3-13syslog.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <syslog.h>

int main(int argc, const char *argv[])
{
	pid_t pid, sid;
	int i, fd;
	char *buf = "This is a Daemon\n";

	pid = fork();
	if(pid < 0){
		printf("fork error\n");
		return -1;
	}
	else if(pid > 0){
		exit(0);
	}
	else{
		openlog("daemon_syslog", LOG_PID, LOG_DAEMON);
		if((sid = setsid()) < 0){
			syslog(LOG_ERR, "%s\n", "setsid");
			exit(1);
		}
		if((sid = chdir("/")) < 0){
			syslog(LOG_ERR, "%s\n", "chdir");
			exit(1);
		}
		umask(0);
		for(i = 0; i < getdtablesize(); i++){
			close(i);
		}

		if((fd = open("/tmp/daemon.log", 
						O_CREAT|O_WRONLY|O_TRUNC, 0600)) < 0){
			syslog(LOG_ERR, "open");
			exit(1);
		}		

		syslog(LOG_INFO, "%s\n", "open daemon.log");

		while(1){
			write(fd, buf, strlen(buf));
			sleep(5);
		}
		close(fd);
		closelog();
	}
	return 0;
}