From owner-freebsd-hackers@freebsd.org Fri Mar 3 22:30:45 2017 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 87742CF615C for ; Fri, 3 Mar 2017 22:30:45 +0000 (UTC) (envelope-from freebsd-rwg@pdx.rh.CN85.dnsmgr.net) Received: from pdx.rh.CN85.dnsmgr.net (br1.CN84in.dnsmgr.net [69.59.192.140]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 2170411DF for ; Fri, 3 Mar 2017 22:30:44 +0000 (UTC) (envelope-from freebsd-rwg@pdx.rh.CN85.dnsmgr.net) Received: from pdx.rh.CN85.dnsmgr.net (localhost [127.0.0.1]) by pdx.rh.CN85.dnsmgr.net (8.13.3/8.13.3) with ESMTP id v23MUhpE072956; Fri, 3 Mar 2017 14:30:43 -0800 (PST) (envelope-from freebsd-rwg@pdx.rh.CN85.dnsmgr.net) Received: (from freebsd-rwg@localhost) by pdx.rh.CN85.dnsmgr.net (8.13.3/8.13.3/Submit) id v23MUg5b072955; Fri, 3 Mar 2017 14:30:42 -0800 (PST) (envelope-from freebsd-rwg) From: "Rodney W. Grimes" Message-Id: <201703032230.v23MUg5b072955@pdx.rh.CN85.dnsmgr.net> Subject: Re: kill -0 --- side effect or supported In-Reply-To: <11A4B6AB-E51D-4754-8E80-4503687E0F84@gmail.com> To: "Ngie Cooper (yaneurabeya)" Date: Fri, 3 Mar 2017 14:30:42 -0800 (PST) CC: Dirk-Willem van Gulik , freebsd-hackers@freebsd.org X-Mailer: ELM [version 2.4ME+ PL121h (25)] MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII X-Mailman-Approved-At: Fri, 03 Mar 2017 22:54:17 +0000 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 03 Mar 2017 22:30:45 -0000 -- Start of PGP signed section. [ Charset UTF-8 unsupported, converting... ] > > > On Mar 3, 2017, at 14:12, Dirk-Willem van Gulik wrote: > > > > I regularly use 'kill -0 ' on FreeBSD as a way to test if a certain process is still running (but without actually sending the signal). And I think it has worked reliably since the mid 80's. > > > > Is it actually a properly supported use - as I recently happened to notice that it does not seem to be all that documented in kill( > > It better work. I have code that relies on it :)? > > It does work as you noted, according to truss: > > # sudo truss -ff kill -0 1 2>&1 > ... > 79940: kill(1,0) = 0 (0x0) > ? > # > > As noted in kill(2), this is one of the valid values: > > a group of processes. The sig argument may be one of the signals > specified in sigaction(2) or it may be 0, in which case error checking is ^^^^^^^^^^^^^^^^ That bit of information should be promoted from kill(2) to kill(1) by adding 0 to the list as ?. > performed but no signal is actually sent. This can be used to check the > validity of pid. > > So, the manpage for kill(1) is just lacking in the sense that -0 is supported. > > Cheers! > -Ngie -- End of PGP section, PGP failed! -- Rod Grimes rgrimes@freebsd.org