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...making Linux just a little more fun!
Making a Multiple-Boot CD
By Juraj Sipos

I noticed that the issue of making a multiboot CD is not very much covered on the Internet, and if so, only sparsely. Commercial Windows vendors include some possibility to create  bootable CD's in their software, but I haven't yet seen an option to create a multiboot CD in their packages. For me creating a bootable CD in Linux is much easier than in Windows. There are also many free utilities that help you create a Linux bootable CD, but having a multiple boot CD is a delicacy. You can have several versions of Linux boot images on the CD - versions with support for journaling file systems, repair utilities, various breeds of Linux or BSD, or even QNX, Plan9 and more.

Why do I thing this may be good for you? Imagine you use Linux and FreeBSD simultaneously, you have more Linux distributions installed on your hard disk, but something happened to your system - there is no way to access the data anymore. Either you use a bootable diskette (but there may be many obstacles if you work with a specific system like XFS journaling file system, for example, or encrypted files system, and you find that you must have at least 5 Linux bootable diskettes to suit you), or you create a multiboot CD on which you put various breeds of Linux kernels and utilities. A little CD with 10 operating systems on it is redemption from the illusion of this world that makes you believe that something is always wrong.

I want this article to be easy, practical and intelligible for beginners, too, and I'd like to avoid too technical language that is not understood by many of us. This will help attract readers of various sort.

A bootable CD is based upon the so-called El Torrito standard - but there are other sites that explain this. Visit, for example, http://www.cdpage.com/Compact_Disc_Variations/danaboot.html

An important information for us will be that we may have up to 10 bootable operating systems on a CD that we may boot anywhere where the boot ability is supported by BIOS. The bootable ISO image file may be created with 1.44MB diskette emulation, 2.88MB diskette emulation, or hard disk emulation. 

Now follows the practical guide on how to prepare a multiboot CD

First, you must have a bootable DOS or Linux diskette image file. An image is a file that contains the contents of a disk or diskette. There may be many types of image files - if you dd (disk dump) your Linux partition with a command (let's suppose that your Linux partition is on the /dev/hda1 partition): 

dd if=/dev/hda1 of=/my_image.file

a file my_image.file will appear in your file system. Not every image file is bootable - it depends on its contents, so a good idea would be to prepare some Linux or BSD diskette image files. The simplest way would be to download such image files from the Internet. Here is the link:


The Ibiblio archive is very good. The image files you may download from the above URL are prepared in such a way that they are bootable, so you don't need to care much about building your own image. However, if you want to make your own image, at the above URL you may also find some utilities like Bootkit, CatRescue, SAR, disc-recovery-utils, etc., which will help you create your own bootable diskettes (or bootable image files).

The files we will need for our work, in order to make a multiboot CD, are fbsd-flp-1.0.3.bin (a bootable FreeBSD 2.8 MB diskette image), tomsrtbt, or you may create your own images from the diskettes you already have. Put your DOS or Linux diskette in the diskette drive and type the following command:

dd if=/dev/fd0 of=boot.img bs=512 count=2880

A good idea would also be to visit http://freshmeat.net and search for a keyword "mini", so you will find even some esoteric mini Linux distributions you normally don't hear about.

The site http://www.ibiblio.org/pub/Linux/system/recovery/ contains (I deleted some stuff):

Some other good sites where you can download bootable diskette images:

LIAP (http://www.liap.eu.org/): LIAP is a Linux in a Pill - the site contains many 1.44MB diskette images with various utilities and kernel breeds suitable for recovery of various types of disasters.

LEKA RESCUE FLOPPY (http://leka.muumilaakso.org/): Leka Rescue Floppy is a small 1.44Mb distribution.

TOMSRTBT (http://www.toms.net/rb/): Tomsrtbt (Tom's Root Boot) is a rescue utility, a very good one. You may also download the 2.88MB image file from the above site.

You can also download bootable DOS images. Visit, for example, http://www.bootdisk.com and download DOS images if you do not have them available. The site contains DOS 5.00 to 6.22, Win 95/98/Me Bootdisks, DOS/Windows 9X/2000/XP bootdisks, Win 95/98/ME - NT4/NT5 bootdisks, DrDOS 7.X disk for Bios Flashing Basic, etc. You may also create a FreeDOS boot diskette.

First, some terms. Let's see a difference between a bootable image file of a diskette or disk and an ISO image file to be burned on a CD. What we must have are bootable diskette image files from which we will create one ISO image file.

1) You may prepare your bootable diskette images from diskettes you already have with the command:

dd if=/dev/fd0 of=/my_image.img

or you may download some bootable diskette image files from the Internet (see the links). Make a directory in your Linux box, for example - /CD, and copy the images to this directory (remember, you may have not more than ten bootable images). Make sure you keep the 8.3 format for file names - 8 characters for the file name and 3 characters for its suffix - this maximum is only for the compatibility issue with the DOS makebt.exe program we will later use).

2) If you want to make use of the space on the CD (ten images of bootable diskettes would only require about 14MB), place some other utilities in a subdirectory, for example, /CD/Soft. An information how to access the CD is included at the bottom of this article.

3) Run the following command from the /CD directory:

mkisofs -b image.img -c boot.cat -J -l -R -r -o /cd.iso /CD

The "boot.cat" or "boot.catalog" file will be automatically created, so you don't have to have it in your /CD directory - just type the command as you see it - you can type the name of any image file, as long as its name corresponds with the names of image files placed in the /CD directory. The image file included in the above command will be the one you will boot your CD from. The image files must have the size of 1.44MB or 2.8MB.

