diff --git a/core/includes/common.inc b/core/includes/common.inc
index 323a666..9bb16f7 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -1244,7 +1244,7 @@ function archiver_get_extensions() {
  */
 function archiver_get_archiver($file) {
   // Archivers can only work on local paths
-  $filepath = drupal_realpath($file);
+  $filepath = \Drupal::service('file_system')->realpath($file);
   if (!is_file($filepath)) {
     throw new Exception(t('Archivers can only operate on local files: %file not supported', ['%file' => $file]));
   }
diff --git a/core/includes/file.inc b/core/includes/file.inc
index c78ee5b..76f5773 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -452,8 +452,9 @@ function file_unmanaged_copy($source, $destination = NULL, $replace = FILE_EXIST
   }
   // Attempt to resolve the URIs. This is necessary in certain configurations
   // (see above).
-  $real_source = drupal_realpath($source) ?: $source;
-  $real_destination = drupal_realpath($destination) ?: $destination;
+  $file_system = \Drupal::service('file_system');
+  $real_source = $file_system->realpath($source) ?: $source;
+  $real_destination = $file_system->realpath($destination) ?: $destination;
   // Perform the copy operation.
   if (!@copy($real_source, $real_destination)) {
     \Drupal::logger('file')->error('The specified file %file could not be copied to %destination.', ['%file' => $source, '%destination' => $destination]);
@@ -497,12 +498,13 @@ function file_unmanaged_copy($source, $destination = NULL, $replace = FILE_EXIST
 function file_unmanaged_prepare($source, &$destination = NULL, $replace = FILE_EXISTS_RENAME) {
   $original_source = $source;
   $logger = \Drupal::logger('file');
+  $file_system = \Drupal::service('file_system');
 
   // Assert that the source file actually exists.
   if (!file_exists($source)) {
     // @todo Replace drupal_set_message() calls with exceptions instead.
     drupal_set_message(t('The specified file %file could not be moved/copied because no file by that name exists. Please check that you supplied the correct filename.', ['%file' => $original_source]), 'error');
-    if (($realpath = drupal_realpath($original_source)) !== FALSE) {
+    if (($realpath = $file_system->realpath($original_source)) !== FALSE) {
       $logger->notice('File %file (%realpath) could not be moved/copied because it does not exist.', ['%file' => $original_source, '%realpath' => $realpath]);
     }
     else {
@@ -542,8 +544,8 @@ function file_unmanaged_prepare($source, &$destination = NULL, $replace = FILE_E
   }
 
   // Assert that the source and destination filenames are not the same.
-  $real_source = drupal_realpath($source);
-  $real_destination = drupal_realpath($destination);
+  $real_source = $file_system->realpath($source);
+  $real_destination = $file_system->realpath($destination);
   if ($source == $destination || ($real_source !== FALSE) && ($real_source == $real_destination)) {
     drupal_set_message(t('The specified file %file was not moved/copied because it would overwrite itself.', ['%file' => $source]), 'error');
     $logger->notice('File %file could not be moved/copied because it would overwrite itself.', ['%file' => $source]);
@@ -643,8 +645,9 @@ function file_unmanaged_move($source, $destination = NULL, $replace = FILE_EXIST
   }
   // Attempt to resolve the URIs. This is necessary in certain configurations
   // (see above) and can also permit fast moves across local schemes.
-  $real_source = drupal_realpath($source) ?: $source;
-  $real_destination = drupal_realpath($destination) ?: $destination;
+  $file_system = \Drupal::service('file_system');
+  $real_source = $file_system->realpath($source) ?: $source;
+  $real_destination = $file_system->realpath($destination) ?: $destination;
   // Perform the move operation.
   if (!@rename($real_source, $real_destination)) {
     // Fall back to slow copy and unlink procedure. This is necessary for
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index cfc0497..7a434c4 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -1375,7 +1375,7 @@ function install_download_translation(&$install_state) {
  */
 function install_retrieve_file($uri, $destination) {
   $parsed_url = parse_url($uri);
-  if (is_dir(drupal_realpath($destination))) {
+  if (is_dir(\Drupal::service('file_system')->realpath($destination))) {
     // Prevent URIs with triple slashes when gluing parts together.
     $path = str_replace('///', '//', "$destination/") . drupal_basename($parsed_url['path']);
   }
diff --git a/core/lib/Drupal/Core/FileTransfer/FileTransfer.php b/core/lib/Drupal/Core/FileTransfer/FileTransfer.php
index 25014f1..79becc8 100644
--- a/core/lib/Drupal/Core/FileTransfer/FileTransfer.php
+++ b/core/lib/Drupal/Core/FileTransfer/FileTransfer.php
@@ -207,7 +207,7 @@ public function __get($name) {
    */
   protected final function checkPath($path) {
     $full_jail = $this->chroot . $this->jail;
-    $full_path = drupal_realpath(substr($this->chroot . $path, 0, strlen($full_jail)));
+    $full_path = \Drupal::service('file_system')->realpath(substr($this->chroot . $path, 0, strlen($full_jail)));
     $full_path = $this->fixRemotePath($full_path, FALSE);
     if ($full_jail !== $full_path) {
       throw new FileTransferException('@directory is outside of the @jail', NULL, ['@directory' => $path, '@jail' => $this->jail]);
diff --git a/core/modules/color/color.module b/core/modules/color/color.module
index 20d099a..25d4874 100644
--- a/core/modules/color/color.module
+++ b/core/modules/color/color.module
@@ -635,7 +635,7 @@ function _color_render_images($theme, &$info, &$paths, $palette) {
   foreach ($info['slices'] as $file => $coord) {
     list($x, $y, $width, $height) = $coord;
     $base = drupal_basename($file);
-    $image = drupal_realpath($paths['target'] . $base);
+    $image = \Drupal::service('file_system')->realpath($paths['target'] . $base);
 
