/* closeall() - close all FDs >= specified value */
void closeall(int fd)
{
 int fdlimit = sysconf(_SC_OPEN_MAX);
 while ( fd < fdlimit )
  close(fd++);
}

/* daemon() - detach process from user and disappear into the background */
int daemon(int nochdir, int noclose)
{
 switch ( fork() )
 {
     case 0:
       break;
     case -1:
       return -1;
     default:
       exit(0);  /* exit the original process */
 }

 /* create new session not having controlling terminal */
 if (setsid() < 0)    /* shoudn't fail */
    return -1;

 /* now we aren't session group leader, so never gain controlling terminal */
 switch ( fork() )
 {
    case 0:
      break;
    case -1:
      return -1;
    default:
      exit(0);
 }

 /* here run the child */
 if ( !nochdir )
  chdir("/");

 if ( !noclose ) {
  closeall(0);
  open("/dev/null", O_RDWR);
  dup(0); dup(0);
 }

 return 0;
}

...

int main(void)
{
  .....
     if ( daemon(0, 0) < 0 ) {
           perror("daemon");
           exit(2);
     }

     process();     /* run main process */

     return 0;
}

     process();     /* run main process */
}