usb bootable stick

[Rick Stevens]

On 10/16/2015 02:14 PM, Tod Merley wrote:
> What of the device firmware, boot capability contained therein,
> performance optimization contained in the section between the front of
> the drive and the start of the provided partition, and and crazy often
> auto-mount firmware “CD-ROM” provided as a method of device software
> availability and possible auto-installation in Windows systems set up to
> do so?

If you are unlucky enough to get stuck with a USB thumb drive that has
U3 stuff on it, generally they've got it stuffed so that a normal write
to those blocks won't work unless you do some "magic" and delete the U3
stuff first. If you don't, writing your bootable ISO to it is useless
as you can't overwrite the boot loader on the thumb drive.

I refuse to buy thumb drives that have that crap on it. God knows what
evil software they've stuffed into it (remember the stupid KVM that
had code that would force your browser to go to a specific website?)

>
>
> On Fri, Oct 16, 2015 at 9:43 AM, Rick Stevens <ricks at alldigital.com
> <mailto:ricks at alldigital.com>> wrote:
>
>     On 10/16/2015 02:36 AM, Ranjan Maitra wrote:
>
>         On Thu, 15 Oct 2015 22:44:20 -0700 Joe Zeff <joe at zeff.us
>         <mailto:joe at zeff.us>> wrote:
>
>             On 10/15/2015 09:14 PM, Ranjan Maitra wrote:
>
>                 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).
>
>
>             If the device isn't mounted, there's no mount point for the
>             command to
>             write to.
>
>
>         Correct. Then where would it write to?
>
>
>     If you write to a /dev/sd* node, you write to the raw device whether
>     it's mounted or not. If that device happens to be mounted at the time,
>     then things are going to get very ugly with the mountpoint as the
>     filesystem associated with the mountpoint won't necessarily know about
>     what you've done to the underlying device--the filesystem's idea of
>     what's on the device will be different than what's actually on the
>     device. Some programs do take care to not permit you to write to a
>     raw device if it's mounted to keep this from happening.
>
>     Mountpoints are just directories. If you write to the mountpoint
>     _without_ any device being mounted there, then you write into the
>     mountpoint directory as you would any directory. If you then mount a
>     device at that spot, the contents of the device will hide the content
>     existing in that mountpoint directory until you unmount the device.
>     Then the content you wrote to that directory will reappear.
>
>     In general, if the target of some operation is a node in /dev then do
>     try to ensure it (or any part of it) is _not_ mounted. One of the
>     easiest ways is to use "mount | grep <device>", e.g.
>
>              mount | grep /dev/sdb
>
>     If you don't get any output, then you can be relatively sure that no
>     part of the physical device /dev/sdb is being used as a filesystem.
>     ----------------------------------------------------------------------
>     - Rick Stevens, Systems Engineer, AllDigital ricks at alldigital.com
>     <mailto:ricks at alldigital.com> -
>     - AIM/Skype: therps2        ICQ: 226437340           Yahoo: origrps2 -
>     -                                                                    -
>     -         "OK, so you're a Ph.D. Just don't TOUCH anything!"         -
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>


-- 
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- Rick Stevens, Systems Engineer, AllDigital    ricks at alldigital.com -
- AIM/Skype: therps2        ICQ: 226437340           Yahoo: origrps2 -
-                                                                    -
-                       When in doubt, mumble.                       -
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