killing Parent process along with child process using SIGKILL
When you kill a process alone, it will not kill the children.
You have to send the signal to the process group if you want all processes for a given group to receive the signal.
kill -9 -parentpidOtherwise, orphans will be linked to init.
Child can ask kernel to deliver SIGHUP (or other signal) when parent dies by specifying option PR_SET_PDEATHSIG in prctl() syscall like this:
prctl(PR_SET_PDEATHSIG, SIGHUP);See man 2 prctl for details.
Sending the -9 signal (SIGKILL) to a program gives no chance for it to execute its own signal handlers (e.g., your trap statements). That is why the children don't get killed automatically. (In general, -9 gives no chance for the app to clean up after itself.) You have to use a weaker signal to kill it (such as SIGTERM.)
See man 7 signal for details.