RE: Switching between foreground and background

["Mariano Moreyra" <moremari@aca.org.ar>]

I don't know if that's the way to gain daemon behavior. If you fork twice,
your process stills attached to the controlling terminal.
I guess you could finish that terminal session without problem. But I think
that a real daemon has to detach him self from the controlling tty.
You can do that, like Raghu said, calling setpgrp and setsid and closing
stdout an err.
There is also a function in unistd that does all of this for you.

int daemon(int nochdir,int noclose); (see "man daemon")

Don't know if exists in all unix or linux distros. But it seems to work.
Saludos.

Manuk


-----Mensaje original-----
De: linux-c-programming-owner@vger.kernel.org
[mailto:linux-c-programming-owner@vger.kernel.org]En nombre de John T.
Williams
Enviado el: Martes, 23 de Septiembre de 2003 13:07
Para: rvk@gsecone.com; John T. Williams
CC: Silambu Chelvan; linux-newbie@vger.kernel.org;
linux-c-programming@vger.kernel.org
Asunto: Re: Switching between foreground and background


I have to admit that I don't know why, but every resource I've ever read
about causing programs to gain daemon behavior has involved forking 2 times
and then starting the program code.  If anyone here does know why, I'd would
be happy to hear it.



----- Original Message -----
From: "Raghuveer" <rvk@gsecone.com>
To: "John T. Williams" <jtwilliams@vt.edu>
Cc: "Silambu Chelvan" <silambu_mdu@yahoo.com>;
<linux-newbie@vger.kernel.org>
Sent: Tuesday, September 23, 2003 7:01 AM
Subject: Re: Switching between foreground and background


> John T. Williams wrote:
>
> >I think part of the problem here might be conceptual.
> >
> >If I understand what you want, you'd like, on a signal, for your program
to
> >go into the background (still running but no longer blocking the terminal
> >input/output). On another signal you would like the program to come back
to
> >the foreground.
> >
> >If this is the case, the problem you're facing is that the program being
in
> >the foreground and the background is actually part of the shell, not a
> >property of the program running.  Most Shells provide a way to switch
> >programs from the foreground to the background and back.
> >BASH for example I could type
> >
> >$>./myprogram
> >(cntr + Z) //suspends the current program and prings the prompt back
> >$>bg  (runs the program in the background)
> >
> >The only way that I know of to force a program to run in the background
in
> >the code is to make it a daemon which is done by forking twice
> >
> >int main(  ) {
> >   if(fork()==0)  {
> >            if( fork() == 0 )  {
> >                    program code starts here
> >             }
> >            exit(0);
> >    }
> >    exit(0);
> >}
> >
> >
> I don't feel it's required to fork() twice for making it a daemon, once
> is enough. Ya, but should use setpgrp() or setpid() and close stdin, out
> and err after the fork and go to infinite loop.
>
> -Raghu
>
> >
> >----- Original Message -----
> >From: "Silambu Chelvan" <silambu_mdu@yahoo.com>
> >To: <linux-newbie@vger.kernel.org>
> >Sent: Monday, September 22, 2003 6:48 AM
> >Subject: Switching between foreground and background
> >
> >
> >
> >
> >>Hi all,
> >>
> >>I have written some program with signal handler. Is
> >>this possible, if
> >>one of the signals registered with my program is
> >>raised, my program
> >>should goto background and should come to foreground
> >>when some other of the
> >>registered signal is raised. how to do it?
> >>
> >>Any function available to switch a process between
> >>foreground and
> >>background at runtime?
> >>
> >>with regards,
> >>M. SilambuChelvan
> >>
> >>
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> >
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