operating system - How to avoid zombie processes? and what exactly init process does in this situation? -

how avoid zombie processes? , init process in situation?
i've seen program,but not able it: how program creates zombie process:

#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h>  int main(void)  {     pid_t p = fork();      if (p != 0)      {         waitpid(p, null, 0); /* see if child had ended. */         sleep(1); /* wait 1 seconds child end. , eat away sigchld in case if arrived. */         pause(); /* suspend main task. */     }     else     {         sleep(3); /* let child live tme before becoming zombie. */     }      return 0; } 

a child process turns zombie process when did exit parent process did not yet run waitpid, wait or waitid on it. in normal situation parent want know exit status on child process spawned , therefore woud run waitpid on pid got fork.

what happens in code above:

• the child spawned , exits (leaves else clause , returns 0)
• the parent runs endless pause loop until press ctrl-c (the sleep , waitpid superflous)

if start program , leave running (./a.out &) , run ps -fx see this:

 6940 pts/1    sn     0:00      ./a.out  6943 pts/1    zn     0:00       \_ [a.out] <defunct> 

now, if kill parent process (kill 6940) child becomes orphan , init process automatically becomes new parent. since init process runs waitpid (aka "reaps" child) on processes inherits zombie process deleted process table , not show more via ps -f