How to kill a zombie process in Linux?

superfluous

When parent cannot handle the exited child process, the child process becomes a zombie, also known as a defunct process. The defunct process uses a little resource. It cannot be killed by kill(). It exists in all the system life. Then how to kill a zombie process? There are several ways to kill a zombie process or avoid to generate a zombie process as follows:
1. Kill the parent to eliminate the zombie processes
2. Wait a child to exit through calling wait() to avoid to generate a zombile process
3. Ignore the SIGCHLD signal (in Linux 2.6 but 2.4; POSIX-2001) to avoid to generate a zombie process
It should be noted that a zombie process is defunct so that any kill() or related command cannot affect it.
example 1: Call signal() to avoid to generate a zombie process
           The main process(parent process) is not blocked
...
signal(SIGCHLD, SIG_IGN);
...
if ((pid = fork()) == -1){
  ...
}
else if (!pid) {
  ...
  exit(0);
}
...
$kill -9 {CHILD}
$ps x
/* child not ba a zombie */
example 2: Call wait() to avoid to generate a zombie process
           The main process(parent process) is blocked
...
if ((pid = fork()) == -1){
  ...
}
else if (!pid) {
  ...
  exit(0);
}
wait(&child_exit_status);
...
$kill -9 {CHILD}
$ps x
/* child not ba a zombie */
               
               
               

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