/* daemon
 * how to create a daemon process?
 * --Just follow these steps.
 *  2014-09-28
 *  zsl
 */
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <fcntl.h>
#define MAXFILE 65536
int main()
{
    pid_t child_pid, new_pid;
    int fd;
    int i;
    child_pid = fork();
    if ( child_pid < 0 )        // fork failed
    {
        perror("fork");
        exit(1);
    }
    else if (child_pid > 0 )    // parent
    {
        fprintf(stderr, "Parent exit...\n");
        exit(0);
    }
    else                        // child
    {
        /* Create a new session */
        new_pid = setsid();
        if ( new_pid < 0)
        {
            perror("setsid");
            exit(1);
        }
        /* Change dir */
        if ( chdir("/") != 0 )
        {
            perror("chdir");
            exit(2);
        }
        /* Set umask */
        umask(0000);
        /* Close all file descriptor */
        for (i = 0; i < MAXFILE; i ++)
        {
            close(i);
        }
        
        /* The daemon job */
        while(1)
        {
            if ((fd = open("/tmp/daemon_log.txt", O_CREAT | O_APPEND | O_WRONLY, 0600)) == -1)
            {
               perror("open"); 
               exit(3);
            }
            write(fd, "daemon is working...\n", 21);
            close (fd);
            sleep(10);
        }
    }   // end of childe process
    return 0;
}