loginid vs. uid.

[Christopher R Volpe]

What exactly does su have to do (when given the "-" option) to *completely*
change your identity so that applications like mail think you are the
person you su'd to rather than the person you su'd from? I once experimented 
with a program (setuid to root) that set real and effective group and
user ids to root, and then execed a c shell. "who" reported the name
I logged in under (which makes sense because of the utmp file), but
applications like mail still thought I was the person I logged in under.
Does mail use the utmp file as well? I tried changing enironment
variables such as HOME and LOGNAME, but they had no effect. 

Chris Volpe
GE Corporate R&D
volpecr at crd.ge.com