Hi. I've been wrestling recently[1] with a bash script which invokes a number of subprocesses in parallel and collects the output. The problem is that if you ^C the script, the subprocesses carry on running. This is because of the standards-mandated resetting of SIGINT (and QUIT) to SIG_IGN in children.
Working around this in a race-free way with additional code in the script is very hard indeed. I can't see how to do it without having the parent install an INT trap handler which synchronises with all the children, or something equally baroque. The reason for SIGINT being ignored is purely historical: back in the dawn of time, there was no job control. If you interactively spawned a background process with &, you wouldn't want your attempts to ^C your foreground process to kill it. This SIGINT-ignoring also applied to noninteractive shells and of course came to be relied on. So it is too late to change the default :-/. However, it would be very easy for bash to provide an option (via `set -o' perhaps) to disable this behaviour. That is, to allow SIGINT to be delivered normally to child processes. With such an option, scripts which run on modern systems and which attempt to parallelise their work, would be able to arrange that ^C properly cleans up the whole process group, rather than leaving the background tasks running (doing needless work and perhaps causing lossage). I suggest that this option should have two possible modes: 1. Current behaviour (the default): SIGINT and SIGQUIT are set to SIG_IGN in the child shortly after fork. 2. In the child, reset SIGINT and SIGQUIT to the values found at shell startup. That is, uninstall trap handlers. This is what most ordinary scripts will want, because they don't want the trap handler running in both parent and child. It's the same as is done for all other signals, and for all signals in non-background subshells and subprocesses. If this sounds like a good idea, I'm happy to write the patch. Please tell me what these options should be called :-). I suggest: set -o nobgchildsigint # posix behaviour set -o bgchildsigint # reset to shell's inherited dispositions I suggest that these options do the same for both signals. Ie that it wouldn't be possible to specify the inheritance separately for INT and QUIT. This whole discussion, and these proposed options, are relevant only when job control is not in effect. Thanks, Ian. [1] http://lists.xenproject.org/archives/html/xen-devel/2015-10/msg01208.html http://lists.xenproject.org/archives/html/xen-devel/2015-10/msg01211.html