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Old 05-25-2008, 10:47 AM   #1
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BootLoader cd to usb drives

ok so heres the problem, i have 2 usb drives with seperate distrubutions of linux (fedora, and slax) and im trying to make a cd that will allow me to simply plug in a usb drive and boot off of it on machines that dont support usb booting, iv searched a few places but havent found a way to do this with multible usb drives running different distros.

any help would be appreciated
Old 05-26-2008, 04:07 AM   #2
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Your CD will need:
1. the initrd and kernel images of every distro you want to boot from HD
2. a startup script (in every initrd) which mounts the usb storage drivers, enumerates the HDs, and checks each HD to see if that is the one with the appropriate 'root' filesystem

Now if the script in [2] finds the right HD, then it can mount the HD partition as 'root'. If it doesn't find the HD, it needs to leave 'initrd' as root and at least drop you into a system that has enough functionality available for you to poke around and find out what's going on.

As you can probably imagine, this can be a nuisance at times because changing the kernel on each HD means you need to rebuild the initrd and CD.

The CD can never boot directly to a USB HD if the BIOS does not support USB booting. The reason is that the BIOS needs to provide the initial access to load the kernel and initrd (if you use initrd). So no BIOS support = effectively no HD to boot from. To be able to access the USB HD, you need an initialized kernel with the proper drivers booted - that is why your CD needs those initrd images - from there you mount the USB HD and finally 'chroot' to the final (r/w) root system. There are many good things about this approach anyway - for example, the system running under initrd can run fsck on the final root partition before mounting it.

By the way, there is no need for multiple USB HDs - you can have as many distros as you want on the one HD (even share directories such as 'home' if you want) - this really has insignificant effect on how you prepare your boot CD.

If that all sounds like ancient Arameic (or Sanskrit, Minoan, etc) then the answer is:
Unfortunately, the best preparation for what you want to do is to go build your own system from scratch (see Then take apart the *.iso image from a suitable distribution (Debian is OK for this) and study the entire bootup process from the "init" program on to the mounting of the final filesystem. When you've done all that, then it's pretty easy to see how to do what you want. Unless you have a lot of free time and really love doing this stuff, give yourself about 3 months to get up to the level of expertise needed to do what you want.

No 'quick' answers for this one; this is kind of like asking 'how do we put someone on the moon and get them back alive?'
Old 05-26-2008, 10:23 AM   #3
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well the only reason im using (now 3) multible drives, is because each one is taking most of my 1 gig of space, so i cant fit them all on to one drive, ill probably get a bigger drive that i can partition out to my current setup on the 3 drives, however right now this method seems to work just fine.... well if the computer can usb boot that is....

thanks for the help, i guess i was kinda hoping that i could get a boot loader to load a boot loader to boot the drive *shrugs* but that was kind of a long shot to begin with, ill go with what you have and start compiling that disk

Edit: probably should have mentioned that these are thumb drives, not full blown hard drives, thus the 1 gig of space max

Last edited by NIN-Master; 05-26-2008 at 10:38 AM.
Old 05-27-2008, 07:56 PM   #4
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Here is the ticket.

A full installation from a USB drive would not work because you can have only one Linux root directory system inside a CD. In other word there is no separate partition in a CD or DVD. Therefore the best way is to get the different iso files onto the same DVD disc.
Old 05-27-2008, 08:18 PM   #5
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one word.... persistence.... some distros allow you to save your state to a usb thumb/pen drive however not all

although I'm working on getting the usb drivers loaded ... for some reason it isn't working right in my virtual box machine...

though it could be because I'm doing something wrong, which wouldn't be much of a surprise...

Last edited by NIN-Master; 05-27-2008 at 08:22 PM.


boot loader, cd, usb

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