Date: Mon, 25 Nov 2002 18:03:40 +0000 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: freebsd-questions@FreeBSD.ORG Subject: Re: Apache not killing subprocesses, only on FreeBSD Message-ID: <20021125180340.GB44729@happy-idiot-talk.infracaninophi> In-Reply-To: <20021125112037.W39486-100000@duey.wolves.k12.mo.us> References: <DAPNWVLH3Y2YJH5YPXHB4XZWECQKHB.3de075d8@lee> <20021125112037.W39486-100000@duey.wolves.k12.mo.us>
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On Mon, Nov 25, 2002 at 11:23:55AM -0600, Chris Dillon wrote:
> On Sun, 24 Nov 2002, Lee Nelson wrote:
>
> > myprogram.pl reads a few parameters from STDIN, and then
> > forks to work in the background:
> >
> > my $pid = fork;
> > exit if $pid;
> > die ("$pn couldn't fork $!\n") unless defined $pid;
> > POSIX::setsid()
> > or die ("$pn can't start a new session: $!\n");
> >
> > Any clues or suggestions welcome.
>
> The following method to daemonize a PERL process works for me in
> FreeBSD (I don't remember why I fork && exit twice, so don't ask):
>
> require 'sys/syscall.ph';
>
> fork && exit;
> syscall(&SYS_setsid) || die "Can't call setsid(): $!";
> chdir("/");
> open(STDIN, "</dev/null") || die "Can't redirect stdin: $!";
> open(STDOUT, ">/dev/null") || die "Can't redirect stdout: $!";
> open(STDERR, ">/dev/null") || die "Can't redirect stderr: $!";
> fork && exit;
>
The 'double fork' trick ensures that the daemon process gets
re-parented as a child of init(8). As init will reap any child
process that happens to die, this suppresses zombies plus it has
several other effects like dissociating the daemon process from a
controlling terminal. Calling setsid(2) has a similar effect, so you
probably don't need to fork twice and call setsid(2).
The source to the daemon(3) function in /usr/src/lib/libc/gen/daemon.c
is a good example of the canonical way to do that sort of thing.
Cheers,
Matthew
--
Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks
Savill Way
Marlow
Tel: +44 1628 476614 Bucks., SL7 1TH UK
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