Booting from a USB stick

Mikkel L. Ellertson mikkel at infinity-ltd.com
Tue Oct 23 03:43:44 UTC 2007


Timothy Murphy wrote:
> Mikkel L. Ellertson wrote:
>> Are you sure the USB stick was mounted read-only, or was it just the
>> compressed file system that was mounted read-only? The reason I ask,
>> is because what this install does is copy the compressed file
>> system, and the files needed to load/boot it over to the USB stick.
>> The main advantages of using the USB stick are access speed, and
>> physical size.
> 
> I'm sure you are right, though I don't completely understand
> what you are saying.
> "Mount" showed /dev/sdb1 (the memory stick) as ro.
> I then ran "mount -o remount,rw /dev/sdb1"
> and it became rw.
> However none of the changes I made when sdb1 was rw seemed to "stick";
> all disappeared when I re-booted.
> 
One of the problems is that the / file system is not /dev/sdb1, even
though that is the USB drive. The root file system is really a file
on the USB drive. This is a compressed file system designed to be
used on read-only devices, and is not designed to be modified once
created. Because of the way the live CD does things, you can make
changes, but as you noticed, they do not survive a reboot.

If you are interested in the details of how it works, you can read
up on cramfs. I believe it is also covered on most of the sites that
have live CD's, as this is a common way to pack more file then would
normally file on a CD into the live CD.

If you want a fully functional Linux system that remember changes,
and lets you update packages, you have to use a more "conventional"
install that creates "standard" file systems on the drive. I know an
expert install from the install DVD or boot CD will let you do this,
but I don't remember if the live CD's will. You will have to fix the
Grub configuration after install, but that is not a big deal.

Mikkel
-- 

  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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