temporary directories

[leichter_jerrold at emc.com (Leichter, Jerry)]

| Not on Unix, but I tend to use temporary names based on the Process ID
| that is executing.  And of course file protection prevents malevolent
| access.
| 
| But for a temporary file, I will specify a file that is not in any
| directory.  I presume there is such a capbility in Unix.
You presume incorrectly.  You're talking about VMS, where you can
open a file by file id.  The Unix analogue of a file id is an
inode number, but no user-land call exists to access a file that
way.  You can only get to a file by following a path through the
directory structure.

In fact, all kinds of Unix code would become insecure if such a
call were to be added:  It's a common - and reasonable - assumption
that accessing a file requires access to the (well, a) directory in
which that file appears (not that it isn't prudent to also control
access to the file itself).

One can argue this both ways, but on the specific matter of safe
access to temporary files, VMS code that uses FID access is much
easier to get right than Unix code that inherently has to walk
through directory trees.  On the other hand, access by file id
isn't - or wasn't; it's been years since I used VMS - supported
directly by higher-level languages (though I vaguely recall that
C had a mechanism for doing it).  A mechanism that requires
specialized, highly system-specific low-level code to do something so
straightforward is certainly much better than no mechanism at all,
but it's not something that will ever be used by more than a
small couterie of advanced programmers.
                                                        -- Jerry