     // Cut out slice.
     if ($file == 'screenshot.png') {
diff --git a/core/modules/color/tests/src/Functional/ColorTest.php b/core/modules/color/tests/src/Functional/ColorTest.php
index 11ff1e7..2cd915f 100644
--- a/core/modules/color/tests/src/Functional/ColorTest.php
+++ b/core/modules/color/tests/src/Functional/ColorTest.php
@@ -141,7 +141,7 @@ public function _testColor($theme, $test_values) {
     $stylesheets = \Drupal::state()->get('drupal_css_cache_files') ?: [];
     $stylesheet_content = '';
     foreach ($stylesheets as $uri) {
-      $stylesheet_content .= join("\n", file(drupal_realpath($uri)));
+      $stylesheet_content .= join("\n", file(\Drupal::service('file_system')->realpath($uri)));
     }
     $this->assertTrue(strpos($stylesheet_content, 'public://') === FALSE, 'Make sure the color paths have been translated to local paths. (' . $theme . ')');
     $config->set('css.preprocess', 0);
diff --git a/core/modules/comment/src/Tests/CommentPreviewTest.php b/core/modules/comment/src/Tests/CommentPreviewTest.php
index 1b07fe6..89cea53 100644
--- a/core/modules/comment/src/Tests/CommentPreviewTest.php
+++ b/core/modules/comment/src/Tests/CommentPreviewTest.php
@@ -55,7 +55,7 @@ public function testCommentPreview() {
 
     // Add a user picture.
     $image = current($this->drupalGetTestFiles('image'));
-    $user_edit['files[user_picture_0]'] = drupal_realpath($image->uri);
+    $user_edit['files[user_picture_0]'] = \Drupal::service('file_system')->realpath($image->uri);
     $this->drupalPostForm('user/' . $this->webUser->id() . '/edit', $user_edit, t('Save'));
 
     // As the web user, fill in the comment form and preview the comment.
diff --git a/core/modules/config/src/Tests/ConfigImportUploadTest.php b/core/modules/config/src/Tests/ConfigImportUploadTest.php
index 5e21295..4214f72 100644
--- a/core/modules/config/src/Tests/ConfigImportUploadTest.php
+++ b/core/modules/config/src/Tests/ConfigImportUploadTest.php
@@ -42,7 +42,7 @@ public function testImport() {
 
     // Attempt to upload a non-tar file.
     $text_file = current($this->drupalGetTestFiles('text'));
-    $edit = ['files[import_tarball]' => drupal_realpath($text_file->uri)];
+    $edit = ['files[import_tarball]' => \Drupal::service('file_system')->realpath($text_file->uri)];
     $this->drupalPostForm('admin/config/development/configuration/full/import', $edit, t('Upload'));
     $this->assertText(t('Could not extract the contents of the tar file'));
 
diff --git a/core/modules/editor/src/Tests/EditorUploadImageScaleTest.php b/core/modules/editor/src/Tests/EditorUploadImageScaleTest.php
index 5ac88c7..100fb4f 100644
--- a/core/modules/editor/src/Tests/EditorUploadImageScaleTest.php
+++ b/core/modules/editor/src/Tests/EditorUploadImageScaleTest.php
@@ -188,7 +188,7 @@ protected function setMaxDimensions($width, $height) {
    */
   protected function uploadImage($uri) {
     $edit = [
-      'files[fid]' => drupal_realpath($uri),
+      'files[fid]' => \Drupal::service('file_system')->realpath($uri),
     ];
     $this->drupalGet('editor/dialog/image/basic_html');
     $this->drupalPostForm('editor/dialog/image/basic_html', $edit, t('Upload'));
diff --git a/core/modules/field/src/Tests/EntityReference/EntityReferenceFileUploadTest.php b/core/modules/field/src/Tests/EntityReference/EntityReferenceFileUploadTest.php
index 1957584..fc21e50 100644
--- a/core/modules/field/src/Tests/EntityReference/EntityReferenceFileUploadTest.php
+++ b/core/modules/field/src/Tests/EntityReference/EntityReferenceFileUploadTest.php
@@ -115,7 +115,7 @@ public function testFileUpload() {
     $this->drupalLogin($user1);
 
