守护进程

# 终端

 # 进程组

# 会话

# 守护进程

// 创建一个会话，每隔2s获取系统时间，并将时间写入到磁盘文件中

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/time.h>
#include <signal.h>
#include <time.h>
#include <string.h>

void handle(int num)
{

    time_t present_time = time(NULL);
    struct tm *loc = localtime(&present_time);
    // char buf[1024];
    // sprintf(buf, "%d-%d-%d %d:%d:%d\n", loc->tm_year, loc->tm_mon, loc->tm_mday,
    // loc->tm_hour, loc->tm_min, loc->tm_sec);



    // printf("%s\n", buf);
    int a_fd = open("/home/Linux/lesson22/a.txt", O_RDWR | O_CREAT | O_APPEND, 0777);
    write(a_fd, buf, strlen(buf));
    close(a_fd);

}


int main()
{
    // 创建子进程
    pid_t pid = fork();

    // 父进程退出
    if(pid > 0)
    {
        exit(0);
    }

    // 子进程创建会话
    setsid();
    //更改工作目录
    chdir("/");
    // 关闭、重定向文件描述符
    int fd = open("/dev/null", O_RDWR);

    dup2(fd, STDIN_FILENO);
    dup2(fd, STDOUT_FILENO);
    dup2(fd, STDERR_FILENO);

    struct sigaction act;
    act.sa_handler = &handle;
    act.sa_flags = 0;
    sigemptyset(&act.sa_mask);

    sigaction(SIGALRM, &act, NULL);




    struct itimerval new_value;
    new_value.it_interval.tv_sec = 2;
    new_value.it_interval.tv_usec = 0;
    new_value.it_value.tv_sec = 2;
    new_value.it_value.tv_usec = 0;


    setitimer(ITIMER_REAL, &new_value, NULL);

    while(1)
    {
        sleep(10);
    }






    return 0;
}