Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!virtech!cpcahil
From: cpcahil@virtech.uucp (Conor P. Cahill)
Newsgroups: comp.unix.questions
Subject: Re: setpgrp question
Keywords: setpgrp, unix system call
Message-ID: <1989Dec24.222740.8645@virtech.uucp>
Date: 24 Dec 89 22:27:40 GMT
References: <6863@cbnewsh.ATT.COM>
Organization: Virtual Technologies Inc.
Lines: 33

In article <6863@cbnewsh.ATT.COM>, skumar@cbnewsh.ATT.COM (swaminathan.ravikumar) writes:

> By reading different sources I found out that a process can
> break its control terminal by calling "setpgrp". I don't
> understand this 100%. Why should the process lose the control
> terminal? why do you need "setpgrp"?

setpgrp() is one of the steps that should be executed by a daemon
process at initialization time.  It does disconnect the terminal from 
the controll tty and therefore should only be used by programs that
no longer wish to be associated with a terminal.

Note that it does not disallow the use of stdin/stdout/stderr.  These
are file pointers that are already connected to file descriptors that
read/write to a terminal.  However, it does effect the ability of the
program to re-connect with the terminal by opening "/dev/tty" (which
is exactly what pg tries to do).

> I know that it is used to group processes to receive
> signals. Does this mean that the processes in the group cannot
> use stdin/stdout. I would like to hear from anybody who has used
> this call in a real application to understand this better.

In reality you shouldn't use setpgrp() unless you want to run without
any user interaction on the terminal (i.e. a background process or 
a daemon process that is supposed to be run in the background).


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