     $test_file = current($this->drupalGetTestFiles('text'));
-    $edit['files[file_field_0]'] = drupal_realpath($test_file->uri);
+    $edit['files[file_field_0]'] = \Drupal::service('file_system')->realpath($test_file->uri);
     $this->drupalPostForm('node/add/' . $this->referencingType, $edit, 'Upload');
     $this->assertResponse(200);
     $edit = [
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index a6fc3f6..5201290 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -140,7 +140,7 @@ function file_load($fid, $reset = FALSE) {
  */
 function file_copy(FileInterface $source, $destination = NULL, $replace = FILE_EXISTS_RENAME) {
   if (!file_valid_uri($destination)) {
-    if (($realpath = drupal_realpath($source->getFileUri())) !== FALSE) {
+    if (($realpath = \Drupal::service('file_system')->realpath($source->getFileUri())) !== FALSE) {
       \Drupal::logger('file')->notice('File %file (%realpath) could not be copied because the destination %destination is invalid. This is often caused by improper use of file_copy() or a missing stream wrapper.', ['%file' => $source->getFileUri(), '%realpath' => $realpath, '%destination' => $destination]);
     }
     else {
@@ -215,7 +215,7 @@ function file_copy(FileInterface $source, $destination = NULL, $replace = FILE_E
  */
 function file_move(FileInterface $source, $destination = NULL, $replace = FILE_EXISTS_RENAME) {
   if (!file_valid_uri($destination)) {
-    if (($realpath = drupal_realpath($source->getFileUri())) !== FALSE) {
+    if (($realpath = \Drupal::service('file_system')->realpath($source->getFileUri())) !== FALSE) {
       \Drupal::logger('file')->notice('File %file (%realpath) could not be moved because the destination %destination is invalid. This may be caused by improper use of file_move() or a missing stream wrapper.', ['%file' => $source->getFileUri(), '%realpath' => $realpath, '%destination' => $destination]);
     }
     else {
diff --git a/core/modules/file/src/Tests/FileFieldDisplayTest.php b/core/modules/file/src/Tests/FileFieldDisplayTest.php
index 1b7e534..cce0821 100644
--- a/core/modules/file/src/Tests/FileFieldDisplayTest.php
+++ b/core/modules/file/src/Tests/FileFieldDisplayTest.php
@@ -96,7 +96,7 @@ public function testNodeDisplay() {
     // Test that fields appear as expected after during the preview.
     // Add a second file.
     $name = 'files[' . $field_name . '_1][]';
-    $edit[$name] = drupal_realpath($test_file->getFileUri());
+    $edit[$name] = \Drupal::service('file_system')->realpath($test_file->getFileUri());
 
     // Uncheck the display checkboxes and go to the preview.
     $edit[$field_name . '[0][display]'] = FALSE;
@@ -165,7 +165,7 @@ public function testDescToggle() {
     $title = $this->randomString();
     $edit = [
       'title[0][value]' => $title,
-      'files[field_' . $field_name . '_0]' => drupal_realpath($file->uri),
+      'files[field_' . $field_name . '_0]' => \Drupal::service('file_system')->realpath($file->uri),
     ];
     $this->drupalPostForm('node/add/' . $type_name, $edit, t('Save and publish'));
     $node = $this->drupalGetNodeByTitle($title);
diff --git a/core/modules/file/src/Tests/FileFieldTestBase.php b/core/modules/file/src/Tests/FileFieldTestBase.php
index 73cc96a..99e2c58 100644
--- a/core/modules/file/src/Tests/FileFieldTestBase.php
+++ b/core/modules/file/src/Tests/FileFieldTestBase.php
@@ -251,7 +251,7 @@ public function removeNodeFile($nid, $new_revision = TRUE) {
    */
   public function replaceNodeFile($file, $field_name, $nid, $new_revision = TRUE) {
     $edit = [
-      'files[' . $field_name . '_0]' => drupal_realpath($file->getFileUri()),
+      'files[' . $field_name . '_0]' => \Drupal::service('file_system')->realpath($file->getFileUri()),
       'revision' => (string) (int) $new_revision,
     ];
 
