Trouble making bootable USB from ISO image
Hello
I'm trying to use Stretch to write a .ISO image to a USB device. The
image is the Windows 10 installer (please don't flame me! It's part of
an education project for my son!) which I downloaded from Microsoft, and
which they claim should be able to be written to a USB device. Microsoft
would have me write the ISO using a tool of theirs, but since I don't
have another Windows device that isn't possible. They say that in that
case the ISO can be written to a pen drive using OS-specific tools.
I'm attempting to test the image before booting the installer on the
final computer earmarked for sacrifice to this project. The computer I
am testing on has successfully booted from a pen drive before and the
pen drive I am using has been used to boot this computer before, albeit
not this image.
After downloading the .iso file, I plugged in the USB stick. Because it
had something recognisable on it already, it auto-mounted. It was
assigned device /dev/sdf and mounted somewhere under /media, I don't
remember the exact path.
So as root I did:
cp <ISO file> /dev/sdf
and waited a while. Eventually the copy finished (the ISO is between 5
and 6 GB, the capacity of the drive is 16GB). Then I did
eject /dev/sdf
and after a long wait, that command came back with no errors. I then
removed the drive.
On plugging the drive back in, Stretch can recognise there is a
filesystem on it and mount it. I can see the usual efi structure for
booting etc.
BUT, the test computer refuses to recognise it as bootable. The BIOS can
evidently see the device is there and is an option to boot from, but
when I try it fails and falls back to the machine's internal hard disk.
If I disable booting from the hard disk in the BIOS, it fails to boot at
all with an error message essentially saying "give me something to boot
from".
There is some discussion on the internet suggesting that the pen drive
additionally needs to be marked as bootable. I thought that was an old
pre-GPT partitioning thing, and I also would have thought that if it
were relevant the .ISO image should contain the necessary settings, but
hey I'll try anything once... gparted was suggested as the tool to mark
the partition as bootable but when I fire up gparted it doesn't seem to
recognise the pen drive as it says the 16GB pen drive is "14.7GB
unnallocated" and says there is no partition table on it. This despite
the fact that it auto-mounts when I stick it in while Stretch is
running...
I'm confused whether the problem is in something I did or didn't do
while copying the ISO image, or if there is something I need to set in
the BIOS to get it to boot (I have a dim memory of fannying around with
various settings a very long time ago when I first got booting from USB
to work, and the CMOS battery on this motherboard has died at least once
since then). I'm extremely doubtful that the ISO image just doesn't
work, and I know for a fact that this computer can be persuaded to boot
from a pen drive and that this pen drive has been used successfully in
the past.
Any suggestions of what I could do to diagnose the problem?
Thanks in advance
Mark
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