Add warning message in case node.config.php isn't writable

src/Core/Config/Util/ConfigFileManager.php

@@ -218,6 +218,22 @@ class ConfigFileManager
 		}
 	}
 
+	/**
+	 * Checks, if the node.config.php is writable
+	 *
+	 * @return bool
+	 */
+	public function dataIsWritable(): bool
+	{
+		$filename = $this->configDir . '/' . self::CONFIG_DATA_FILE;
+
+		if (file_exists($filename)) {
+			return is_writable($filename);
+		} else {
+			return is_writable($this->configDir);
+		}
+	}
+
 	/**
 	 * Saves overridden config entries back into the data.config.php
 	 *
@@ -229,6 +245,11 @@ class ConfigFileManager
 	{
 		$filename = $this->configDir . '/' . self::CONFIG_DATA_FILE;
 
+		// fail at a early stage, if we already know that we cannot save the data
+		if (!$this->dataIsWritable()) {
+			throw new ConfigFileException(sprintf('Cannot open file "%s" in mode c+', $filename));
+		}
+
 		if (file_exists($filename)) {
 			$fileExists = true;
 		} else {
@@ -238,13 +259,15 @@ class ConfigFileManager
 		/**
 		 * Creates a read-write stream
 		 *
-		 * @see https://www.php.net/manual/en/function.fopen.php
+		 * @see  https://www.php.net/manual/en/function.fopen.php
 		 * @note Open the file for reading and writing. If the file does not exist, it is created.
 		 * If it exists, it is neither truncated (as opposed to 'w'), nor the call to this function fails
 		 * (as is the case with 'x'). The file pointer is positioned on the beginning of the file.
 		 *
 		 */
-		$configStream = fopen($filename, 'c+');
+		if (($configStream = @fopen($filename, 'c+')) !== false) {
+			throw new ConfigFileException(sprintf('Cannot open file "%s" in mode c+', $filename));
+		}
 
 		try {
 			// We do want an exclusive lock, so we wait until every LOCK_SH (config reading) is unlocked

src/DI.php

@@ -181,6 +181,11 @@ abstract class DI
 		return self::$dice->create(Core\Config\Capability\IManageConfigValues::class);
 	}
 
+	public static function configFileManager(): Core\Config\Util\ConfigFileManager
+	{
+		return self::$dice->create(Core\Config\Util\ConfigFileManager::class);
+	}
+
 	public static function keyValue(): Core\KeyValueStorage\Capabilities\IManageKeyValuePairs
 	{
 		return self::$dice->create(Core\KeyValueStorage\Capabilities\IManageKeyValuePairs::class);

src/Module/Admin/Summary.php

@@ -23,6 +23,7 @@ namespace Friendica\Module\Admin;
 
 use Friendica\App;
 use Friendica\Core\Addon;
+use Friendica\Core\Config\Util\ConfigFileManager;
 use Friendica\Core\Config\ValueObject\Cache;
 use Friendica\Core\Logger;
 use Friendica\Core\Renderer;
@@ -114,6 +115,10 @@ class Summary extends BaseAdmin
 			$warningtext[] = DI::l10n()->t('Friendica\'s configuration now is stored in config/local.config.php, please copy config/local-sample.config.php and move your config from <code>config/local.ini.php</code>. See <a href="%s">the Config help page</a> for help with the transition.', DI::baseUrl()->get() . '/help/Config');
 		}
 
+		if (!DI::configFileManager()->dataIsWritable()) {
+			$warningtext[] = DI::l10n()->t('Friendica\'s configuration store "%s" isn\'t writable. Beware that updates, gui changes and console changes aren\'t working reliable.', ConfigFileManager::CONFIG_DATA_FILE);
+		}
+
 		// Check server vitality
 		if (!self::checkSelfHostMeta()) {
 			$well_known = DI::baseUrl()->get() . Probe::HOST_META;