setpgrp question

[Conor P. Cahill]

In article <6863 at cbnewsh.ATT.COM>, skumar at 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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