Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!novavax!hcx1!gerry
From: gerry@SSD.CSD.HARRIS.COM (Gerry Baumgartner)
Newsgroups: comp.unix.questions
Subject: Re: process group question
Message-ID: <2963@hcx1.SSD.CSD.HARRIS.COM>
Date: 13 Feb 90 19:59:40 GMT
References: <1281@sun2.summer.bt.co.uk> <1990Feb9.111849.22479@axion.bt.co.uk>
Sender: news@hcx1.SSD.CSD.HARRIS.COM
Organization: Harris Computer Systems, Fort Lauderdale, FL
Lines: 23

In article <1990Feb9.111849.22479@axion.bt.co.uk> nwinton@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@ssd.csd.harris.com 
System Software Development      | or gerry%ssd.csd.harris.com@eddie.mit.edu
Harris Computer Systems Division | or ...!{mit-eddie,uunet,novavax}!hcx1!gerry
Fort Lauderdale FL 33309         |
-------------------------------------------------------------------------------