deamon.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void deamonize() {
	if (fork())
		exit(0);	// exit parent process
	setsid();	// become session leader, discard controlling terminal
	signal(SIGINT, SIG_IGN);
	signal(SIGCHLD, SIG_IGN);
	signal(SIGHUP, SIG_IGN);
	signal(SIGQUIT, SIG_IGN);
	signal(SIGPIPE, SIG_IGN);
	if (fork())
		exit(0);	// no more session leader, cannot reopen a contorl terminal
	for (int i = 0; i < 3; ++i)
		close(i);	// close file dscriptor
	chdir("/");
	umask(0);
}

int main() {
	deamonize();
	return 0;
}