Booting Grub From CD

[Leo]

I recently installed Slackware on a pc with windows and did not want to write over the Master Boot Record (MBR) or so needed an alternative way to boot into Linux. Since the machine did not have a floppy drive a floppy bootdisk was not the answer and I want to bugger about with the kernel so using the install cd was not an option either as it would use the kernel image on the disk.

 

I wanted to install a boot loader onto a CD that I could boot from and which would allow me to select the kernel from the hard disk.

 

After Googling for a bit (alright, bloody ages!) I came across LinuxQuestions.org

Which all but answered my questions. So here is what I did (the vast majority of the code and method comes from homey at linuxquestions.org)

 

This was all done on a second machine that has a floppy drive, cd writer and boots Linux (Mandrake 9.0) using Grub.

 

First (as root) I copied the existing /boot/grub/menu.lst to a temporary file.

#cp /boot/grub/menu.lst /boot/grub/menu.lst.copy

next using vi I amended menu.lst to add an option boot my Slackware partition as though it were on the current machine (it exists on hda3 on the other machine)

title linux
kernel (hd0,2)/boot/vmlinuz root=/dev/hda3 devfs=mount hdc=ide-scsi

having saved the changes I then formatted a floppy and created a /boot/grub directory on it before copying my existing /boot/grub directory contents into it.

#fdformat /dev/fd0
#mke2fs -m 0 /dev/fd0
#mount -t ext2 /dev/fd0 /mnt/floppy
#mkdir -p /mnt/floppy/boot/grub
#cp -pa /boot/grub/* /mnt/floppy/boot/grub
#umount /mnt/floppy

Next I created a text file /home/stuff using vi

#vi /home/stuff

and wrote the following grub install script into it:

root (fd0)
#the following is all on one line
install /boot/grub/stage1 d (fd0) (fd0)/boot/grub/stage2 0x8000 p (fd0)/boot/grb/menu.lst
#
quit

The next step was to install grub onto the floppy disk using:

#grep -v ^# /home/stuff | grub --batch

this ran the install script by ignoring any line beginning with a #

This gave me a floppy bootdisk.

I now copied the contents of the bootdisk into a file boot.img

#dd if=/dev/fd0 of=boot.img bs=10k count=144

and created an iso image using the boot.img file and using the El-Torrito option (-r) that let me make my cd look like a bootable floppy to the bios. I also had to specify the pathname of the boot.img

#mkisofs -r -b boot.img -o bootcd.iso /home

I was then able to create the bootable cd by copying the iso image to a cd(remembering to get the correct device using cdrecord -scanbus):

#cdrecord -v speed=4 dev=0,2,0 -data bootcd.iso

Finally I replace the amended version of /boot/grub/menu.lst with my original (no really, I did, I didn't forget and try rebooting my machine with the wrong version in it ):

#cp -f /boot/grub/menu.lst.copy /boot/grub/menu.lst

I was then able to boot my pc with the Slackware distro using the cd so now when it boots I get presented with the Grub loader screen.

 

If you have any suggestions for improvements to this please feel free to add them. And once again I would like to make clear that the vast majority of this is transposed almost verbatim from a reply by homey on LinuxQuestions .org (linked).

 

Leo