4) A cd.iso file will be created in your / directory (/cd.iso). When you check this file and mount it (mount /cd.iso /mnt -o loop), the contents of the ISO file should be seen in the directory where you mounted it. This ISO image, if we burn the CD with it, will be bootable but only one image to boot from will be available.

5) So we must edit the ISO image to make a multiple boot CD, thus we will get other images to be included in the menu (0, 1, 2, 3, etc.) we will see when we boot the CD (we will be welcomed by a multiple boot menu with options for 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. By pressing the chosen number we will boot the desirable operating system.

6) After editing it, we may now burn the CD.

Since I don't have the time and effort to create a Perl script that would edit the ISO image for me and because the editing of the ISO image file may appear complicated for some (I want this article to be as simple as possible), it would be a good idea to use some free programs available on the Internet. One of such free programs is makebt.exe. Some time ago, I found this free program on some sites, but now I was unlucky to find it on the net, so I put it on my website http://www.tankred.sk/~juro/freebsd/makebt.zip where you can download it from.

You may run makebt.exe in DOSEMU, BOCHS emulator (http://bochs.sourceforge.net), or you can download DOS system diskette images available at http://www.bootdisk.com, or make a FreeDOS bootable diskette and boot your PC with it in order to run the makebt.exe utility. If you don't have a DOS partition, the best idea would be to use DOSEMU emulator - DOSEMU can also access Linux partitions, where you may have your CD.ISO file waiting to be "grasped in your clever hands".

When you run MAKEBT.EXE at the DOS prompt, it will ask for the full path and filename of the ISO file to be modified: you will type the name of the ISO file with multiple boot diskette images in it, for example, CD.ISO, and you will see the following screen:


Make Multiple Boot CD-ISO Image Modifier ver 1.02

ISO File path and name: cd.iso

Bootable Disk Image Boot media type Default LBA

------------------- --------------- ------- --------


1 ) FBSD.IMG             1.44M Floppy             Y

2 ) LINUX.IMG          2.88M Floppy               -

3 ) PLAN9.IMG          1.44M Floppy               -

4 ) QNX.IMG              1.44M Floppy               -

5 ) OPENBSD.IMG     2.88M Floppy              -

6 )

7 )

8 )

9 )

10 )

<TAB> = move between fields, up/down arrows = move between rows, F1 = Confirm

Press 'y' key to make this image as default boot


BC stands for Boot Catalog. You just write boot.cat and don't worry about it anymore, as you already used this string in the above mkisofs command (it is, however, important that the ISO image file contains the string "boot.cat" in it). Now you carefully type the names of the images. You have to type the name of images in the DOS 8.3 format (this is a DOS restriction for file names - the file may have only 8 characters and suffix 3 characters maximum).

In the middle of the screen you will choose from 1.44MB floppy emulation, 2.88MB floppy emulation, hard disk emulation, or no emulation. We will only use 1.44MB and 2.88MB emulation (if you want to make a hard disk emulation, make a 650MB Linux partition and copy there the filesystem of your Linux system you booted your hard disk from - experiment...) Use the right keyboard arrow to select between the types of emulation. On the right of the screen you have to choose one bootable image as the default one by pressing "Y".

When you are finished, press F1 (you may try this several times, as the program may not  respond everytime). The program is intelligent - if you typed the image file name incorrectly, you will receive a warning message (after pressing F1). Do not include any descriptions for boot images in the menu that follows after pressing F1, as this feature is mostly exploitable in SCSI CD-ROMs and I haven't studied it very much.

That's it. Now you may burn your CD.

cdrecord -v speed=8 dev=0,0,0 /cd.iso

When you boot the CD, you will not see descriptions for operating systems, only numbers. The first and the second number will (0,1) usually stand for the same operating system. I had not much time to experiment with this issue, but a good idea would be to write down the number, so that you know which operating system you are going to boot from.

We deal here with diskette images and emulation, so if you boot your images with the multiple boot CD you just created, you may access your CD-ROM by typing "mount /dev/hdc /mnt", for example, and have also access to your /Soft directory, where you may have other utilities you plan to work with later. In case of a DOS system disk, you should include drivers to access the CD-ROM.

If you want to study or make a Linux program to patch the ISO file, you can compare an ordinary ISO image file with one boot possibility only with the ISO file patched by the makebt.exe utility. A good binary patcher is a diff utility by Giuliano Pochini. Bdiff is a simple and small program for making what the very common utilities "diff" and "patch" do with text files, but also works with binary files. It may be downloaded from: http://space.virgilio.it/g_pochini@virgilio.it/ - however, both ISO files must be identical. The diff utility (for comparing files) will show you the place (offsets) where the information with a multiboot flag was written. It is sector 17 (Boot Volume Descriptor) and the Boot Catalog Sector.

I created many multiboot CD's with the above information and I have never experienced a problem. But first, in order to avoid writing unusable CD-Rs - I had some problems making my own OS/2 images - burn the ISO image on rewritable CD-RW disks. Enjoy!

Copyright © 2002, Juraj Sipos. Copying license http://www.linuxgazette.net/copying.html
Published in Issue 85 of Linux Gazette, December 2002

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