Date: Fri, 3 Mar 2017 14:23:37 -0800 From: "Ngie Cooper (yaneurabeya)" <yaneurabeya@gmail.com> To: Dirk-Willem van Gulik <dirkx@webweaving.org> Cc: freebsd-hackers@freebsd.org Subject: Re: kill -0 <pid> --- side effect or supported Message-ID: <11A4B6AB-E51D-4754-8E80-4503687E0F84@gmail.com> In-Reply-To: <23F3BAC3-0D8B-4290-8DC2-818D67A0B6A9@webweaving.org> References: <23F3BAC3-0D8B-4290-8DC2-818D67A0B6A9@webweaving.org>
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> On Mar 3, 2017, at 14:12, Dirk-Willem van Gulik <dirkx@webweaving.org> =
wrote:
>=20
> 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.
>=20
> 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 :)=E2=80=A6
It does work as you noted, according to truss:
# sudo truss -ff kill -0 1 2>&1
...
79940: kill(1,0) =3D 0 (0x0)
=E2=80=A6
#
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
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
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