Re: FEATURE REQUEST : shell option to automatically terminate child processes on parent death

[Corto Beau]

Do you mean something like a "fork_noreparent" builtin that would call 
make_child and set PDEATHSIG afterwards, or a "noreparent" builtin that 
the child would have to call ? I do agree that it wouldn't make sense to 
implement the later as a shell option, but this particular use of prctl 
is subject to a race condition that can only be avoided by comparing the 
PID of the parent before calling fork and after calling prctl (in case 
the process got reparented before setting PDEATHSIG), because checking 
for ppid = 1 is not enough on systems like Linux where the process might 
have been reparented by a subreaper.

On 11/11/2023 20:49, Oğuz wrote:
> On Saturday, November 11, 2023, Corto Beau <corto.beau@laposte.net> wrote:
>
>     Configuration Information [Automatically generated, do not change]:
>     Machine: x86_64
>     OS: linux-gnu
>     Compiler: gcc
>     Compilation CFLAGS: -g -O2
>     uname output: Linux zinc 6.6.1-arch1-1 #1 SMP PREEMPT_DYNAMIC Wed,
>     08 Nov 2023 16:05:38 +0000 x86_64 GNU/Linux
>     Machine Type: x86_64-pc-linux-gnu
>
>     Bash Version: 5.2 Patch
>     Level: 21
>     Release Status: release
>
>     Description:
>     Hi,
>
>     I would like to suggest a new shell option to ensure child
>     processes are automatically killed when the parent dies.
>
>     Right now, it's already possible to emulate this feature by
>     setting a trap to kill all child processes on exit (trap "kill 0"
>     EXIT), but obviously it doesn't work if the process is terminated
>     by a signal that cannot be caught (like SIGKILL).
>
>     On Linux, it can be done by setting the PR_SET_PDEATHSIG flag to
>     propagate the parent termination signal to the child, regardless
>     of whether the signal can be caught or not.
>
>     The rationale for this feature is that scripts spawning background
>     processes to listen to various events (udev events, window manager
>     events, etc) often leave orphan processes behind when terminated
>     forcefully.
>
>     I've attached a proof-of-concept patch.
>
>
> I think it'd make more sense to implement this as a loadable builtin.
>
>
> --
> Oğuz