daemon basics

daemon.txt

// http://www.crankyotaku.com/2016/04/linux-programming-daemon-basics.html

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

int main(int argc, char *argv[])
{
	int maxfd, fd;

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

	if(setsid() == -1){
		printf("Error becoming session leader\n");
		_exit(EXIT_FAILURE);
	}

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

	umask(0);
	chdir("/");
	maxfd = sysconf(_SC_OPEN_MAX);
	for(fd = 0; fd < maxfd; fd++)
		close(fd);

	close(STDIN_FILENO);
	fd = open("/dev/null", O_RDRW);
	if(fd != STDIN_FILENO)
		_exit(EXIT_FAILURE);

	if(dup2(STDIN_FILENO, STDOUT_FILENO) != STDOUT_FILENO)
		_exit(EXIT_FAILURE);

	if(dup2(STDIN_FILENO, STDERR_FILENO) != STDERR_FILENO)
		_exit(EXIT_FAILURE);

	for(;;){
		//This daemon will run forever. use ps aux | grep ./[name of program] to
		//find it and kill it. If you don't care to observe its
		//properties while its running remove the endless for loop.
	}
}