diff --git a/core/modules/file/src/Tests/FileFieldWidgetTest.php b/core/modules/file/src/Tests/FileFieldWidgetTest.php
index ddfd8f4..a867d65 100644
--- a/core/modules/file/src/Tests/FileFieldWidgetTest.php
+++ b/core/modules/file/src/Tests/FileFieldWidgetTest.php
@@ -160,7 +160,7 @@ public function testMultiValuedWidget() {
       $this->drupalGet("node/add/$type_name");
       foreach ([$field_name2, $field_name] as $each_field_name) {
         for ($delta = 0; $delta < 3; $delta++) {
-          $edit = ['files[' . $each_field_name . '_' . $delta . '][]' => drupal_realpath($test_file->getFileUri())];
+          $edit = ['files[' . $each_field_name . '_' . $delta . '][]' => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
           // If the Upload button doesn't exist, drupalPostForm() will automatically
           // fail with an assertion message.
           $this->drupalPostForm(NULL, $edit, t('Upload'));
@@ -374,7 +374,7 @@ public function testPrivateFileComment() {
     // Add a comment with a file.
     $text_file = $this->getTestFile('text');
     $edit = [
-      'files[field_' . $name . '_' . 0 . ']' => drupal_realpath($text_file->getFileUri()),
+      'files[field_' . $name . '_' . 0 . ']' => \Drupal::service('file_system')->realpath($text_file->getFileUri()),
       'comment_body[0][value]' => $comment_body = $this->randomMachineName(),
     ];
     $this->drupalPostForm('node/' . $node->id(), $edit, t('Save'));
@@ -429,7 +429,7 @@ public function testWidgetValidation() {
       $name = 'files[' . $field_name . '_0]';
 
       // Upload file with incorrect extension, check for validation error.
-      $edit[$name] = drupal_realpath($test_file_image->getFileUri());
+      $edit[$name] = \Drupal::service('file_system')->realpath($test_file_image->getFileUri());
       switch ($type) {
         case 'nojs':
           $this->drupalPostForm(NULL, $edit, t('Upload'));
@@ -443,7 +443,7 @@ public function testWidgetValidation() {
       $this->assertRaw($error_message, t('Validation error when file with wrong extension uploaded (JSMode=%type).', ['%type' => $type]));
 
       // Upload file with correct extension, check that error message is removed.
-      $edit[$name] = drupal_realpath($test_file_text->getFileUri());
+      $edit[$name] = \Drupal::service('file_system')->realpath($test_file_text->getFileUri());
       switch ($type) {
         case 'nojs':
           $this->drupalPostForm(NULL, $edit, t('Upload'));
diff --git a/core/modules/file/src/Tests/FileListingTest.php b/core/modules/file/src/Tests/FileListingTest.php
index e348949..12c7ce2 100644
--- a/core/modules/file/src/Tests/FileListingTest.php
+++ b/core/modules/file/src/Tests/FileListingTest.php
@@ -91,7 +91,7 @@ public function testFileListingPages() {
       $file = $this->getTestFile('image');
 
       $edit = [
-        'files[file_0]' => drupal_realpath($file->getFileUri()),
+        'files[file_0]' => \Drupal::service('file_system')->realpath($file->getFileUri()),
       ];
       $this->drupalPostForm(NULL, $edit, t('Save'));
       $node = Node::load($node->id());
diff --git a/core/modules/file/src/Tests/FileManagedFileElementTest.php b/core/modules/file/src/Tests/FileManagedFileElementTest.php
index 8abff25..897cc37 100644
--- a/core/modules/file/src/Tests/FileManagedFileElementTest.php
+++ b/core/modules/file/src/Tests/FileManagedFileElementTest.php
@@ -36,7 +36,7 @@ public function testManagedFile() {
           // was not saved.
           $last_fid_prior = $this->getLastFileId();
           $edit = [
-            $file_field_name => drupal_realpath($test_file->getFileUri()),
+            $file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri()),
             'form_token' => 'invalid token',
           ];
           $this->drupalPostForm($path, $edit, t('Save'));
@@ -46,7 +46,7 @@ public function testManagedFile() {
 
           // Submit a new file, without using the Upload button.
           $last_fid_prior = $this->getLastFileId();
-          $edit = [$file_field_name => drupal_realpath($test_file->getFileUri())];
+          $edit = [$file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
           $this->drupalPostForm($path, $edit, t('Save'));
           $last_fid = $this->getLastFileId();
           $this->assertTrue($last_fid > $last_fid_prior, 'New file got saved.');
@@ -61,7 +61,7 @@ public function testManagedFile() {
             // Upload, then Submit.
             $last_fid_prior = $this->getLastFileId();
             $this->drupalGet($path);
-            $edit = [$file_field_name => drupal_realpath($test_file->getFileUri())];
+            $edit = [$file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
             if ($ajax) {
               $this->drupalPostAjaxForm(NULL, $edit, $input_base_name . '_upload_button');
             }
@@ -92,7 +92,7 @@ public function testManagedFile() {
 
