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Bootable El-Torito CD with GRUB Legacy: Difference between revisions
Bootable El-Torito CD with GRUB Legacy (view source)
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You will need the following:
* [[mkisofs]], which is in fact superseeded by [[genisoimage]].
* A (Multiboot compliant) kernel that [[GRUB Legacy]] can boot.
* The El-Torito GRUB Legacy stage2 file, called <tt>stage2_eltorito</tt>.
=== Ubuntu/Debian ===
In Ubuntu or Debian you can install the required software like this:
<syntaxhighlight lang="bash">
sudo apt-get install genisoimage grub
</syntaxhighlight>
We need a place to store the files on the CD image:
<syntaxhighlight lang="bash">
cd # Go to your home directory.
mkdir -p isofiles/boot/grub
</syntaxhighlight>
You now created an <tt>isofiles</tt> directory in your home folder and a <tt>boot/grub</tt> sub-folder inside that. We need the stage2 file. It is installed from the grub package. Just copy it:
<syntaxhighlight lang="bash">
cp /usr/lib/grub/i386-pc/stage2_eltorito ~/isofiles/boot/grub/
</syntaxhighlight>
=== Windows ===
Look at [[mkisofs#Under windows|this article about how to install and use mkisofs]]. We need a place to store the files on the CD image. Create a folder <tt>isofiles</tt>, which contains the sub-folder <tt>boot\grub</tt> needed by GRUB. We need the stage2 file. You can get it by [http://www.geocities.com/imulgrew/grub_files.tar.gz downloading a package] and unpack it using your favourite
== Install a kernel ==
Get a kernel of your own choosing and copy it to wherever you like inside the <tt>isofiles</tt> folder. Preferably it should be placed in the <tt>boot</tt> sub-folder. Now create a <tt>menu.lst</tt> file. This file controls what menu entries GRUB should provide and how the kernels are booted. It must be placed in the GRUB folder <tt>boot/grub</tt> and contain something like this:
<!-- Not really Bash, it's Grub scripting, but lang="bash" makes nice syntax highlighting. -->
<syntaxhighlight lang="bash">
default 0
#timeout 30
#title Boot from hard disk
#chainloader (hd0)+1
title My kernel
kernel /boot/kernel-file # Edit it to the filename of your kernel.
</syntaxhighlight>
In GRUB there's a concept called root. It's the disk drive or partition where you access the files, like the kernel image and modules. When booting from CD using <tt>stage2_eltorito</tt> you don't need to set the root as it is already set to "<tt>(cd)</tt>".
== Create the .iso image ==
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In the following I use the command <tt>genisoimage</tt>, but you can change it to <tt>mkisofs</tt> if that is what its called on your system. Open a command prompt/terminal and go to where the <tt>isofiles</tt> folder is located. It is your home directory on Ubuntu. Issue the command:
<syntaxhighlight lang="bash">
genisoimage -R -b boot/grub/stage2_eltorito -no-emul-boot -boot-load-size 4
-boot-info-table -o bootable.iso isofiles
</syntaxhighlight>
Now you have a file called <tt>bootable.iso</tt>. Test it using your favourite emulator or burn it to a CD and test on a real computer. I will just explain the command line arguments we used for genisoimage:
{| {{Wikitable}}
|-
| -R
| Use the Rock Ridge protocol, which enables lower-case filenames on the CD. This is needed by GRUB.
|-
| -b ''file''
| The file to boot (the filename is in the created [[ISO 9660]] file system).
|-
| -no-emul-boot
| Enables no emulation El-Torito boot.
|-
| -boot-load-size 4
| Specifies the number of 512-bytes sectors to load. Four 512-byte sectors (2048 bytes) is one CD sector and is the number supported by most BIOS.
|-
| -boot-info-table
| Patches the boot file to contain info about the CD image. It's needed by GRUB.
|-
| -o bootable.iso
| The filename of the resulting .iso image.
|-
| isofiles
| Other arguments are the files and folders that should be included on the CD. In this case it's only the content of ''isofiles''.
|}
== Advanced stuff ==
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=== Give it a label ===
You want to label your CD image, so you can later recognize it when loading your CD. Just pass a '''-
=== Make it be quiet ===
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=== Make the image from different files and folders ===
When you are building your kernel the parts on the .iso image could be located at different paths.
<!-- Fancy Unicode/ascii art tree. Created in Ubuntu command line: "tree -A -F --dirsfirst" -->
<pre>
project/
├── build/
│ ├── modules/
│ │ ├── iso9660.mod
│ │ └── kbdrv.mod
│ └── my-kernel.elf
├── src/
│ ├── grub/
│ │ └── menu.lst
│ └── ...
├── thirdparty/
│ └── grub/
│ └── stage2_eltorito
└── Makefile
</pre>
You don't want to copy those files around in order to create the .iso image. Just use the '''-graft-points''' argument, like this:
<syntaxhighlight lang="bash">
genisoimage -graft-points # ...other arguments here...
modules/=build/modules/
</syntaxhighlight>
You can use both files and folders together with the -graft-points argument.
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If you don't find a solution to your problem below, please ask in [http://forum.osdev.org/ the forums].
=== mkisofs says Uh oh, I
The output of mkisofs looks like this:
<pre>
mkisofs: Uh oh, I cant find the boot image 'isofiles/boot/grub/stage2_eltorito' !
</pre>
This problem arises because mkisofs/genisoimage looks for its boot image as a subdirectory of the filesystem on the CD; make sure that the path you specify starts with 'boot/' rather than the name of your ISO directory ('isofiles/' in this example).
Source: [[topic:20102|this thread]]
=== I get a permission denied error in Linux ===
The output of genisoimage looks like this:
<pre>
Size of boot image is 4 sectors -> No emulation
genisoimage: Permission denied. Error opening boot image file 'isofiles/boot/grub/stage2_eltorito' for update.
</pre>
The problem is that
<syntaxhighlight lang="bash">
chown myself isofiles/boot/grub/stage2_eltorito # Make sure you are the owner of the file. Replace "myself"
# with your username. Maybe you need to use sudo.
chmod u+w isofiles/boot/grub/stage2_eltorito # Make the file writable for the owner of the file (you).
</syntaxhighlight>
== See Also ==
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* [[mkisofs]]
* [[Bootable CD]] - using floppy disk emulation
* [[GRUB]] - for info on using GRUB 2 to make a bootable CD with modern GRUB
=== Forum ===
* [[topic:19050|Thread about making your own .iso image from scratch without tools]]
=== External Links ===
* [http://www.geocities.com/imulgrew/grub_files.tar.gz Package containing the GRUB stages] (including <tt>stage2_eltorito</tt>)
* [ftp://alpha.gnu.org/gnu/grub/grub-0.97.tar.gz Source for GRUB Legacy] to build it yourself
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[[Category:Tutorials]]
[[Category:Bootloaders]]
[[Category:GRUB]]
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