fork倆次以避免僵死程序

如果你想讓一個程序fork一個子程序，單不要它等待子程序終止，也不希望子程序處于将死狀态直到父程序終止，通過fork倆次就可以讓 init 程序接管你的程序

#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

 int 
 main(void)
 {
    pid_t pid;

    printf("current pid = %ld\n", (long)getpid());

    if ((pid = fork()) < ) {
        printf("fork errot ");
    } else if (pid == )    {  /* first child */
        if ((pid = fork()) <  )  /* second child */
            printf("fork errot ");
        else if (pid >  ) {
            printf("exit pid = %ld\n", (long)getpid());
            exit(); /* end the parent of the first child */
        }   
        /*
         * We're the scond child;our parent becomes init as soon 
         * as our real parent calls exit() in the statement above.
         * Here's where we'd continue executing, knowing that when
         * we're done, init will reap our status.
        sleep();
        printf("scond child , parent pid = %ld\n", (long)getppid());
        exit();
     }   

     if (waitpid(pid, NULL, ) != pid)
        printf("waitpid error\n");

     exit();   
}     
           

檢視程序是否是init 程序

ps aux | grep 
  是我最後在shell 輸出的 parent pid  ，我原來以為會是程序 呢，結果不是
 我檢視了  發現它也是一個init 程序，是以如果你輸出的不是 那就自己檢視一下
 是否是init 程序。