diff --git a/include/functions.php b/include/functions.php
index 2d6716b8160768f6b296caf760638d556a6e3736..8ede14a0bfa7a188b036d8ac704aff70dd7c22a9 100644
--- a/include/functions.php
+++ b/include/functions.php
@@ -139,6 +139,8 @@
 	 * @return void
 	 */
 	function _debug($msg, $show = true) {
+		if (defined('SUPPRESS_DEBUGGING'))
+			return false;
 
 		$ts = strftime("%H:%M:%S", time());
 		if (function_exists('posix_getpid')) {
@@ -153,7 +155,29 @@
 			$fp = fopen(LOGFILE, 'a+');
 
 			if ($fp) {
+				$locked = false;
+
+				if (function_exists("flock")) {
+					$tries = 0;
+
+					// try to lock logfile for writing
+					while ($tries < 5 && !$locked = flock($fp, LOCK_EX | LOCK_NB)) {
+						sleep(1);
+						++$tries;
+					}
+
+					if (!$locked) {
+						fclose($fp);
+						return;
+					}
+				}
+
 				fputs($fp, "[$ts] $msg\n");
+
+				if (function_exists("flock")) {
+					flock($fp, LOCK_UN);
+				}
+
 				fclose($fp);
 			}
 		}
diff --git a/include/rssfuncs.php b/include/rssfuncs.php
index 2bc30b5ce0f2fdd6ec70f82d6a9f6c647e0adb80..7f6417759e1a8b7f310414f186d893618275c85e 100644
--- a/include/rssfuncs.php
+++ b/include/rssfuncs.php
@@ -194,6 +194,8 @@
 
 		$debug_enabled = defined('DAEMON_EXTENDED_DEBUG') || $_REQUEST['xdebug'];
 
+		if (!$debug_enabled) define('SUPPRESS_DEBUGGING', true);
+
 		_debug("start", $debug_enabled);
 
 		$result = db_query("SELECT id,update_interval,auth_login,
diff --git a/update_daemon2.php b/update_daemon2.php
index 9d948a64d3c5cdea2e19cea5e1fcfa8d9f04c5ae..e5bc55ee089474dd5696119b2f211c55b7275b5f 100755
--- a/update_daemon2.php
+++ b/update_daemon2.php
@@ -218,10 +218,11 @@
 					register_shutdown_function('task_shutdown');
 
 					$quiet = (isset($options["quiet"])) ? "--quiet" : "";
+					$log = function_exists("flock") && isset($options['log']) ? '--log '.$options['log'] : '';
 
 					$my_pid = posix_getpid();
 
-					passthru(PHP_EXECUTABLE . " update.php --daemon-loop $quiet --task $j --pidlock $my_pid");
+					passthru(PHP_EXECUTABLE . " update.php --daemon-loop $quiet $log --task $j --pidlock $my_pid");
 
 					sleep(1);