守护进程的两种实现

 1 void daemon()
 2 {
 3     struct rlimit rl;
 4     umask(0);
 5     pid_t pid ;
 6     pid = fork();
 7     if(pid <0 )
 8     {
 9         perror("fork error");
10         return 0;
11     }
12     if(pid > 0) /* parent */
13     {
14         exit(0);
15     }
16     else /* child */
17     {
18         /*
19          * 在关闭描述符之前仍旧可以使用标准输入，标准输出
20          */
21         setsid();
22         getrlimit(RLIMIT_NOFILE,&rl);
23         printf("the max file num is %d: \n",rl.rlim_max);/*setsid()已经与控制终端分离*/
24         printf("the max file num is %d: \n",RLIM_INFINITY);
25         if(rl.rlim_max == RLIM_INFINITY)
26             rl.rlim_max = 1024;
27 
28         int i ;
29         for(i=0; i<rl.rlim_max; i++)
30             close(i);
31         int fd0, fd1, fd2;
32         fd0 = open("/dev/null",O_RDWR);
33         fd1 = dup(0);
34         fd2 = dup(0);
35         openlog("hello", LOG_CONS, LOG_DAEMON);
36     }
37 }

1 #include <unistd.h>
2 
3 int main()
4 {
5     daemon(0,0);
6     while(1){  /*　不会马上结束　*/
7 
8     }
9 }