diff --git a/.htaccess b/.htaccess
index 4716fa1..c0c52ad 100644
--- a/.htaccess
+++ b/.htaccess
@@ -122,6 +122,9 @@ AddEncoding gzip svgz
   # uncomment the following line:
   # RewriteBase /
 
+  # Pass requests for robots.txt over to index.php, even if robots.txt already exists.
+  RewriteRule ^robots.txt index.php?/$1$2 [last,qsappend]
+
   # Redirect common PHP files to their new locations.
   RewriteCond %{REQUEST_URI} ^(.*)?/(install.php) [OR]
   RewriteCond %{REQUEST_URI} ^(.*)?/(rebuild.php)
diff --git a/core/modules/system/system.api.php b/core/modules/system/system.api.php
index 8534ebf..f25d53e 100644
--- a/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -34,5 +34,29 @@ function hook_system_themes_page_alter(&$theme_groups) {
 }
 
 /**
+ * Appends content to the robots.txt.
+ *
+ * @return array
+ *   An array of strings to append to the end of the robots.txt file.
+ */
+function hook_robotstxt() {
+  return ['Disallow: /tmp/'];
+}
+
+/**
+ * Appends content to the robots.txt.
+ *
+ * @param $robotstxt
+ *   An array of strings printed in the robots.txt.
+ */
+function hook_robotstxt_alter(&$robotstxt) {
+  foreach ($robotstxt as $index => $line) {
+    if ($line == 'Disallow: /tmp/') {
+      $robotstxt[$index] = 'Disallow: /temp/';
+    }
+  }
+}
+
+/**
  * @} End of "addtogroup hooks".
  */
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 2f627be..6b9d8c7 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1454,3 +1454,22 @@ function system_query_entity_reference_alter(AlterableInterface $query) {
   $handler = $query->getMetadata('entity_reference_selection_handler');
   $handler->entityQueryAlter($query);
 }
+
+/**
+ * Implements hook_robotstxt().
+ */
+function system_robotstxt() {
+  // Cache the robots.txt content from the file system.
+  $robotstxt = &drupal_static(__FUNCTION__, array());
+  if (empty($robotstxt)) {
+    if ($cache = \Drupal::cache()->get(__FUNCTION__)) {
+      $robotstxt = $cache->data;
+    }
+    else {
+      $robotstxt = file(realpath('robots.txt'), FILE_IGNORE_NEW_LINES);
+      \Drupal::cache()->set(__FUNCTION__, $robotstxt);
+    }
+  }
+
+  return $robotstxt;
+}
diff --git a/core/modules/system/system.routing.yml b/core/modules/system/system.routing.yml
index ae89fb0..9772e72 100644
--- a/core/modules/system/system.routing.yml
+++ b/core/modules/system/system.routing.yml
@@ -507,3 +507,10 @@ system.csrftoken:
     _controller: '\Drupal\system\Controller\CsrfTokenController::csrfToken'
   requirements:
     _access: 'TRUE'
+
+system.robotstxt:
+  path: '/robots.txt'
+  defaults:
+    _controller: '\Drupal\system\Controller\RobotsTxtController::robotstxt'
+  requirements:
+    _access: 'TRUE'
\ No newline at end of file
diff --git a/sites/default/default.services.yml b/sites/default/default.services.yml
index e1bbbc7..23f6483 100644
--- a/sites/default/default.services.yml
+++ b/sites/default/default.services.yml
@@ -153,22 +153,3 @@ parameters:
     - sftp
     - webcal
     - rtsp
-
-   # Configure Cross-Site HTTP requests (CORS).
-   # Read https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS
-   # for more information about the topic in general.
-   # Note: By default the configuration is disabled.
-  cors.config:
-    enabled: false
-    # Specify allowed headers, like 'x-allowed-header'.
-    allowedHeaders: []
-    # Specify allowed request methods, specify ['*'] to allow all possible ones.
-    allowedMethods: []
-    # Configure requests allowed from specific origins.
-    allowedOrigins: ['*']
-    # Sets the Access-Control-Expose-Headers header.
-    exposedHeaders: false
-    # Sets the Access-Control-Max-Age header.
-    maxAge: false
-    # Sets the Access-Control-Allow-Credentials header.
-    supportsCredentials: false
diff --git a/sites/default/default.settings.php b/sites/default/default.settings.php
index 94a1e04..770a3a7 100644
--- a/sites/default/default.settings.php
+++ b/sites/default/default.settings.php
@@ -144,11 +144,6 @@
  * @code
  *   'prefix' => 'main_',
  * @endcode
- *
- * Per-table prefixes are deprecated as of Drupal 8.2, and will be removed in
- * Drupal 9.0. After that, only a single prefix for all tables will be
- * supported.
- *
  * To provide prefixes for specific tables, set 'prefix' as an array.
  * The array's keys are the table names and the values are the prefixes.
  * The 'default' element is mandatory and holds the prefix for any tables
@@ -330,6 +325,9 @@
  *
  * You can also define an array of host names that can be accessed directly,
  * bypassing the proxy, in $settings['http_client_config']['proxy']['no'].
+ *
+ * If these settings are not configured, the system environment variables
+ * HTTP_PROXY, HTTPS_PROXY, and NO_PROXY on the web server will be used instead.
  */
 # $settings['http_client_config']['proxy']['http'] = 'http://proxy_user:proxy_pass@example.com:8080';
 # $settings['http_client_config']['proxy']['https'] = 'http://proxy_user:proxy_pass@example.com:8080';
@@ -684,15 +682,6 @@
 # $settings['container_base_class'] = '\Drupal\Core\DependencyInjection\Container';
 
 /**
- * Override the default yaml parser class.
- *
- * Provide a fully qualified class name here if you would like to provide an
- * alternate implementation YAML parser. The class must implement the
- * \Drupal\Component\Serialization\SerializationInterface interface.
- */
-# $settings['yaml_parser_class'] = NULL;
-
-/**
  * Trusted host configuration.
  *
  * Drupal core can use the Symfony trusted host mechanism to prevent HTTP Host
@@ -730,21 +719,6 @@
  */
 
 /**
- * The default list of directories that will be ignored by Drupal's file API.
- *
- * By default ignore node_modules and bower_components folders to avoid issues
- * with common frontend tools and recursive scanning of directories looking for
- * extensions.
- *
- * @see file_scan_directory()
- * @see \Drupal\Core\Extension\ExtensionDiscovery::scanDirectory()
- */
-$settings['file_scan_ignore_directories'] = [
-  'node_modules',
-  'bower_components',
-];
-
-/**
  * Load local development override configuration, if available.
  *
  * Use settings.local.php to override variables on secondary (staging,