From owner-freebsd-rc@FreeBSD.ORG Sat Jul 17 23:10:01 2010 Return-Path: Delivered-To: rc@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 350F9106566B for ; Sat, 17 Jul 2010 23:10:01 +0000 (UTC) (envelope-from jhellenthal@gmail.com) Received: from mail-iw0-f182.google.com (mail-iw0-f182.google.com [209.85.214.182]) by mx1.freebsd.org (Postfix) with ESMTP id E32EE8FC1B for ; Sat, 17 Jul 2010 23:10:00 +0000 (UTC) Received: by iwn35 with SMTP id 35so4236425iwn.13 for ; Sat, 17 Jul 2010 16:10:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:sender:date:from:to:cc :subject:in-reply-to:message-id:references:user-agent :x-openpgp-key-id:x-openpgp-key-fingerprint:mime-version :content-type; bh=acYRNXgtgKTOidiLZ/b9lPms7A3qKG4AwOHyeB9mc6U=; b=YLITH9SgU2XdTSYXplQw9jTyDbYaJsYjN/u14FcJJhOw2+O/50Cb9cmMz6RoTJT2DP vxVlVX6oTwEW/viZPBJ108h3Q1c8wh3b/kjSH59ro0SF1rpUPAep8yvTAnTHmVqDEjS9 YRVCSa1ISnUQWELmHs0iJjJfLpbPw6rwqBdy8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:x-openpgp-key-id:x-openpgp-key-fingerprint:mime-version :content-type; b=epzTnkHK0qkwaItbVwVAGbKFc8jRD9cDsS6KOM2bsrhucbK407nZjeIVksj9TzOpAb Mgi4GGjrVAw/L8jX49umaqQUeUWSG3pW/Y+ytsUnKmw5+gHwaOehHpUxuchmoovgoup9 40BOL0zk4gJjjQwDXZCxo/7t+bTganKIODDPk= Received: by 10.231.79.212 with SMTP id q20mr3088629ibk.103.1279406594940; Sat, 17 Jul 2010 15:43:14 -0700 (PDT) Received: from centel.dataix.local ([99.181.132.254]) by mx.google.com with ESMTPS id g31sm16800368ibh.16.2010.07.17.15.43.13 (version=TLSv1/SSLv3 cipher=RC4-MD5); Sat, 17 Jul 2010 15:43:14 -0700 (PDT) Sender: "J. Hellenthal" Date: Sat, 17 Jul 2010 18:43:07 -0400 From: jhell To: Ed Schouten In-Reply-To: <20100717105658.GV1742@hoeg.nl> Message-ID: References: <20100717105658.GV1742@hoeg.nl> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) X-OpenPGP-Key-Id: 0x89D8547E X-OpenPGP-Key-Fingerprint: 85EF E26B 07BB 3777 76BE B12A 9057 8789 89D8 547E MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: ports@freebsd.org, rc@freebsd.org Subject: Re: General note on rc scripts and daemonizing X-BeenThere: freebsd-rc@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Discussion related to /etc/rc.d design and implementation." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 17 Jul 2010 23:10:01 -0000 On Sat, 17 Jul 2010 06:56, Ed Schouten wrote: In Message-Id: <20100717105658.GV1742@hoeg.nl> > Hello port maintainers, > > I think I'd better send an email about this to ports@, because I've seen > it in various places and it is getting a bit tiresome to mail all port > authors individually. > > I've seen various cases in the past where people write rc scripts that > do the following: > > command="/usr/local/bin/dog" > command_args="--bark > /dev/null 2>&1 &" > > So in this case `dog --bark' doesn't daemonize itself, so the & is > sufficient here, right? Well, it is not. :-) The point is that we simply > tell the kernel to redirect stdout/stderr and run it in the background. > It doesn't tell the kernel that the process should run in a separate > session (see getsid(2)/setsid(2)). > > This has various implications. The most important one I can think of, is > that the daemon can still do open("/dev/tty", ...) if it wants and spam > your TTY, even if the daemon is running as user `nobody'. This also > means that if you run the rc script from within a pseudo-terminal, it > can never actually destroy the pseudo-terminal for you, because maybe > the daemon is interested in using it. > > Below is the output of `pstat -t' on one of my systems, where I decided > to fire up MySQL: > > | LINE INQ CAN LIN LOW OUTQ USE LOW COL SESS PGID STATE > | ... > | pts/11 0 0 0 0 0 0 0 0 82711 0 G > > The kernel actually wants to clean up this pseudo-terminal (state = G), > but it is prevented from doing so. It will only clean it up by the time > MySQL is shut down. > > So how can this be solved? We already have a tool in base called > daemon(8). It is simply a wrapper around daemon(3) (which calls > setsid(2), which you can use to daemonize processes. So the next time > you write an rc script and need to daemonize something which cannot do > it by itself, please think of the kittens. ;-) > > [ CCing this to rc@. Maybe we should add some kind of built-in > functionality to call daemon(8)? ] > Hi Ed, Very nice note as well a very good practice. I have noticed this for a while but never looked into it more so I could not really put a name to it. Thanks. Off topic of ports: While this subject is hot, I have been doing the following on an updated system, current version of xterm on two up-to-date stable/8 machines. I am having trouble narrowing down the cause of the controlling pseudo terminal freezing until ^C is hit after using daemon(1) to spawn ssh in the background to start a remote xterm. # Open a pseudo terminal [pts/13] xterm (the culprit) # Mix up the terminal a little so its not so fresh. [pts/13] ls -l # Use daemon to start a remote xterm through ssh. [pts/13] daemon ssh -M remotehost xterm At this stage the remote x11 forwarded xterm opens and works properly "set this terminal aside, its not the problem". # On the originating pseudo terminal [pts/13] su - Password: ********** host# _ After that you should have to hit ^C to proceed to the next bang line or enter anything for that matter. Any clue at what might be going on or any more information that I could provide to help deduce this ?. Regards, -- jhell,v