Re: [gentoo-user] Re: [OT] Making a bootable USB flash drive from ISO image

[Neil Bothwick <neil@digimed.co.uk>]

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On Thu, 2 Oct 2014 21:38:36 +0000 (UTC), Grant Edwards wrote:

> > They did something, but it's not particularly special. All they did
> > was run isohybrid (from syslinux) on the ISO image. It uses unused
> > space at the start of the DVD ISO specification that is normally left
> > blank to hold a partition table so the image can be copied to a USB
> > drive and appear as a partitioned disk.
> 
> There must be a little more to it than that.  Does it also install
> along with a parition table some bootloader code that knows where/how
> to boot the ISO boot image?  [After a little googling] It also
> installs MBR bootloader code that knows how to find/load isolinux.bin:
> 
> http://www.syslinux.org/wiki/index.php/Isohybrid

Yes, the unused space contains the MBR; partition table and bootloader.
Plus it adds some more code at the end of the image.

I was also wrong in stating I use isohybrid for the LXFDVDs. I used to
but since switching to using GRUB to boot the DVDs, there is no need for
it. GRUB bootable DVD ISOs can boot from USB sticks by default.

That's the trouble with writing scripts to take care of routine tasks,
you forget when you are actually doing beyond running the script.

> Interestingly, it also created a second EFI boot partition which
> exists inside the main parition.

That must be a UEFI bootable disc. ISOs can have all sorts of strange
setups, I have to make the LXFDVDs readable on a Mac, which results in
an HFS+ filesystem being nested inside the ISO one.


-- 
Neil Bothwick

Become a gynaecologist, look up a friend today.

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