/*
 * UNIX Damon Server Programming Sample Program
 * To compile:		cc -o exampled exampled.c
 * TO run:		./exampled
 * To test daemon: 	ps aux | grep exampled
 * To test log:		tail -f /tmp/exampled.log
 * To test signal:	kill -HUP `cat /tmp/exampled.lock`
 * To terminate:	kill `cat /tmp/exampled.lock`
 */

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>

#define RUNNING_DIR	"/tmp"
#define LOCK_FILE	"exampled.lock"
#define LOG_FILE	"exampled.log"
static const char *months[] = {
	"Jan","Feb","Mar","Apr","May","Jun",
	"Jul","Aug","Sep","Oct","Nov","Dec"};

void log_message(char *filename, char *message)
{
	FILE *logfile;
	char buf[30];
	long n = time(NULL);
	struct tm *now;
	now = localtime(&n);

	sprintf(buf, "%02d:%02d:%02d %s %02d %02d", 
		now->tm_hour, now->tm_min, now->tm_sec,months[now->tm_mon],
		now->tm_mday,now->tm_year % 100);
	
	logfile = fopen(filename, "a");
	if (!logfile) 
		return;
	fprintf(logfile, "%s: %s\n", buf, message);
	fclose(logfile);
}

void signal_handler(int sig)
{
	switch(sig) {
	case SIGHUP:
		log_message(LOG_FILE, "hangup signal catched");
		break;
	case SIGTERM:
		log_message(LOG_FILE, "terminate signal catched...exiting");
		unlink(LOCK_FILE);
		exit(0);
		break;
	}
}

void daemonize()
{
	int i, lfp;
	char str[10];
	
	if (getppid() == 1) /* already a daemon */
		return;
		
	i=fork();
	
	if (i<0) /* fork error */
		exit(1);
	if (i>0) /* parent exits */
		exit(0);
	/* child daemon continues */
	
	setsid(); /* obtain a new process group */
	
	for (i=getdtablesize(); i>=0; --i)
		close(i); /*close all descriptors*/
		
	i=open("/dev/null", O_RDWR); /* handle std. io */
	dup(i);
	dup(i);
	
	umask(027); /* set newly created file permissions */
	
	chdir(RUNNING_DIR); /* change running directory*/
	
	//attempt to create lockfile and put a file-lock on it
	lfp=open(LOCK_FILE,O_RDWR|O_CREAT, 0640);
	if (lfp<0) /* can not open */
		exit(1);
	if (lockf(lfp,F_TLOCK,0) < 0) /* can not lock */
		exit(0);
	
	/* first instance continues */
	sprintf(str, "%d\n", getpid() ); /* record pid to lockfile */
	write(lfp, str, strlen(str) );
	signal(SIGCHLD, SIG_IGN); /* ignore child */
	signal(SIGTSTP, SIG_IGN); /* ignore tty signals */
	signal(SIGTTOU, SIG_IGN);
	signal(SIGTTIN, SIG_IGN);
	signal(SIGHUP, signal_handler); /* catch hangup signal */
	signal(SIGTERM, signal_handler); /* catch kill signal */	
	log_message(LOG_FILE, "exampled started ...");
}

int main()
{
	daemonize();
	while(1)
		sleep(1); /*run*/
	return 0;
}