/*
UNIX Daemon Server Programming Sample Program
Levent Karakas <levent@mis.boun.edu.tr> 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>

#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 */
}

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

/* EOF */