             // Upload, then Remove, then Submit.
             $this->drupalGet($path);
-            $edit = [$file_field_name => drupal_realpath($test_file->getFileUri())];
+            $edit = [$file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
             if ($ajax) {
               $this->drupalPostAjaxForm(NULL, $edit, $input_base_name . '_upload_button');
             }
@@ -120,7 +120,7 @@ public function testManagedFile() {
 
     // The multiple file upload has additional conditions that need checking.
     $path = 'file/test/1/1/1';
-    $edit = ['files[nested_file][]' => drupal_realpath($test_file->getFileUri())];
+    $edit = ['files[nested_file][]' => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
     $fid_list = [];
 
     $this->drupalGet($path);
@@ -158,7 +158,7 @@ public function testManagedFileRemoved() {
     $test_file = $this->getTestFile('text');
     $file_field_name = 'files[nested_file][]';
 
-    $edit = [$file_field_name => drupal_realpath($test_file->getFileUri())];
+    $edit = [$file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
     $this->drupalPostForm(NULL, $edit, t('Upload'));
 
     $fid = $this->getLastFileId();
@@ -179,7 +179,7 @@ public function testFileRemovedFromDisk() {
     $test_file = $this->getTestFile('text');
     $file_field_name = 'files[nested_file][]';
 
-    $edit = [$file_field_name => drupal_realpath($test_file->getFileUri())];
+    $edit = [$file_field_name => \Drupal::service('file_system')->realpath($test_file->getFileUri())];
     $this->drupalPostForm(NULL, $edit, t('Upload'));
     $this->drupalPostForm(NULL, [], t('Save'));
 
diff --git a/core/modules/file/src/Tests/FileOnTranslatedEntityTest.php b/core/modules/file/src/Tests/FileOnTranslatedEntityTest.php
index 5f1e707..6875fe0 100644
--- a/core/modules/file/src/Tests/FileOnTranslatedEntityTest.php
+++ b/core/modules/file/src/Tests/FileOnTranslatedEntityTest.php
@@ -86,7 +86,7 @@ public function testSyncedFiles() {
     // Edit the node to upload a file.
     $edit = [];
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('text')[0]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('text')[0]->uri);
     $this->drupalPostForm('node/' . $default_language_node->id() . '/edit', $edit, t('Save'));
     $first_fid = $this->getLastFileId();
 
@@ -97,7 +97,7 @@ public function testSyncedFiles() {
     $edit = [];
     $edit['title[0][value]'] = 'Bill Murray';
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('text')[1]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('text')[1]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     // This inspects the HTML after the post of the translation, the file
     // should be displayed on the original node.
@@ -123,7 +123,7 @@ public function testSyncedFiles() {
     $edit = [];
     $edit['title[0][value]'] = 'Scarlett Johansson';
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('text')[2]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('text')[2]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     $third_fid = $this->getLastFileId();
 
@@ -151,7 +151,7 @@ public function testSyncedFiles() {
     $edit = [];
     $edit['title[0][value]'] = 'David Bowie';
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('text')[3]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('text')[3]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     $replaced_second_fid = $this->getLastFileId();
 
diff --git a/core/modules/file/src/Tests/PrivateFileOnTranslatedEntityTest.php b/core/modules/file/src/Tests/PrivateFileOnTranslatedEntityTest.php
index da5abb5..2712ce0 100644
--- a/core/modules/file/src/Tests/PrivateFileOnTranslatedEntityTest.php
+++ b/core/modules/file/src/Tests/PrivateFileOnTranslatedEntityTest.php
@@ -80,7 +80,7 @@ public function testPrivateLanguageFile() {
     // Edit the node to upload a file.
     $edit = [];
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('text')[0]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('text')[0]->uri);
     $this->drupalPostForm('node/' . $default_language_node->id() . '/edit', $edit, t('Save'));
     $last_fid_prior = $this->getLastFileId();
 
@@ -105,7 +105,7 @@ public function testPrivateLanguageFile() {
     $edit = [];
     $edit['title[0][value]'] = $this->randomMachineName();
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('text')[1]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('text')[1]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     $last_fid = $this->getLastFileId();
 
diff --git a/core/modules/file/src/Tests/SaveUploadTest.php b/core/modules/file/src/Tests/SaveUploadTest.php
index a9f69c2..a6e6f9a 100644
--- a/core/modules/file/src/Tests/SaveUploadTest.php
+++ b/core/modules/file/src/Tests/SaveUploadTest.php
@@ -60,7 +60,7 @@ protected function setUp() {
     // Upload with replace to guarantee there's something there.
     $edit = [
       'file_test_replace' => FILE_EXISTS_REPLACE,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri()),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri()),
     ];
     $this->drupalPostForm('file-test/upload', $edit, t('Submit'));
     $this->assertResponse(200, 'Received a 200 response for posted test file.');
@@ -88,7 +88,7 @@ public function testNormal() {
 
