Date: Fri, 25 Mar 2022 12:13:27 -0700 From: Bryan Drewery <bdrewery@FreeBSD.org> To: Ganael Laplanche <ganael.laplanche@martymac.org>, freebsd-hackers@freebsd.org Subject: Re: Our /bin/sh and process group IDs Message-ID: <243ebc92-26a1-e5e7-67fe-1477ed6b5f7a@FreeBSD.org> In-Reply-To: <48e49ad0-a12a-d10b-5867-da9736c6c1fd@martymac.org> References: <48e49ad0-a12a-d10b-5867-da9736c6c1fd@martymac.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 3/24/2022 10:13 AM, Ganael Laplanche wrote:
> Hello,
>
> I am trying to fork a sub-shell with its own process group id through a
> function that must itself be executed in the background.
>
> It should work with the following code:
>
> #----
> #!/bin/sh
>
> # Parent shell IDs
> ps -o pid,ppid,pgid,comm -p $$
>
> test_func () {
> set -m
> { /bin/sh -c 'sleep 1' ; } &
> # Forked shell IDs (pgid should be different from parent,
> # but it is not)
> ps -o pid,ppid,pgid,comm -p $!
set -m needs to be set from the parent process, not child. In this
example test_func is a child *and* the sleep is a child which is also
very racy. Here's a pattern I use that works:
#! /bin/sh
ps -o pid,ppid,pgid,comm -p $$
test_func() {
mypid=$(sh -c 'echo $PPID')
ps -o pid,ppid,pgid,comm -p $mypid
}
spawn() {
local - # cause -m to revert back on return
set -m
"$@" &
}
spawn test_func
ps -o pid,ppid,pgid,comm -p $!
> }
>
> # The following does not work:
> test_func &
> # ...but it works when function is not executed in the background:
> #test_func
>
> sleep 2
> exit 0
> #----
>
> Unfortunately, with our /bin/sh, the sleeping process gets the *same*
> process group ID as its parent.
>
> I've tested several shell implementations; it works with :
>
> /usr/local/bin/bash --posix 'test.sh' # from bash-5.1.16
> /usr/local/bin/zsh --emulate sh 'test.sh' # from zsh-5.8.1
> /usr/local/bin/ksh93 'test.sh' # from ksh93-devel-2020.06.30
> /usr/local/bin/mksh 'test.sh' # from mksh-59c
> /usr/local/bin/ksh 'test.sh' # from pdksh-5.2.14p2_6
>
> but not with :
>
> /bin/sh 'test.sh' # on 13.0-RELEASE-p8
> /usr/local/bin/dash 'test.sh' # from dash-0.5.11.5
>
> am I missing something ?
>
> Any help welcome :)
>
> Best regards,
>
--
Bryan Drewery
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?243ebc92-26a1-e5e7-67fe-1477ed6b5f7a>