daemon.c

/*
   UNIX Daemon Server Programming Sample Program
   Levent Karakas <levent at mektup dot at> May 2001

   To compile:	cc -o exampled examped.c
   To run:		./exampled
   To test daemon:	ps -ef|grep exampled (or ps -aux on BSD systems)
   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 <stdio.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>

#define RUNNING_DIR	"/tmp"
#define LOCK_FILE	"exampled.lock"
#define LOG_FILE	"exampled.log"

void log_message(filename,message)
	char *filename;
	char *message;
{
	FILE *logfile;
	logfile=fopen(filename,"a");
	if(!logfile) return;
	fprintf(logfile,"%s\n",message);
	fclose(logfile);
}

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

void daemonize()
{
	int i,lfp;
	char str[10];
	if(getppid()==1) return; /* already a daemon */
	i=fork();
	if (i<0) exit(1); /* fork error */
	if (i>0) exit(0); /* parent exits */
	/* 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); dup(i); dup(i); /* handle standart I/O */
	umask(027); /* set newly created file permissions */
	chdir(RUNNING_DIR); /* change running directory */
	lfp=open(LOCK_FILE,O_RDWR|O_CREAT,0640);
	if (lfp<0) exit(1); /* can not open */
	if (lockf(lfp,F_TLOCK,0)<0) exit(0); /* can not lock */
	/* first instance continues */
	sprintf(str,"%d\n",getpid());
	write(lfp,str,strlen(str)); /* record pid to lockfile */
	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 */
}

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

/* EOF */