hiding files under a mount point.

[Jeff Leyser]

In post <1991Mar18.045734.5114 at brolga.cc.uq.oz.au>, ggm at brolga.cc.uq.oz.au (George Michaelson) says:
!
!If you have some files in a directory eg /usr (on the root partition)
!and you mount the filesystem /usr over them, they become "invisible".
!
!How "invisible" are they? Can this be exploited meaningfully by sysops
!or others to provide secure online storage of files you don't want
!mortals to know about? (/usr is a bad example. unmounting makes the
!system pretty useless. some other places might be more bearable.)

They're completely invisible, at lease to all "useful" utilities.  The
only way to manipulate the "hidden" would be by i-node numbers, and I
don't think anything other than fsdb will be able to do that for you.
Of course, unmounting the "overlay" will allow you to manipulate the (no
longer) hidden files in the usual manner.

But there several better ways to do what (I think) you want.  Place the
files in a directory owned by root, with permission of 700.  Users will
see the existence of the directory, but won't be able to tell what is
inside.  If you want to go one step further, and hide the directory name,
place the "good" directory inside a dummy directory, and set the dummy
to 700, too.

This isn't very internal-ish.  Followup to comp.unix.questions, please.
-- 
Jeff Leyser                                     jeffl at NCoast.ORG