     // Upload a second file.
     $image2 = current($this->drupalGetTestFiles('image'));
-    $edit = ['files[file_test_upload]' => drupal_realpath($image2->uri)];
+    $edit = ['files[file_test_upload]' => \Drupal::service('file_system')->realpath($image2->uri)];
     $this->drupalPostForm('file-test/upload', $edit, t('Submit'));
     $this->assertResponse(200, 'Received a 200 response for posted test file.');
     $this->assertRaw(t('You WIN!'));
@@ -109,7 +109,7 @@ public function testNormal() {
 
     // Upload a third file to a subdirectory.
     $image3 = current($this->drupalGetTestFiles('image'));
-    $image3_realpath = drupal_realpath($image3->uri);
+    $image3_realpath = \Drupal::service('file_system')->realpath($image3->uri);
     $dir = $this->randomMachineName();
     $edit = [
       'files[file_test_upload]' => $image3_realpath,
@@ -132,7 +132,7 @@ public function testHandleExtension() {
     $extensions = 'foo';
     $edit = [
       'file_test_replace' => FILE_EXISTS_REPLACE,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri()),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri()),
       'extensions' => $extensions,
     ];
 
@@ -152,7 +152,7 @@ public function testHandleExtension() {
     // Now tell file_save_upload() to allow the extension of our test image.
     $edit = [
       'file_test_replace' => FILE_EXISTS_REPLACE,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri()),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri()),
       'extensions' => $extensions,
     ];
 
@@ -170,7 +170,7 @@ public function testHandleExtension() {
     // Now tell file_save_upload() to allow any extension.
     $edit = [
       'file_test_replace' => FILE_EXISTS_REPLACE,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri()),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri()),
       'allow_all_extensions' => TRUE,
     ];
     $this->drupalPostForm('file-test/upload', $edit, t('Submit'));
@@ -191,7 +191,7 @@ public function testHandleDangerousFile() {
     // safety. Also check to make sure its MIME type was changed.
     $edit = [
       'file_test_replace' => FILE_EXISTS_REPLACE,
-      'files[file_test_upload]' => drupal_realpath($this->phpfile->uri),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->phpfile->uri),
       'is_image_file' => FALSE,
       'extensions' => 'php',
     ];
@@ -238,7 +238,7 @@ public function testHandleFileMunge() {
 
     $extensions = $this->imageExtension;
     $edit = [
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri()),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri()),
       'extensions' => $extensions,
     ];
 
@@ -260,7 +260,7 @@ public function testHandleFileMunge() {
     file_test_reset();
 
     $edit = [
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri()),
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri()),
       'allow_all_extensions' => TRUE,
     ];
 
@@ -280,7 +280,7 @@ public function testHandleFileMunge() {
   public function testExistingRename() {
     $edit = [
       'file_test_replace' => FILE_EXISTS_RENAME,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri())
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri())
     ];
     $this->drupalPostForm('file-test/upload', $edit, t('Submit'));
     $this->assertResponse(200, 'Received a 200 response for posted test file.');
@@ -296,7 +296,7 @@ public function testExistingRename() {
   public function testExistingReplace() {
     $edit = [
       'file_test_replace' => FILE_EXISTS_REPLACE,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri())
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri())
     ];
     $this->drupalPostForm('file-test/upload', $edit, t('Submit'));
     $this->assertResponse(200, 'Received a 200 response for posted test file.');
@@ -312,7 +312,7 @@ public function testExistingReplace() {
   public function testExistingError() {
     $edit = [
       'file_test_replace' => FILE_EXISTS_ERROR,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri())
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri())
     ];
     $this->drupalPostForm('file-test/upload', $edit, t('Submit'));
     $this->assertResponse(200, 'Received a 200 response for posted test file.');
@@ -341,7 +341,7 @@ public function testDrupalMovingUploadedFileError() {
 
     $edit = [
       'file_subdir' => $test_directory,
-      'files[file_test_upload]' => drupal_realpath($this->image->getFileUri())
+      'files[file_test_upload]' => \Drupal::service('file_system')->realpath($this->image->getFileUri())
     ];
 
     \Drupal::state()->set('file_test.disable_error_collection', TRUE);
diff --git a/core/modules/image/src/Plugin/Field/FieldType/ImageItem.php b/core/modules/image/src/Plugin/Field/FieldType/ImageItem.php
index 7b8b275..4acb6f6 100644
--- a/core/modules/image/src/Plugin/Field/FieldType/ImageItem.php
+++ b/core/modules/image/src/Plugin/Field/FieldType/ImageItem.php
@@ -339,7 +339,7 @@ public static function generateSampleValue(FieldDefinitionInterface $field_defin
       $tmp_file = drupal_tempnam('temporary://', 'generateImage_');
       $destination = $tmp_file . '.' . $extension;
       file_unmanaged_move($tmp_file, $destination, FILE_CREATE_DIRECTORY);
-      if ($path = $random->image(drupal_realpath($destination), $min_resolution, $max_resolution)) {
+      if ($path = $random->image(\Drupal::service('file_system')->realpath($destination), $min_resolution, $max_resolution)) {
         $image = File::create();
         $image->setFileUri($path);
         $image->setOwnerId(\Drupal::currentUser()->id());
diff --git a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php b/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
index d04a1c4..22d0e01 100644
--- a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
+++ b/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
@@ -302,7 +302,7 @@ public function testDefaultImages() {
     );
 
