Possible to chainload a extracted CD boot sector ? External links Options

[gbrao]

If I extract the boot sector from a CD ( say cd1bsect.bin ) and then create a g4d bootable DVD with cd1bsect.bin and the contents of the CD at the root of the DVD, can I then chainload cd1bsect.bin from grldr ?

Basically I want to put a number of bootable CDs onto a single DVD. I thought that might be the simplest way. Can I have something like this in the DVD menu.lst :

CODE

title Boot CD1
find --set-root /grldr
chainloader /cd1bsect.bin

title Boot CD2
find --set-root /grldr
chainloader /cd2bsect.bin

.
I would not have to bother where the boot sector from each CD transfers control.

[Wonko the Sane]

Well, the whole idea of the great additional features of grub4dos is that of directly chainloading system files in order to bypass bootsector problems, so it does seem like a strange approach.

But I don't see the problem.

I mean have you tried it and it fails or is this a "preventive" question?

If the latter, just try it, and report what happens.
If the former, report what happens....



Wonko

[gbrao]

Well, my DVD writer is not working. I will burn the DVD at my friends place tomorrow and report.

If you are using a "well-known" CD then directly chainloading system files is fine. For eg., with a Windows XP installation CD. However sometimes it is not so obvious - one of the bootable CDs I have has been created with EZBoot (EasyBoot ?). I could go thru the trouble of finding out where exactly the MBR transfers control, but with the the way I suggested in post 1 I wouldn't have to. That's all.

No one has thought of this / tried this before ?

I've been really unlucky with DVD writers.

[Wonko the Sane]

No one has thought of this / tried this before ?

Sure , it is one of the "traditional" way ISOLINUX can work:
http://syslinux.zytor.com/wiki/index.php/S...NUX#KERNEL_file

Point is that chainloading a bootsector may give different results depending on the actual bootsector content.

I've been really unlucky with DVD writers.

They do have a higher failure rate when compared with CD writers, cannot say because they need more accurate "alighment" or because they have become so cheap.

And we still have to see what will happen with Blue_Ray's.

Well, my DVD writer is not working. I will burn the DVD at my friends place tomorrow and report.

Well, you should be able to create an .iso of the "compilation" and test it in a VM. (if it doesn't work in a VM it doesn't "necessarily" mean it won't work on real hardware, but if it works, usually it will also work on real hardware).



Wonko

[gbrao]

I tried booting a image in QEMU. When chainloading the extracted bootsector I get the error mesg "Error 13: Invalid or unsupported executable format".

[Wonko the Sane]

Good.

So it isn't possible.

Now try using ISOLINUX instead of grub4dos as "main" loader.

And try "chainloading" from it the CD bootsector as a file with extension .BIN.

Wonko

[gbrao]

^ Yes, the ISOLINUX method worked. Thanks.

[Wonko the Sane]

^ Yes, the ISOLINUX method worked. Thanks.

Good.

Why don't you post some details of your working setup, as they might help another user of the board with same or similar problems.



Wonko

[gbrao]

Nothing new really.

1) Created a ISO image using mkisofs as per link . Actually it was :

CODE

pause

mkisofs -r -J -joliet-long -l -allow-lowercase -b isolinux.bin -no-emul-boot -boot-load-size 4 -boot-info-table -o gbootdvd.iso -V GBOOTDVD2010Feb -p gbrao iso_root

pause

I used only one CD since this was just a test. Will do the full compilation today. btw : does mkisofs need filenames like isolinux.bin in (-b isolinux.bin) to be uppercase ? I kept getting "unable to find isolinux.bin" until I uppercased it. Also some checksum error until I included -boot-info-table.

2) the cfg file was pretty basic :

CODE

DEFAULT test
LABEL test
SAY Now booting BS.BIN...
KERNEL BS.BIN

3) I had isolinux.bin & isolinux.cfg in the root of the image. BS.BIN is the CD boot sector.

If this can be corrected/improved, please point it out. I'm very inexperienced.

what's the recommended way to extract the boot sector from a CD ? I tried ultraiso and bbie - they seemed to extract different bootsectors ?! I tried the one from ultraiso.

[Icecube]

Also some checksum error until I included -boot-info-table.

The -boot-info-table option is needed for ISOLINUX. The option patches isolinux.bin, so the 2kb boot sector of ISOLINUX can find the rest of the isolinux.bin file on the CD. ISOLINUX checks the checksum to see if the correct file is loaded.

2) the cfg file was pretty basic :

CODE

DEFAULT test
LABEL test
SAY Now booting BS.BIN...
KERNEL BS.BIN

Note: The SAY command is not specific to a LABEL, so when you have multiple LABELs in your config all SAY messages will be displayed.

Instead of KERNEL (you need extension .bin if you want to boot the file as CD bootsector), you can use BOOT (file extension doesn't need to be .bin).

CODE

DEFAULT test
LABEL test
SAY Now booting BS.BIN...
BOOT BS.BIN

what's the recommended way to extract the boot sector from a CD ? I tried ultraiso and bbie - they seemed to extract different bootsectors ?! I tried the one from ultraiso.

You can open an ISO with 7-zip (which is free). If it is a bootable ISO, 7-zip will display a [BOOT] folder. 7-zip will even tell you what kind of boot sector the CD uses (no-emulation, hard disk emulation or floppy emulation).