进程的调度与使用

本程序通过创建新进程，使用fork()函数调用，然后用exec调用让进程去加载，子进程中通过execl函数输入命令(date)的路径 （path）,输出当前日期时间。

/* Program that shows how fork system call works */

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

int main(void)
{
    pid_t pid;

    printf("There is only one process now.\n");

    if ((pid = fork()) < 0)  /*子进程创建失败时退出*/
    {
        perror("fork error");
        exit(1);
    }

    if (0 == pid)
    {
      /* Now we are in the child process */

        printf("This message is printed by the child process.\n");
        execl("/bin/date", "date", (char *) 0);
        perror("execl() failure!\n\n");
    } 
    else
    {
      /* Now we are in the parent process*/

            printf("PARENT PROCESS.\n");
    }
    printf("=== The End ===\n");

    return 0;
}