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I used instructions from PenDriveLinux.com to create a multiple-boot USB drive with some ISO images on it. I used Xubuntu 10.10 Desktop image and a Linux Mint 9 XFCE image. I was able to boot either of the two operating systems. Each one booted directly to the desktop however.

If I boot *Ubuntu from an ISO image which has been "burned" to a CD or a USB, I am presented with a menu prompting me to install or try the OS, test memory, etc.

Why does booting from the ISO go directly to the desktop, whereas the other method presents the OS menu first?

Update

menuentry "Ubuntu 10.10 Desktop ISO" {
 loopback loop /ubuntu.iso
 linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/ubuntu.iso noeject noprompt splash --
 initrd (loop)/casper/initrd.lz
}
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1  
Related: unix.stackexchange.com/q/665/250 –  phunehehe Jan 22 '11 at 2:10
    
Can you post the entry in grub.cfg? –  phunehehe Jan 22 '11 at 2:10
    
Thanks for the link. I've updated my question with the grub entry. –  SabreWolfy Jan 22 '11 at 8:10
    
Just noticed that my example above exactly matches the one Gilles' used below. –  SabreWolfy Jan 22 '11 at 8:37

2 Answers 2

up vote 3 down vote accepted

It's due to the bootloader setup on the potentially-multi-boot USB drive. The Grub configuration for the drive is set up to boot the various OSes directly: it contains entries like

menuentry "Ubuntu 10.10 Desktop ISO" {
 loopback loop /ubuntu.iso
 linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/ubuntu.iso noeject noprompt splash --
 initrd (loop)/casper/initrd.lz
}

Such an entry boots directly into the indicated operating system, bypassing the bootloader inside the ISO.

I think it would be possible to switch to a different configuration file with configfile (loop)/path/to/grub.cfg, if the bootloader inside the ISO is also Grub2 (which is not so common on CDs). Loading the bootloader inside the ISO would be difficult, as the bootloader would have to understand where to find its components.

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So the custom *Ubuntu menu presented when booting from a single-boot "burnt" CD/USB image is created by the bootloader in the image? This would then launch the ISO image itself with options depending on whether you wanted to install or just run the OS live? –  SabreWolfy Jan 22 '11 at 8:14
    
There is a loopback.cfg in the /boot folder in the ISO itself, which contains the various entries (try, install, test memory, etc.) which are presented when single-booting. I see that different options are passed in. I didn't realize that this menu was actually a modified bootloader/grub menu. –  SabreWolfy Jan 22 '11 at 8:40

You are using an old version of grub. sudo apt-get install grub2 and then try again

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1  
From syntax I can see (s)he's using the grub2. If you are referring to any bug which have been fixed (IMHO unlikely) please include it for reference. –  Maciej Piechotka Feb 12 '11 at 12:40

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