     $non_image = $this->drupalGetTestFiles('text');
-    $this->drupalPostForm(NULL, ['files[settings_default_image_uuid]' => drupal_realpath($non_image[0]->uri)], t("Upload"));
+    $this->drupalPostForm(NULL, ['files[settings_default_image_uuid]' => \Drupal::service('file_system')->realpath($non_image[0]->uri)], t("Upload"));
     $this->assertText('The specified file text-0.txt could not be uploaded.');
     $this->assertText('Only files with the following extensions are allowed: png gif jpg jpeg.');
 
diff --git a/core/modules/image/src/Tests/ImageFieldDisplayTest.php b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
index 9c105c1..2e1edf4 100644
--- a/core/modules/image/src/Tests/ImageFieldDisplayTest.php
+++ b/core/modules/image/src/Tests/ImageFieldDisplayTest.php
@@ -312,7 +312,7 @@ public function testImageFieldSettings() {
     // @see FileWidget::formMultipleElements().
     $this->drupalPostForm('admin/structure/types/manage/article/fields/node.article.' . $field_name . '/storage', ['cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED], t('Save field settings'));
     $edit = [
-      'files[' . $field_name . '_1][]' => drupal_realpath($test_image->uri),
+      'files[' . $field_name . '_1][]' => \Drupal::service('file_system')->realpath($test_image->uri),
     ];
     $this->drupalPostForm('node/' . $node->id() . '/edit', $edit, t('Save and keep published'));
     // Add the required alt text.
@@ -322,7 +322,7 @@ public function testImageFieldSettings() {
     // Assert ImageWidget::process() calls FieldWidget::process().
     $this->drupalGet('node/' . $node->id() . '/edit');
     $edit = [
-      'files[' . $field_name . '_2][]' => drupal_realpath($test_image->uri),
+      'files[' . $field_name . '_2][]' => \Drupal::service('file_system')->realpath($test_image->uri),
     ];
     $this->drupalPostAjaxForm(NULL, $edit, $field_name . '_2_upload_button');
     $this->assertNoRaw('<input multiple type="file" id="edit-' . strtr($field_name, '_', '-') . '-2-upload" name="files[' . $field_name . '_2][]" size="22" class="js-form-file form-file">');
@@ -357,7 +357,7 @@ public function testImageFieldDefaultImage() {
     $title = $this->randomString(1024);
     $edit = [
       // Get the path of the 'image-test.png' file.
-      'files[settings_default_image_uuid]' => drupal_realpath($images[0]->uri),
+      'files[settings_default_image_uuid]' => \Drupal::service('file_system')->realpath($images[0]->uri),
       'settings[default_image][alt]' => $alt,
       'settings[default_image][title]' => $title,
     ];
@@ -426,7 +426,7 @@ public function testImageFieldDefaultImage() {
     // Add a default image to the new field.
     $edit = [
       // Get the path of the 'image-test.gif' file.
-      'files[settings_default_image_uuid]' => drupal_realpath($images[2]->uri),
+      'files[settings_default_image_uuid]' => \Drupal::service('file_system')->realpath($images[2]->uri),
       'settings[default_image][alt]' => $alt,
       'settings[default_image][title]' => $title,
     ];
diff --git a/core/modules/image/src/Tests/ImageFieldTestBase.php b/core/modules/image/src/Tests/ImageFieldTestBase.php
index eec7f7b..9cddf35 100644
--- a/core/modules/image/src/Tests/ImageFieldTestBase.php
+++ b/core/modules/image/src/Tests/ImageFieldTestBase.php
@@ -69,7 +69,7 @@ public function previewNodeImage($image, $field_name, $type) {
     $edit = [
       'title[0][value]' => $this->randomMachineName(),
     ];
-    $edit['files[' . $field_name . '_0]'] = drupal_realpath($image->uri);
+    $edit['files[' . $field_name . '_0]'] = \Drupal::service('file_system')->realpath($image->uri);
     $this->drupalPostForm('node/add/' . $type, $edit, t('Preview'));
   }
 
