daemon 예제

linux system programming, 174p 예제 실행.

#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/fs.h>

int main (void)

{
	pid_t pid, sid;
	int i;
	int j=0;
	/* create new process */
	pid = fork ();
	printf("Pid is %d \n",pid);
	if (pid == -1)
		return -1;
	else if (pid != 0)
		exit (EXIT_SUCCESS);


	/* create new session */
	sid =setsid();
	if (sid == -1)
		return -1;

	printf("sid is %d \n",sid);
	/* set the working directory to the root directory */
	if (chdir("/") == -1){
		printf("check");
		return -1;
	}

	/* close all open files--NR_OPEN is overkill, but works */
	printf("FOPEN_MAX is %d\n",FOPEN_MAX);
	for (i = 0; i < FOPEN_MAX; i++){
		//j=close(i);
		close(i);
		//printf("%d\n", j);
		printf("%d is closed\n", i);
	}

	/* redirect fd's 0,1,2 to /dev/null */
	open("/dev/null", O_RDWR); /* stdin */
	dup(0); /* stdout */
	dup(0); /* stderror */
	/* do its daemon thing... */

	while(1){

		sleep(1);
		//printf("this is test\n");
	}

	return 0;

}

54번 행 printf가 나오지 않음은 stdout을 죽여서 그런 듯 하다.

NR_OPEN을 찾을 수 없는데, 옛날 프로그램이라 다른 문구로 정의된 듯 하다. FOPEN_MAX로 일단 했다.

pi@raspberrypi:~/Project/cCode/systemProgram $ gcc daemon.c ;./a.out;ps aux | grep pi;
Pid is 1939 
Pid is 0 
sid is 1939 
FOPEN_MAX is 16
0 is closed
message+   346  0.0  0.0   6736  3524 ?        Ss    6월22   0:04 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
avahi      350  0.0  0.0   5896  2960 ?        Ss    6월22   0:02 avahi-daemon: running [raspberrypi.local]
pi         846  0.0  0.1  14716  7204 ?        Ss    6월22   0:12 /lib/systemd/systemd --user
pi         849  0.0  0.0  16864  1772 ?        S     6월22   0:00 (sd-pam)
pi         891  0.0  0.0   7256  3568 tty1     S+    6월22   0:00 -bash
pi        1939  0.0  0.0   1852    64 ?        Ss   19:01   0:00 ./a.out
pi        1940  0.0  0.0   8552  2532 pts/1    R+   19:01   0:00 ps aux
pi        1941  0.0  0.0   6116   496 pts/1    S+   19:01   0:00 grep --color=auto pi
root     28022  0.0  0.1  12236  6304 ?        Ss   17:16   0:00 sshd: pi [priv]
pi       28033  0.0  0.0  12236  3532 ?        S    17:16   0:01 sshd: pi@pts/0
pi       28036  0.0  0.0   7392  3856 pts/0    Ss   17:16   0:00 -bash
pi       28244  0.1  0.1  11564  6728 pts/0    S+   17:19   0:06 vi daemon.c
root     28246  0.0  0.1  12236  6252 ?        Ss   17:19   0:00 sshd: pi [priv]
pi       28257  0.0  0.0  12236  3552 ?        S    17:19   0:00 sshd: pi@pts/1
pi       28260  0.0  0.0   7548  3924 pts/1    Ss   17:19   0:00 -bash

pid 1939가 ?로 대몬으로 변신했다.