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From: mike@x.co.uk (Mike Moore)
Newsgroups: comp.unix.misc
Subject: Brain Teaser
Summary: script /bin/sh
Message-ID: <Oct90.150551.3649@x.co.uk>
Date: 4 Oct 90 15:05:51 GMT
Reply-To: mike@x.co.uk (Mike Moore)
Organization: IXI Limited, Cambridge, UK
Lines: 27

Here's one (do NOT actually do this, it appears to be lethal):

  mv /bin/sh /bin/sh.bin

create a shell script called /bin/sh with the following

if [ $USER = "root" ]
  then
    /bin/sh.bin
  else
    /bin/rsh
fi

log out and log back in (assuming that your passwd file has you set to
use /bin/sh

you can't (can't exec a shell of course).

now assume that *everyone* is set to use /bin/sh (including root), how
do you get out of this without rebuilding the operating system?  I don't
think there actually is one..... but....

-- 
---
Mike Moore
mike@x.co.uk or mike@ixi-limited.co.uk
Usual and obvious disclaimers... etc