newbie's question on file permission

[Aart Koelewijn]

On Fri, 01 Aug 2008 20:37:41 +0200, Zhengguo Xu wrote:

> Greeting all!
> 
> Recently I encounted a strange problem (or it maybe very obvious for you
> guys) while copying files and I'd like to ask a question on file
> permission in linux.
> 
> I have a file, lets say 'biology.ppt' and it has permission as follows
> and i am the owner and it belongs to group 'root'
> 
> -rwx------
> 
> i want to change it to group, say, 'test', and give permissions to
> everyone to read and write and execute, what's wrong when I run the
> following command?
> 
> sudo chgrp test biology.ppt
> sudo chmod 777 biology.ppt
> 
> nothing happened when i run these commands and i tried them with and
> without sudo. the file still has the permission -rwx------ and root is
> still the group.
> 
> if it matters, the file is on a usb disk mounted in /media
> 
> i also tried to create some file in my home directory and i can change
> it as i want with the same command.
> 

I have no experiences with usb disks, but in this case I suppose the usb 
disk will have I filesystem that does not support owner.group settings of 
files. I suppose the ownership and permissions of biology.ppt will be 
those of the whole disk and can only be changed for the whole disk, not 
for separate files on it.

Aart