用代码实现让程序在后台运行

 

/*------------- daemon.c -----------*/
/*
    说明：让程序自动在后台运行

    cc -o daemon daemon.c
 */

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>

int daemon(int nochdir, int noclose);

int main(int argc, char** argv)
{
    int c;
    bool daemonize = false;
    int maxcore = 0;
    int verbose = 0;

    /* set stderr non-buffering (for running under, say, daemontools) */
    setbuf(stderr, NULL);

    /* process arguments */
    while ((c = getopt(argc, argv, "dc:v")) != -1) {
        switch (c) {
        case 'd':
     daemonize = true;
     break;
     case 'c':
            maxcore = atoi(optarg);
            break;
        case 'v':
            verbose = 1;
            break;
     default:
            fprintf(stderr, "Illegal argument \"%c\"\n", c);
            return 1;
        }
    }

    /* daemonize if requested */
    /* if we want to ensure our ability to dump core, don't chdir to / */
    if (daemonize) {
        int res;
        res = daemon(maxcore, verbose);
        if (res == -1) {
            fprintf(stderr, "failed to daemon() in order to daemonize\n");
            return 1;
        }
    }

       int i = 100;
       while(i--)
       {
           sleep(2);
           fprintf(stdout,"%d ......\n", i);
       }

    return 0;
}

int daemon(int nochdir, int noclose)
{
    int fd;

    switch (fork()) {
    case -1:
        return (-1);
    case 0:
        break;
    default:
        _exit(EXIT_SUCCESS);
    }

    if (setsid() == -1)
        return (-1);

    if (nochdir == 0) {
        if(chdir("/") != 0) {
            perror("chdir");
            return (-1);
        }
    }

    if (noclose == 0 && (fd = open("/dev/null", O_RDWR, 0)) != -1) {
        if(dup2(fd, STDIN_FILENO) < 0) {
            perror("dup2 stdin");
            return (-1);
        }
        if(dup2(fd, STDOUT_FILENO) < 0) {
            perror("dup2 stdout");
            return (-1);
        }
        if(dup2(fd, STDERR_FILENO) < 0) {
            perror("dup2 stderr");
            return (-1);
        }

        if (fd > STDERR_FILENO) {
            if(close(fd) < 0) {
                perror("close");
                return (-1);
            }
        }
    }
    return (0);
}