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From: oattes@utmanitou.toronto.edu (Lee Oattes)
Newsgroups: comp.unix.wizards
Subject: Re: how do I make a process release its terminal?
Message-ID: <121@utmanitou.toronto.edu>
Date: Thu, 29-Jan-87 17:41:34 EST
Article-I.D.: utmanito.121
Posted: Thu Jan 29 17:41:34 1987
Date-Received: Sat, 31-Jan-87 10:22:35 EST
Expires: Mon, 16-Feb-87 00:00:00 EST
References: <118@lmi-angel.UUCP>
Reply-To: oattes@utmanitou.UUCP (Lee Oattes)
Distribution: na
Organization: Dept. of Astronomy, Scarborough Campus, U. of Toronto, Toronto, Canada.
Lines: 39
Summary: make a process behave like cron

In article <118@lmi-angel.UUCP> wsr@lmi-angel.UUCP (Wolfgang Rupprecht) writes:
>In article <> paul@vixie.UUCP (Paul Vixie Esq) writes:
>>I see that syslogd, inetd, cron, and the rest do NOT show 'co' as their
>>control terminal; how do I make this happen for me?
>
>try this: 
>    if ((f = open ("/dev/tty", 2)) >= 0)
>    {
>	ioctl (f, TIOCNOTTY, 0);
>	close (f);
>    }
>Wolfgang Rupprecht	{harvard|decvax!cca|mit-eddie}!lmi-angel!wsr

To this reply I would add that the following does a more complete job:

#include <sys/ioctl.h>
#include <sys/file.h>

	if( -1 == (fd = open("/dev/tty",O_RDWR)) ){
		fprintf(stderr,"could not open controlling terminal!\n");
		exit(-1);
	}
	if(  -1 == ioctl(fd,TIOCNOTTY,0) ) {
		fprintf(stderr,"could not unlink conrolling terminal!\n");
		exit(-1);
	}
	freopen("/dev/null","r",stdin);
	freopen("/dev/null","w",stdout);
	freopen("/dev/null","w",stderr);

This will remove the process from a "tty" and also close off the
standard connections to that "tty". We use this to run jobs from phone
lines which will continue to run after we log off.  If we do not remove
the job from the phone line "tty" they cause the kernel to think that
(correctly) the device is open and will not allow dialouts thru that
device.

Lee Oattes
{ihnp4!utzoo!, seismo!utai!, decvax!utcsri!, watmath!utai!} utmanitou!oattes