Linux 守护进程

解释来自https://blog.csdn.net/JMW1407/article/details/108412836

/*
    守护进程
    每隔两秒过去一下系统时间，将这个时间写入到磁盘文件
*/
 
#include 
#include 
#include 
#include 
#include 
#include 
#include
#include 
#include 
#include 
 
void work() {
    time_t tm = time(NULL);
    struct tm *loc = localtime(&tm);
    // 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);
    char * str = asctime(loc);
    int fd = open("time.txt", O_RDWR | O_CREAT | O_APPEND, 0664);
    write(fd, str, strlen(str));
}
 
 
int main() {
    pid_t pid = fork();
    if(pid > 0) {
        exit(0);
    } 
 
    //讲子进程创建一个会话
    setsid();
    
    //设置掩码
    umask(022);
 
    //更改工作目录
    chdir("/home/xiaowu/");
 
    //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_flags = 0;
    act.sa_handler = work;
    sigemptyset(&act.sa_mask);
    
    sigaction(SIGALRM, &act, NULL);
 
    struct itimerval val;
    val.it_value.tv_sec = 2;
    val.it_value.tv_usec = 0;
    val.it_interval.tv_sec = 2;
    val.it_interval.tv_usec = 0;
 
    setitimer(ITIMER_REAL, &val, NULL);
    while(1) {
    }
}