Chainload El-Torito ISO - ArchWiki

# Chainload El-Torito ISO

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Reason: please use the first argument of the template to provide a brief explanation. (Discuss)

Work in progress. This is what I've researched so far, I'll add more when I find more.

Aims:

- To boot multiple ISOs from a single USB flash drive.
- Drive should be multi-purpose. Space for other files such as documents.
- Quick easy setup; deal more with files and less with partitions. This makes the drive more portable and flexible on legacy OSs. Drive should have .iso files rather than iso9660 partitions.
- Setup should be reliable on various BIOSs for more portability.
- The ability to remove the drive after boot would be very useful.

## Gujin MBR & ISO9660 Partitions

This solution inspired me but has it's problems: Install_from_USB_stick#Gujin

### Problems

- When Gujin is installed as the MBR it requires it's own partition. This can be a nuisance to set up properly. If this partition is mounted and written to, it becomes corrupt.
- Most GNOME installations automount all the many iso9660 partitions I have.
- I usually duplicate the ISOs as files and partitions.
- Gujin isn't able to boot ISOs on some BIOSs even though CDs can boot.

After much research I came up with some improvements and information. I'm trying to present these improvements in a modular fashion, rather than giving possible complete solutions.

## Grub4Dos

Grub4Dos is a fork of Grub Legacy which is actively maintained and has some useful ideas. It is familiar to Grub users, easier to manage and opens up some new features.

- Make fat32 filesystem on partition 1.
- Install Grub4Dos to MBR.
- Copy Grub4Dos files to partition 1's / or /boot.

### Gujin Floppy

The need for a Gujin partition is removed by the use of a Gujin boot floppy image which is booted from Grub4Dos.

- Get Gujin standard tarball.
- Extract floppy image

    tar -xzf standard-2.8.1.tar.gz full.img.gz -O | gzip -d > gujin-2.8.1.fdi

- Edit menu.lst, add:

    title Gujin Boot Loader 2.8.1
    map --mem /boot/gujin-2.8.1.fdi (fd0)
    map --hook
    rootnoverify (fd0)
    chainloader (fd0)+1

Grub4Dos can boot the Gujin floppy image which then generates the menu of available ISOs.

### Memory Mapping

Files can be loaded into memory first, allowing for flash drive removal.

    map --mem From... To...
    map --hook

### Workaround For Crap BIOSs

Some BIOSs cannot boot from CD or USB drives, or fail to enter setup or boot menu.

- Install a Grub clone on the HDD if none already.
- Chainload flash drive. From Grub commandline:

    chainloader (hd1)+1
    boot

## CD Emulation

Many ISOs including Arch's require emulation.

- Gujin - I'm not sure if Gujin is an emulator or uses some other trick.
- isoemu - Sounds right but actually just uses INT13h. http://www.911cd.net/forums//index.php?showtopic=8955
- Grub 2 - Apparently Grub 2 plan to support el-torito chainload to ISOs but they do not seem to regard it as a priority or always realise what the actual goal is.

http://grub.enbug.org/FeatureRequests http://savannah.gnu.org/bugs/?10780

### Self-contained ISOs

Some ISOs have all data needed for boot in the kernel and ramdisk files. They can be booted directly from Grub4Dos without emulation.

### ?INT13h & Real Mode?

When an OS is in 'real mode', it hooks INT13h BIOS interrupt call and doesn't require emulation. Old or very minimal OSs stay in real mode but new and advanced OSs such as Linux leave real mode. At this point they crash unless properly emulated.

Not sure how accurate I am; I do not fully understand this.

### Gujin ISO Modification

According to the website, Gujin can modify .iso files, presumably so that they can be booted directly without emulation. I haven't tried this yet and can't find much info on it.

## Physical Workaround

Maybe, instead of a flash drive, a USB SD card reader and some SD cards could be used instead. Still a hassle though.

## Red Herrings

When searching, I found quite a lot of information on how to chainload a *REAL* CD rather than a .iso file or iso9660 partition. For example: http://www.lrz-muenchen.de/~bernhard/grub-chain-cd.html http://cutecomputer.wordpress.com/2006/10/10/boot-cdrom-through-grub/

I also came across alot of info on how to boot self-contained or INT13h ISOs.

Category:

- Boot process