kill -s SIGTERM kills parent process and one level child process only-CodePudding

I've been doing some experimenting with writing a command to kill parent and all it's children recursively. I've a script as below

parent.sh:

#!/bin/bash
/home/oracle/child.sh &
sleep infinity

child.sh:

#!/bin/bash
sleep infinity

Started command using

su oracle -c parent.sh &

I see a process tree like below

[root@source ~]# ps -ef | grep "/home/oracle"
root     14129  1171  0 12:39 pts/1    00:00:00 su oracle -c /home/oracle/parent.sh
oracle   14130 14129  0 12:39 ?        00:00:00 /bin/bash /home/oracle/parent.sh
oracle   14131 14130  0 12:39 ?        00:00:00 /bin/bash /home/oracle/child.sh

When I send sigterm to 14129 using kill -s SIGTERM 14129 it appears to kill 14129 and then 14130 goes down as well immediately; but 14131 stays up for a very long time. The last level child appears to have been reparented and has become a zombie.

oracle   14131     1  0 12:39 ?        00:00:00 /bin/bash /home/oracle/child.sh

If kill doesn't terminate any child processes why did 14130 get killed when I sent a SIGTERM to 14129?
If kill can kill child processes, why would does it go only one level down? Is the behavior here guaranteed?

CodePudding user response：

The relevant part of what pilcrow provided is this:

SIGNALS top

   Upon receiving either SIGINT, SIGQUIT or SIGTERM, su terminates
   its child and afterwards terminates itself with the received
   signal. 

   >> The child is terminated by SIGTERM, 
   >> (then) after unsuccessful attempt (to kill with SIGTERM) and 
   >> (after) 2 seconds of delay (,) the child is (then) killed 
   >> by SIGKILL [a second, harsher method].

That harsher method, SIGKILL, prevents that child process from attempting to kill its own children, hence the zombie state.

I haven't used it myself, but it seems that something like

killall --process-group parent.sh

would kill all processes tied to the process group associated with the "parent.sh" script. BUT ... not sure if "--wait" will serve you well, if the method used in the attempt to terminate is not being accepted.