Dear bash developers - It is very difficult to overcome the problems caused by the scenario described within this email without something the enclosed "setpgrp <pid> <pgrp>" and "killpg <pgrp> <sig>" bash loadable builtins .
Without them, or options to change signal handling for simple commands, it is too easy to create orphan processes, and too difficult to find a workaround to prevent orphan processes being created, as in the following scenario: 1. An "invoker.sh" process runs a "job.sh" bash script in a separate process which runs a long-running (or non-terminating!) 'Simple Command' (not a shell "Job") (call it "nterm.sh"). 2. After a while, the originator decides that the job has timed-out, and kills its process (the instance of bash running job.sh), and then exits. 3. The "long-command" nterm.sh process is left still running as an orphan, and would become a zombie if it tries to exit. I tested this with lastest bash-4.3.33 and with bash-4.2 . The problem is most shell scripts use just simple commands and not background jobs - changing a large number of scripts to use asynchronous background jobs for every simple command that may potentially not terminate due to for example NFS hangs is not an option. Simple commands will run in their own process groups in interactive mode, or that of the parent in non-interactive mode, and will not be killed when their parent job.sh exits because the parent has no background pid to wait for so cannot wait for them. This is demonstrated by the attached shell scripts in the "nterm-demo.tar" file (nterm-demo/*) : invoker.sh: forks off "job.sh", waits for it to timeout, and kills it job.sh : runs "nterm.sh" as a simple command nterm.sh : a non-terminating process killpg.c : killpg built-in To demonstrate: $ tar -xpf nterm_demo.tar $ cd nterm_demo $ BASH_BUILD_DIR=... BASH_SOURCE_DIR=... make Example output is : gcc -fPIC -O3 -g -I. -I/home/jvasdias/src/3P/bash -I/home/jvasdias/src/3P/bash/lib -I/home/jvasdias/src/3P/bash/builtins -I/home/jvasdias/src/3P/bash/include -I/home/jvasdias/src/3P/bash-4.30-ubuntu -I/home/jvasdias/src/3P/bash-4.30-ubuntu/lib -I/home/jvasdias/src/3P/bash-4.30-ubuntu/builtins -c -o setpgid.o setpgid.c gcc -shared -Wl,-soname,$@ setpgid.o -o setpgid gcc -fPIC -O3 -g -I. -I/home/jvasdias/src/3P/bash -I/home/jvasdias/src/3P/bash/lib -I/home/jvasdias/src/3P/bash/builtins -I/home/jvasdias/src/3P/bash/include -I/home/jvasdias/src/3P/bash-4.30-ubuntu -I/home/jvasdias/src/3P/bash-4.30-ubuntu/lib -I/home/jvasdias/src/3P/bash-4.30-ubuntu/builtins -c -o killpg.o killpg.c ... gcc -shared -Wl,-soname,$@ killpg.o -o killpg bash -c ./invoker.sh 0<&- 2>&1 | tee ./invoker.sh: hB : 11524 JOB: 11528 ./job.sh: 11528: pgid : 11510 ./job.sh: 11528: pgid now : 11528 ./nterm.sh: hB: 11535 : pgid: 11528 non-terminating command 11535 (11528) still running. ./invoker.sh: timeout - killing job: 11528 Terminated ./nterm.sh: 11535: exits 143 ./job.sh: 11528: exits 143 ./invoker.sh: 11524: exiting. $ To demonstrate the problem, make the built-ins not be found: $ make show_the_bug unset BASH_LOADABLES_DIR; ./invoker.sh 0<&- 2>&1 | tee ./invoker.sh: hB : 11670 Demonstrating the bug. Please kill the nterm.sh process manually. JOB: 11672 ./job.sh: 11672: pgid : 11668 job.sh will be killed, but nterm.sh will not. ./nterm.sh: hB: 11676 : pgid: 11668 non-terminating command 11676 (11668) still running. ./invoker.sh: timeout - killing job: 11672 non-terminating command 11676 (11668) still running. non-terminating command 11676 (11668) still running. ^Cmake: *** [show_the_bug] Interrupt Fortunately, make carefully cleans up and kills 11676 silenty. If one types at the command line or in a shell script: $ BASH_LOADABLES_DIR='' ./invoker.sh then it is really hard to kill the resulting nterm.sh process - one has to use kill -9 $nterm_pid . So, please give scripts some means of saying "if I am killed, kill my current simple command", even in interactive mode, with some new shopt option, or provide something like the killpg / setpgid built-ins attached. Thanks & Regards, Jason
nterm_demo.tar
Description: Unix tar archive
