[K12OSN] Dropbox question

Petre Scheie petre at maltzen.net
Thu Dec 21 17:23:48 UTC 2006

Les Mikesell wrote:
> On Thu, 2006-12-21 at 09:30 -0600, Petre Scheie wrote:
>>> One mandatory suggestion if you want to do it this way, set the sitcky 
>>> bit, making the permissions 3777. This will prevent students from 
>>> deleting one another's files.
>> Users can't delete each other's files even without setting permissions to
>> 3777 because the default permissions, as dictated by the umask, set Other
>> to r-x.  Even if the folder the files are being put into is set 777, the
>> files themselves will still be owned by the student who put them there,
>> and the Other perms will be rx, meaning no other student can delete those
>> files.
> That's not true.  On unix-like systems, the ability to delete files is
> determined by the containing directory permissions, not the file itself.
> The sticky bit on the directory changes this so that you must also have
> write permission on the file to delete it.

Ah, yes, you are correct.  I was deceived by the lack of a write permission for Other on 
the file, and by Nautilus's indication that the file was read-only for everyone but the 
creator.  Serves me right for not actually testing it.

Further, Burke was correct in stating that setting the sticky bit for Other (3777) will 
prevent anyone but its owner from deleting it, save for the teacher who is a member of 
the group which has write permissions on all files.


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