WIP: Added option to daemonize app and set PID file.

src/daemon.c

@@ -29,11 +29,16 @@
 #include <signal.h>
 #include <getopt.h>
 #include <string.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 
 static int running = 0;
 static int delay = 1;
 static int counter = 0;
 static char *conf_file_name = NULL;
+static char *pid_file_name = NULL;
+static int pid_fd = -1;
 static char *app_name = NULL;
 static FILE *log_stream;
 
@@ -99,16 +104,109 @@ int test_conf_file(char *_conf_file_name)
  * \brief Callback function for handling signals.
  * \param	sig	identifier of signal
  */
-void vs_handle_signal(int sig)
+void handle_signal(int sig)
 {
 	if(sig == SIGINT) {
 		fprintf(log_stream, "Debug: stopping daemon ...\n");
+		/* Unlock and close lockfile */
+		if(pid_fd != -1) {
+			lockf(pid_fd, F_ULOCK, 0);
+			close(pid_fd);
+		}
+		/* Try to delete lockfile */
+		if(pid_file_name != NULL) {
+			unlink(pid_file_name);
+		}
 		running = 0;
 		/* Reset signal handling to default behavior */
 		signal(SIGINT, SIG_DFL);
 	} else if(sig == SIGHUP) {
 		fprintf(log_stream, "Debug: reloading daemon config file ...\n");
 		read_conf_file();
+	} else if(sig == SIGCHLD) {
+		fprintf(log_stream, "Debug: received SIGCHLD signal\n");
+	}
+}
+
+/**
+ * \brief This function will daemonize this app
+ */
+static void daemonize()
+{
+	pid_t pid = 0;
+	int fd;
+
+	/* Fork off the parent process */
+	pid = fork();
+
+	/* An error occurred */
+	if(pid < 0) {
+		exit(EXIT_FAILURE);
+	}
+
+	/* Success: Let the parent terminate */
+	if(pid > 0) {
+		exit(EXIT_SUCCESS);
+	}
+
+	/* On success: The child process becomes session leader */
+	if(setsid() < 0) {
+		exit(EXIT_FAILURE);
+	}
+
+	/* Ignore signal sent from child to parent process */
+	signal(SIGCHLD, SIG_IGN);
+
+	/* Fork off for the second time*/
+	pid = fork();
+
+	/* An error occurred */
+	if(pid < 0) {
+		exit(EXIT_FAILURE);
+	}
+
+	/* Success: Let the parent terminate */
+	if(pid > 0) {
+		exit(EXIT_SUCCESS);
+	}
+
+	/* Set new file permissions */
+	umask(0);
+
+	/* Change the working directory to the root directory */
+	/* or another appropriated directory */
+	chdir("/");
+
+	/* Close all open file descriptors */
+	for(fd = sysconf(_SC_OPEN_MAX); fd > 0; fd--)
+	{
+		close(fd);
+	}
+
+	/* Reopen stdin (fd = 0), stdout (fd = 1), stderr (fd = 2) */
+	stdin = fopen("/dev/null", "r");
+	stdout = fopen("/dev/null", "w+");
+	stderr = fopen("/dev/null", "w+");
+
+	/* Try to write PID of daemon to lockfile */
+	if(pid_file_name != NULL)
+	{
+		char str[256];
+		pid_fd = open(pid_file_name, O_RDWR|O_CREAT, 0640);
+		if(pid_fd < 0)
+		{
+			/* Can't open lockfile */
+			exit(EXIT_FAILURE);
+		}
+		if(lockf(pid_fd, F_TLOCK, 0) < 0)
+		{
+			/* Can't lock file */
+			exit(EXIT_FAILURE);
+		}
+		/* Get current PID */
+		sprintf(str, "%d\n", getpid());
+		/* Write PID to lockfile */
+		write(pid_fd, str, strlen(str));
 	}
 }
 
@@ -119,39 +217,50 @@ void print_help(void)
 {
 	printf("\n Usage: %s [OPTIONS]\n\n", app_name);
 	printf("  Options:\n");
-	printf("   -h --help               Print this help\n");
-	printf("   -c --confile filename   Read configuration from the file\n");
-	printf("   -t --testconf filename  Test configuration file\n");
-	printf("   -l --logfile filename   Write logs to the file\n");
+	printf("   -h --help                 Print this help\n");
+	printf("   -c --conf_file filename   Read configuration from the file\n");
+	printf("   -t --test_conf filename   Test configuration file\n");
+	printf("   -l --log_file  filename   Write logs to the file\n");
+	printf("   -d --daemon               Daemonize this application\n");
+	printf("   -p --pid_file  filename   PID file used by daemonized app\n");
 	printf("\n");
 }
 
 /* Main function */
 int main(int argc, char *argv[])
 {
 	static struct option long_options[] = {
-		{"confile", required_argument, 0, 'c'},
-		{"testconf", required_argument, 0, 't'},
-		{"logfile", required_argument, 0, 'l'},
+		{"conf_file", required_argument, 0, 'c'},
+		{"test_conf", required_argument, 0, 't'},
+		{"log_file", required_argument, 0, 'l'},
 		{"help", no_argument, 0, 'h'},
+		{"daemon", no_argument, 0, 'd'},
+		{"pid_file", required_argument, 0, 'p'},
 		{NULL, 0, 0, 0}
 	};
 	int value, option_index = 0;
 	char *log_file_name = NULL;
+	int start_daemonized = 0;
 
 	app_name = argv[0];
 
 	/* Try to process all command line arguments */
-	while( (value = getopt_long(argc, argv, "c:l:t:h", long_options, &option_index)) != -1) {
+	while( (value = getopt_long(argc, argv, "c:l:t:p:dh", long_options, &option_index)) != -1) {
 		switch(value) {
 			case 'c':
 				conf_file_name = strdup(optarg);
 				break;
-			case 't':
-				return test_conf_file(optarg);
 			case 'l':
 				log_file_name = strdup(optarg);
 				break;
+			case 'p':
+				pid_file_name = strdup(optarg);
+				break;
+			case 't':
+				return test_conf_file(optarg);
+			case 'd':
+				start_daemonized = 1;
+				break;
 			case 'h':
 				print_help();
 				return EXIT_SUCCESS;
@@ -163,14 +272,21 @@ int main(int argc, char *argv[])
 		}
 	}
 
-	/* Daemon will handle two signals */
-	signal(SIGINT, vs_handle_signal);
-	signal(SIGHUP, vs_handle_signal);
+	/* When daemonizing is requested at command line. */
+	if(start_daemonized == 1) {
+		/* It is also possible to use glibc function deamon()
+		 * at this point, but it is useful to customize your daemon. */
+		daemonize();
+	}
 
 	/* Open system log and write message to it */
-	openlog(argv[0], LOG_PID|LOG_CONS, LOG_USER);
+	openlog(argv[0], LOG_PID|LOG_CONS, LOG_DAEMON);
 	syslog(LOG_INFO, "Started %s", app_name);
 
+	/* Daemon will handle two signals */
+	signal(SIGINT, handle_signal);
+	signal(SIGHUP, handle_signal);
+
 	/* Try to open log file to this daemon */
 	if(log_file_name != NULL) {
 		log_stream = fopen(log_file_name, "a+");
@@ -214,6 +330,7 @@ int main(int argc, char *argv[])
 	/* Free allocated memory */
 	if(conf_file_name != NULL) free(conf_file_name);
 	if(log_file_name != NULL) free(log_file_name);
+	if(pid_file_name != NULL) free(pid_file_name);
 
 	return EXIT_SUCCESS;
 }