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Re: Trouble making bootable USB from ISO image




On Sat, May 04, 2019 at 09:54:52AM -0000, Curt wrote:
> I'm intervening here merely to point out that just because the user's
> external usb device is auto-mounted does not mean that said device
> cannot be unmounted by the usual methods (at least I have yet to
> encounter Greg Wooledge's auto-mounter from Hell that will not permit
> it). 

I never said anything about not being able to unmount.

If a partition from a medium (USB or whatever) is mounted read-write,
during the time that you execute a "cp foo.iso /dev/sdx" command
to write a disk image to said medium, you are going to have problems
of the corruption kind, not of the "cannot unmount it" kind.

Unmounting the file system is going to write some information to the
medium in the place where the operating system thinks the file system
is.  But that file system isn't there any more, because your cp (or dd
or whatever) command overwrote it.  But the file system driver, upon
unmounting the file system, is supposed to write stuff -- flushing
the cache, setting the "this has been cleanly unmounted" flags, etc.
All of that stuff that it writes will corrupt whatever part of the ISO
image it happens to land on.