grub: breaking the 1gb barrier

Forum: USB booting
Topic: grub: breaking the 1gb barrier
started by: ~thc

Posted by ~thc on Feb. 21 2007,20:26
use extreme caution: several steps mentioned below could ruin your pendrive and/or your harddisk
DO NOT COPY AND PASTE COMMANDS - double check what you are doing!
I have tested this with a 2 gb pendrive (fat16) / knoppix 5.1.1 and a 512 mb pendrive (fat32) / dsl 2.1.

the filenames, directoriy names and grub settings used below are only examples!

what you need

- an usb pendrive of any size formatted as a hard disk
- the first or only partition of this pendrive formatted with a fat filesystem and enough space left for dsl/knoppix
- the contents of a dsl (or other knoppix based) cd
- a real or virtual computer running a linux installation with grub and usb pendrive support
- a pc bios capable of emulating a hard disk booting mechanism for the usb pendrive

step by step

1. copy the following dsl/knoppix files to the usb pendrive

(cd)/boot/isolinux/kernel_filename -> (usb)/boot/linux
(cd)/boot/isolinux/gzipped_miniroot_filename -> (usb)/boot/minirt.gz

[starting with knoppix 5 the cd contains essential kernel modules in /KNOPPIX/modules - you will need this directory and all files in it too.]

2. convert isolinux.cfg from the dsl/knoppix cd

create a new text file (dos or un*x) namend menu.lst and add those three lines:

Code Sample
default 0
timeout 5
color cyan/blue white/blue

the syntax of the boot entries in (cd)/boot/isolinux/isolinux.cfg and grub's menu.lst differ slightly.

for every dsl/knoppix isolinux.cfg boot entry like this example

Code Sample
LABEL  example
KERNEL linux24
APPEND ramdisk_size=100000 init=/etc/init lang=us apm=power-off vga=791 initrd=minirt24.gz quiet BOOT_IMAGE=knoppix

add the corresponding boot entry to menu.lst like this converted example:

Code Sample
title  example
kernel /boot/linux ramdisk_size=100000 init=/etc/init lang=us apm=power-off vga=791 quiet BOOT_IMAGE=knoppix
initrd /boot/minirt.gz

another example: a menu.lst file containing only the default dsl 2.1 entry would look like this:

Code Sample
default 0
timeout 5
color cyan/blue white/blue

title dsl
kernel /boot/linux ramdisk_size=100000 init=/etc/init lang=us apm=power-off vga=791 nomce noapic quiet BOOT_IMAGE=knoppix
initrd /boot/minirt.gz

create a directory (usb)/boot/grub.
copy the file menu.lst to (usb)/boot/grub

3. prepare the grub install

boot the linux installation and mount your usb pendrive (sda1 and /mnt are only examples!)

Code Sample
# mount /dev/sda1 /mnt

copy the grub stage loader files from the linux installation to the stick

Code Sample
# cp /boot/grub/stage1 /mnt/boot/grub
# cp /boot/grub/fat_stage1_5 /mnt/boot/grub
# cp /boot/grub/stage2 /mnt/boot/grub

mark the usb grub directory by putting a unique file there:

Code Sample
# touch /mnt/boot/grub/mark

4. install grub

start grub from the command line.

Code Sample
# grub

from the grub shell enter the following commands (hd1 and the grub output are only examples!):

Code Sample
grub> find /boot/grub/mark

grub> root (hd1,0)
 Filesystem type is fat, partition type 0xe

grub> setup (hd1)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/fat_stage1_5" exists... yes
 Running "embed /boot/grub/fat_stage1_5 (hd1)"...  15 sectors are embedded.
 Runnung "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2
/boot/grub/menu.lst"... succeeded

grub> quit

the file "mark" is no longer needed:

Code Sample
# rm /mnt/boot/grub/mark
# umount /mnt

the stick should now boot into grub.


- grub's stage 1.5 loader reads file systems, not hard disk sectors - you don't have to worry about the geometry or the size of your pendrive.

- grub's setup does not alter neither the boot sector of the first (or only) pendrive partition nor the contents of that partition.
[the stage 1.5 loader is written to 15 (normally empty and unused) sectors directly following the mbr/partition table.]

- if bartpe is (or will be ;) ) installed on your pendrive, you can tell grub to boot it by adding to menu.lst:

Code Sample
title bartpe
chainloader +1

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