> I want a telnet user to be restricted to his home directory and
> can't traverse backwards, how can I do that?
Disable their shell.
Think about it. How do they run sh? How do they run ls? How do they
run $FOO? What you want is futile.
You can restrict the shell itself (rbash, etc), but you can't be sure
every other single program the user can run from the won't do
<whatever it is you're trying to prevent> unless you audit a *lot* of
code.
Why do you want to do this anyway? Do you think your security is weak?
--
There is no TRUTH. There is no REALITY. There is no CONSISTENCY. There
are no ABSOLUTE STATEMENTS. I'm very probably wrong. -- BSD fortune(6)