub to just boot from said USB instead? If so, the questions are:

After loading the GRUB prompt (by hitting C in the bootloader selection), how do I see available devices to boot from? I have no idea what the USB registers as.

Note: Yes, the computer can read the USB fine once an OS is booted. Hopefully Grub is sophisticated enough to be able to do so as well

Solution

To search for your USB drive, use the root command to choose a drive/partition and the find command to see if you found the right one.

You can go through your devices like in this example:

grub> root (hd0,0)   # first harddrive, first partition
grub> find /[tab]    # type the slash then press [tab], and it will try to list files on this partition
Error 17: Cannot mount selected partition   # Oops no file system here
grub> root (hd0,1)   # first harddrive, second partition
grub> find /[tab]
    Possible files are: lost+found var etc media ...   # That was my hard drive with my linux install
grub> root (hd1,0)   # second hard drive usually is the USB drive if you have only one internal drive
grub> find /[tab]
    Possible files are: ldlinux.sys mydoc myfile mystick syslinux.cfg  # Bingo, that's the USB stick
    Note: If you have two internal drives including your CD/DVD drive, the USB drive probably is hd2,0 and so on.

Boot the drive by entering:

chainloader +1
boot

For convenience, add these commands to your GRUB configuration (usually in /boot/grub/menu.lst):

# to boot from a USB device
title    Boot USB drive
root     (hd1,0)
chainloader +1
boot

Source: BootFromUSB - ubuntu documentation

Comments

[Jarmund]

Cheers for a well written and detailed response! Will test tomorrow.

[Wayfarer]

@Jarmund Kudos should go to the Ubuntu Documentation community; I've just copied the content from there, changed some verbal forms and reformatted to fit the styles here :-)

[DavidPostill]

Please do not post the same answer to multiple questions. If the same information really answers both questions, then one question (usually the newer one) should be closed as a duplicate of the other. You can indicate this by voting to close it as a duplicate or, if you don't have enough reputation for that, raise a flag to indicate that it's a duplicate. Otherwise tailor your answer to this question and don't just paste the same answer in multiple places.