Date: Fri, 3 Mar 2017 14:30:42 -0800 (PST) From: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> To: "Ngie Cooper (yaneurabeya)" <yaneurabeya@gmail.com> Cc: Dirk-Willem van Gulik <dirkx@webweaving.org>, freebsd-hackers@freebsd.org Subject: Re: kill -0 <pid> --- side effect or supported Message-ID: <201703032230.v23MUg5b072955@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <11A4B6AB-E51D-4754-8E80-4503687E0F84@gmail.com>
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-- Start of PGP signed section. [ Charset UTF-8 unsupported, converting... ] > > > On Mar 3, 2017, at 14:12, Dirk-Willem van Gulik <dirkx@webweaving.org> wrote: > > > > I regularly use 'kill -0 <pid>' 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
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