There is a vital thing to remember about computer security: securityis not math, security is people . Thinking that security is math getsyou mathematical perfection and white hot disasters.

(These disasters happen for much the same reason that firewalls aredangerous: people think that they are completely protected once theyhave math on their side and thus don't take any further precautions.)

You can create the most mathematically perfect computer security systemknown to humanity and people will misuse it, or bypass it. If you makeit

Lots of Unixes have some form of 'loopback' mounts, where you can mounta bit of an existing filesystem somewhere else; they're called loopbackmounts by analogy with the loopback interface. The general idea behindthem is that they are a more efficient (and easier to use) version ofdoing an NFS mount from localhost .

(I suspect that Sun originated the idea, but I'm not sure.)

Linux's bind mounts (so called because they are done with mount--bind ,