Changing permissions

D. Michael McIntyre michael.mcintyre at rosegardenmusic.com
Sat Jul 21 16:57:27 BST 2007


On Saturday 21 July 2007, Dotan Cohen wrote:
> You don't want to format that thing ext2/3. It won't be useable in
> WindBlows anymore, and thus the portability of the device is rather
> compromised. I suppose that you could tar files that you must keep
> permissions for.

You can do it if you never intend to use the stick with anything that isn't 
Linux though.  I expect.  I haven't actually done it, but I used to format 
floppies for Linux.  It should work.

> Note that I think that it is unusual that the execute bit would be set
> on files from an insecure device such as a USB stick. I haven't
> checked what this machine, does, though. Can someone verify their
> machine's behaviour?

The execute bit is set on *everything* by default, because there are no 
permissions in VFAT, and in order for the directories to be readable, they 
have to be executable.  Since there isn't any way to have fine-grained 
control without per-file permissions (you have to set up *one* set of fake 
permissions that are used for everything on the mounted VFAT filesystem) 
there isn't really a good way around this problem.  That's why the default is 
usually to use 777 on everything.

If you've copied something from a VFAT source that's a 777 (rwxrwxrwx) mess, 
you can probably fix it with something like this ($directory is the path to 
whatever directory in question, like /home/foo/junk_I_copied_from_Winderz or 
whatever):

    find $directory -type f|xargs chmod 640
    find $directory -type d|xargs chmod 750

(Or use 644 and 755.  I keep more restrictive permissions than are the default 
on most Linux systems.)

That will find all the files, then all the directories, respectively, and 
reassign more appropriate permissions to them.  That's probably sufficient 
for most situations, I think, though I didn't actually set up a test scenario 
and play with any of this for real.  I could be spouting nonsense about this 
777 thing, since it looks like none of the pictures I've copied off of my 
memory cards have weird permissions.  Oh well, if I go on record babbling a 
torrent of bullshit because I think I'm such an all-knowing genius that I 
don't have to bother fact checking before writing a treatise on a particular 
subject, then it won't be the first time.  At least I'm honest with myself, 
eh?  :D
-- 
D. Michael McIntyre 



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