Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!think.com!snorkelwacker.mit.edu!bloom-beacon!eru!hagbard!sunic!erbe.se!prc
From: prc@erbe.se (Robert Claeson)
Newsgroups: comp.unix.questions
Subject: Re: Starting a daemon on a SVR3
Message-ID: <1991Jan7.120329.787@erbe.se>
Date: 7 Jan 91 12:03:29 GMT
References: <25360@adm.brl.mil>
Organization: ERBE DATA AB, Jakobsberg, Sweden
Lines: 47

In article <25360@adm.brl.mil> wolf@grasp1.univ-lyon1.fr writes:

>On an old AIX, I use following code to start a daemon (which does not run
>with root privileges).

[Source code deleted.]

>   setbuf(stdout,NULL); printf("Listserv v0.99: daemon started\n\r");
>   if (fork()) exit (0);   /* Dissociate us from tty */
>   for (i=getdtablesize()-1; i>=0; i--)
>      (void)close(i);
>   (void)open("/",0);
>   (void)dup2(0,1);
>   (void)dup2(0,2);
>   i=open("/dev/tty",2);
>   if (i>=0) {
>      ioctl(i,TIOCNOTTY,(char *)0);
>      (void)close(i);
>   }

>This works fine, but I get trouble when porting this daemon to an SRV3.
>getdtablesize does not exist anymore, so I close all open files manually
>with a fixed loop (I put 4 in first index).

>The ioctl call does also not exist, and I found no equivalence.
>After having executed the new code it loads itself in background and
>ps shows me it does not depend anymore on a tty.  Despite this, when
>I loggoff, the process is being killed.  Can anyone explain me what I
>have to do to start properly a daemon?  Thanx.

I believe that something along these lines should work:

	setbuf(stdout,NULL);
	printf("Listserv v0.99: daemon started\n\r");
	if (fork())		/* Disaccociate us from controlling tty */
		exit(0);
	setpgrp();		/* Start a new process group */
	if (fork())		/* ...and disaccociate us again */
		exit(0);

I only have a vague memory of why the second fork() is needed.

-- 
Robert Claeson                  |Reasonable mailers: rclaeson@erbe.se
ERBE DATA AB                    |      Dumb mailers: rclaeson%erbe.se@sunet.se
Jakobsberg, Sweden              |  Perverse mailers: rclaeson%erbe.se@encore.com
Any opinions expressed herein definitely belongs to me and not to my employer.