Date: Fri, 3 Mar 2017 14:42:40 -0800 From: "Ngie Cooper (yaneurabeya)" <yaneurabeya@gmail.com> To: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> Cc: Dirk-Willem van Gulik <dirkx@webweaving.org>, freebsd-hackers@freebsd.org Subject: Re: kill -0 <pid> --- side effect or supported Message-ID: <35C6F2AA-309E-4D58-8191-AB99F0195BEC@gmail.com> In-Reply-To: <201703032230.v23MUg5b072955@pdx.rh.CN85.dnsmgr.net> References: <201703032230.v23MUg5b072955@pdx.rh.CN85.dnsmgr.net>
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> On Mar 3, 2017, at 14:30, Rodney W. Grimes =
<freebsd-rwg@pdx.rh.CN85.dnsmgr.net> wrote:
>=20
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>>=20
>>> 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(
>>=20
>> It better work. I have code that relies on it :)?
>>=20
>> It does work as you noted, according to truss:
>>=20
>> # sudo truss -ff kill -0 1 2>&1
>> ...
>> 79940: kill(1,0) =3D 0 (0x0)
>> ?
>> #
>>=20
>> As noted in kill(2), this is one of the valid values:
>>=20
>> 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
> ^^^^^^^^^^^^^^^^
>=20
> That bit of information should be promoted from kill(2) to kill(1) by
> adding 0 to the list as ?.
Actually=E2=80=A6 it is mentioned in kill(1) =E2=80=94 you just have to =
read between the lines:
-signal_number
A non-negative decimal integer, specifying the signal to be =
sent
instead of the default TERM.
0 is technically a non-negative real number.
It might be a good idea to clarify this point/behavior by pointing to =
kill(2) for the signal behavior/description noted above.
Thanks,
-Ngie
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