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Re: [K12OSN] Dropbox question



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.

Petre


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