usb bootable stick

[Fred Smith]

On Thu, Oct 15, 2015 at 11:14:53PM -0500, Ranjan Maitra wrote:
> > Ranjan Maitra:
> > > In my experience with Fedora (only), I have found that mounting is
> > > essential. Otherwise it writes to the mount point, but not the device.
> > 
> > Why would anyone think that a command like:
> > 
> >   dd  if=boot.iso  of=/dev/sdb  bs=8M
> > 
> > Is going to write to anywhere else than /dev/sdb?
> 
> No, I would not think so. But if the device is not mounted, would it not write to the mount point, especially because you are doing so as root (so nothing to stop you). This logic seems to make sense to me, and indeed is what happens when I have done it accidentally (without mounting the USB drive).
>  
> > In general, trying to do a direct write to a device, while it's mounted
> > on the filesystem, is inherently risky.  You stand a very good chance
> > that the mounted filesystem is going to stomp over the top of your raw
> > write.  The only way I could see it *not* stomping over it, is if you
> > yanked the USB drive out without dismounting it (another stupid thing to
> > do).
> 
> Agreed to this last point, but not what happened.
> 
> I don't know and I am not an expert. However, from experiment, observation and inference, I have noticed that unless the usb is mounted, dd does not copy to the device. (This happened as recently as last week).
> 
> Many thanks and best wishes,
> Ranjan
> 

One thing I've noticed in the past is: if the USB device is auto-mounted when you
insert it, and if you then right-click/unmount, that the device node (in /dev)
is also removed. So, if that's what is happening, instead of using the right-click
menu to unmount it, go to a terminal and (as root) type "umount /dev/sdxx",
which unmounts the drive but leaves the node there, so that you can then write
to the drive as a raw device.

Make sure you use the right value for /dev/sdxx, otherwise you'll write all over
some other drive. (The voice of experiencek, here... believe me, it ain't pretty!)

-- 
---- Fred Smith -- fredex at fcshome.stoneham.ma.us -----------------------------
   "For the word of God is living and active. Sharper than any double-edged 
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---------------------------- Hebrews 4:12 (niv) ------------------------------