Extracting floppy boot image from ISO with dd?

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ol5

Member
Sep 17, 2020
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I know there are utilities that can extract the boot image from a CD ISO which can then be used to create a boot floppy or another bootable CD ISO. Anyone know if the differences in the boot header for a bootable FreeDOS floppy image, CD ISO or USB ISO is the sector number where the boot code is located? I think for floppies it is located at the first sector on the disk, but I don't know about CD or USB bootable ISOs. If it is just a difference in the sector number, I would think we should be able to use the dd command to extract a floppy image by starting at the correct sector of the CD or USB boot ISO and specify the number of sectors to extract.
 
I am not sure if you can use dd. The boot "file" may be of varying sizes depending on what type of boot ISO it is.

That being said, on Windows I have used 7-zip to extract the boot file. 7-zip shows it in a special folder called "[BOOT]".
If you install 7-zip on Linux (p7zip-full) you can use the 7z command to extract the file:

Code:
7z e isofile.iso '[BOOT]'

Here I'm extracting it from the ultimate boot CD iso. Note the 2KiB "Boot-NoEmul.img" file.
Capture.PNG
 
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It is good to know that option is available in the Linux version. That must be a Linux only option because it was not an option on the Mac and Window versions I have installed. I wonder if it is limited to ony ISOs with Linux boot code.
 
It is good to know that option is available in the Linux version. That must be a Linux only option because it was not an option on the Mac and Window versions I have installed. I wonder if it is limited to ony ISOs with Linux boot code.
No, this works on 7zip on Windows too. You can extract the boot image with either the 7zip GUI (File Manager) or the command line. Not sure about the Mac though.
 
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And sorry, I assumed you meant Linux when you were asking about dd. I forget that Mac OS X has most UNIXy commands too!
 
Mac has unzip in the Finder app, just dbl click the file. After you have the .img file you can use balena etcher to write it to any usb stick. Works perfectly on Linux and Mac.
 
Mac has unzip in the Finder app, just dbl click the file. After you have the .img file you can use balena etcher to write it to any usb stick. Works perfectly on Linux and Mac.
Not being a Mac user, I've been looking for some clear instructions for using the SR61.ZIP and the SR61.IMG file it contains for Mac users. I see from your posting that, as we would expect, opening the ZIP is built-in. So the challenge was how a Mac user might easily write the enclosed .IMG file to a USB thumb drive. And to that end, the balenaEtcher utility you referred to looks PERFECT for this. I love the fact that they highlight these features:
  • Validated Flashing: Etcher confirms that your flash has completed, enjoy peace of mind that your card will boot and isn’t corrupted.
  • Hard Drive Friendly: Etcher gives you warnings and hides your system drives by default to avoid accidentally wiping your entire hard-drive.
  • Beautiful Interface: Who said flashing SD cards has to be an eyesore. Etcher has an intuitive 3-step process with no command lines!
  • Cross Platform: Works for everyone whether you are on Windows, Linux or Mac with no complicated install instructions.
https://etcher.balena.io/#download-etcher

Nice find! Thanks!!!
 
I've run across Balena Etcher from installing Tails onto flash drives.

I haven't used it for a while, but a program called YUMI ( https://pendrivelinux.com/ ) might be worth checking out. Some time back I had a Windows version running on a flash drive with SR6.0 and a number of other ISO bootable images. It worked well.
 
I haven't used it for a while, but a program called YUMI ( https://pendrivelinux.com/ ) might be worth checking out. Some time back I had a Windows version running on a flash drive with SR6.0 and a number of other ISO bootable images. It worked well.
Thanks for the pointer, @Ralph. For the record, our biggest need is for Mac users, and it doesn't appear as though YUMI has a solution for them. SpinRite (and BootAble) will both create bootable USB thumb drives for Windows users. Ubuntu includes a nice "Disk Image Writer" utility and most Linux power users can simply use 'dd'. So it's the Mac folks for whom we want to find a good solution. :)
 
Thanks for the pointer, @Ralph. For the record, our biggest need is for Mac users, and it doesn't appear as though YUMI has a solution for them.
Hopefully the button to create an ISO doesn't vanish from the 4th release of SpinRite 6.1 given how many people with older non-USB bootable systems have yet to receive an email of the updated SpinRite version that they'll expect to be able to burn to a CD. For that feature to vanish would I think require a version number bump. I do see that it has to go away but I'd wait till 7.x to do that IMO.

As far as YUMI goes, I still use it to create multi-boot USBs with SpinRite on them for old industrial rack servers which for some reason only seem to accept ISOs, but that's a niche usage.