process group question

[Gerry Baumgartner]

In article <1990Feb9.111849.22479 at axion.bt.co.uk> nwinton at iona.axion.bt.co.uk (Neil Winton) writes:
>POSIX has basically similar functionality to BSD but implemented via
>`session ids'.  I can try and give details if you want ...

Job control provided by POSIX is not really implemented via session id's.
Actual controlling of jobs within a session is still done via process groups
similar to the way BSD systems do it.

However, BSD systems allowed process to join process group 0.  This allowed
a process to aquire any terminal it opened as it's controlling terminal, and
subsequently join the process group of the current foreground process group.
This can be view as somewhat of a security breach.

POSIX disallows this by allowing a process to change to a process group that is
equal to it's own pid (make it now a process group leader) or to a process
group that must already exist and be in the session of the calling process.
So, session id's are used keep process within their "login session".  
-------------------------------------------------------------------------------
Gerry Baumgartner                |    gerry at ssd.csd.harris.com 
System Software Development      | or gerry%ssd.csd.harris.com at eddie.mit.edu
Harris Computer Systems Division | or ...!{mit-eddie,uunet,novavax}!hcx1!gerry
Fort Lauderdale FL 33309         |
-------------------------------------------------------------------------------