Re: bash passes changed termios to backgrounded process(es) groups?

[Chet Ramey]

On 8/29/24 4:59 PM, Martin D Kealey wrote:
> On Fri, 30 Aug 2024 at 04:17, Robert Elz <kre@munnari.oz.au 
> <mailto:kre@munnari.oz.au>> wrote:
>
>     SIGTTOU is also sent, unconditionally, by any attempt to change any of
>     the terminal's attributes, and the process (group) (by default) stops.
>     (I don't recall off hand whether simply fetching the attributes is
>     enough to generate SIGTTOU.)   Just as there's no stty option to avoid
>     SIGTTIN (reading from the terminal) there's no option to avoid this
>     kind of SIGTTOU - or there shouldn't be.
>
>
> I've encountered something related to this, where the shell takes charge of 
> the terminal, away from another process that is using it.
>
> This happens when trying to debug a modified version of Bash, with "gdb ./ 
> bash" then "run".
> Gdb then stops twice before Bash prints its prompt, even though Bash 
> doesn't (seem to) print or read anything.

Most likely, bash can't make itself a process group leader to perform job
control. It will try a number of times, then give up and turn job control
off. Since gdb catches all signals sent to the target process, it reacts.
Look at jobs.c:initialize_job_control().

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/

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