Non-booting machine and missing user rights on USB drives

[Ari Torhamo]

ma, 2010-01-11 kello 17:35 +0100, Markus Schönhaber kirjoitti:

> The users are given the right to do what they want with their own files
> on their own devices they plug into their own computers.

The user in question is the owner of the files, the USB drive and the
computer.

> The important question is: which *are* the user's own files?

The files on the USB drive and the computer.

> Who owns a file or directory is determined by the *user ID* stored in
> the file's inode. This means, for example, if you create a directory as
> the user with ID 1000 and don't grant permissions to anyone else, a user
> with an ID other than 1000 (or 0) will not be able to access this directory.
> WRT the problem you're facing: the UID of the live CD user is almost
> certainly different from the UID the user of the installed system had.
> Which means, from the system's perspective, the files on the USB drive
> (or internal drive, for that matter) are *not* the (live CD) user's own
> files.

When it's possible to override the permissions with one command from the
command line of the live CD (start Nautilus with gksudo, for example),
why not totally bypass this step, or perhaps just ask the user if he
*really* want's to work with the files and then let him do that? The
protection the current arrangement gives is worth nothing, but brings a
lot of trouble for less knowledgeable users.

> You'll see this on any file-system that supports ownership and access
> control, since it's exactly the system's job to ensure that the given
> rights are respected and enforced.

And good usability means that these policies don't cause unnecessary
trouble to users.

> If you want to allow users to write to a device regardless of their UID,
> either adjust the permissions of the device/file/directory 

Ask a few non-technical Ubuntu users to change the permissions for a
file that belongs to root without helping them with a word, and come
back to tell me your success rate...

> accordingly
> or use a file-system like FAT/FAT32 that has no idea of ownership or
> permissions and therefore won't offer any protection at all.

Wouldn't it make more sense to improve usability, than ask people to
move to unsafe file systems? The most accute problem is that you can't
change user permissions from root to user from the graphical user
interface. This is something that even many non-technical people
sometimes need to do. When their system doesn't boot, but they are able
to use the live CD, they may want to rescue their files from the hard
disk, or perhaps they work from the live CD and save files into a USB
drive until someone comes and fixes their system.

-Ari-