@@ -89,7 +89,7 @@ public function uploadNodeImage($image, $field_name, $type, $alt = '') {
     $edit = [
       'title[0][value]' => $this->randomMachineName(),
     ];
-    $edit['files[' . $field_name . '_0]'] = drupal_realpath($image->uri);
+    $edit['files[' . $field_name . '_0]'] = \Drupal::service('file_system')->realpath($image->uri);
     $this->drupalPostForm('node/add/' . $type, $edit, t('Save and publish'));
     if ($alt) {
       // Add alt text.
diff --git a/core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php b/core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php
index e1f70d7..23a6592 100644
--- a/core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php
+++ b/core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php
@@ -92,7 +92,7 @@ public function testSyncedImages() {
     // Edit the node to upload a file.
     $edit = [];
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('image')[0]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('image')[0]->uri);
     $this->drupalPostForm('node/' . $default_language_node->id() . '/edit', $edit, t('Save'));
     $edit = [$this->fieldName . '[0][alt]' => 'Lost in translation image', $this->fieldName . '[0][title]' => 'Lost in translation image title'];
     $this->drupalPostForm(NULL, $edit, t('Save'));
@@ -105,7 +105,7 @@ public function testSyncedImages() {
     $edit = [];
     $edit['title[0][value]'] = 'Scarlett Johansson';
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('image')[1]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('image')[1]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     $edit = [$this->fieldName . '[0][alt]' => 'Scarlett Johansson image', $this->fieldName . '[0][title]' => 'Scarlett Johansson image title'];
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
@@ -137,7 +137,7 @@ public function testSyncedImages() {
     $edit = [];
     $edit['title[0][value]'] = 'Akiko Takeshita';
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('image')[2]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('image')[2]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     $edit = [$this->fieldName . '[0][alt]' => 'Akiko Takeshita image', $this->fieldName . '[0][title]' => 'Akiko Takeshita image title'];
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
@@ -172,7 +172,7 @@ public function testSyncedImages() {
     $edit = [];
     $edit['title[0][value]'] = 'Giovanni Ribisi';
     $name = 'files[' . $this->fieldName . '_0]';
-    $edit[$name] = drupal_realpath($this->drupalGetTestFiles('image')[3]->uri);
+    $edit[$name] = \Drupal::service('file_system')->realpath($this->drupalGetTestFiles('image')[3]->uri);
     $this->drupalPostForm(NULL, $edit, t('Save (this translation)'));
     $name = $this->fieldName . '[0][alt]';
 
diff --git a/core/modules/locale/locale.bulk.inc b/core/modules/locale/locale.bulk.inc
index 3e256c2..6beb3fe 100644
--- a/core/modules/locale/locale.bulk.inc
+++ b/core/modules/locale/locale.bulk.inc
@@ -200,7 +200,7 @@ function locale_translate_batch_import($file, array $options, &$context) {
     try {
       if (empty($context['sandbox'])) {
         $context['sandbox']['parse_state'] = [
-          'filesize' => filesize(drupal_realpath($file->uri)),
+          'filesize' => filesize(\Drupal::service('file_system')->realpath($file->uri)),
           'chunk_size' => 200,
           'seek' => 0,
         ];
diff --git a/core/modules/locale/locale.translation.inc b/core/modules/locale/locale.translation.inc
index 571f7d2..526a06c 100644
--- a/core/modules/locale/locale.translation.inc
+++ b/core/modules/locale/locale.translation.inc
@@ -377,7 +377,7 @@ function locale_cron_fill_queue() {
 function _locale_translation_file_is_remote($uri) {
   $scheme = file_uri_scheme($uri);
   if ($scheme) {
-    return !drupal_realpath($scheme . '://');
+    return !\Drupal::service('file_system')->realpath($scheme . '://');
   }
   return FALSE;
 }
diff --git a/core/modules/locale/src/Tests/LocaleUpdateBase.php b/core/modules/locale/src/Tests/LocaleUpdateBase.php
index b228a96..7b98a49 100644
--- a/core/modules/locale/src/Tests/LocaleUpdateBase.php
+++ b/core/modules/locale/src/Tests/LocaleUpdateBase.php
@@ -138,7 +138,7 @@ protected function makePoFile($path, $filename, $timestamp = NULL, array $transl
       'status' => FILE_STATUS_PERMANENT,
     ]);
     file_put_contents($file->getFileUri(), $po_header . $text);
-    touch(drupal_realpath($file->getFileUri()), $timestamp);
+    touch(\Drupal::service('file_system')->realpath($file->getFileUri()), $timestamp);
     $file->save();
   }
 
diff --git a/core/modules/locale/src/Tests/LocaleUpdateCronTest.php b/core/modules/locale/src/Tests/LocaleUpdateCronTest.php
index 78a14ec..8e94c80 100644
--- a/core/modules/locale/src/Tests/LocaleUpdateCronTest.php
+++ b/core/modules/locale/src/Tests/LocaleUpdateCronTest.php
@@ -43,7 +43,7 @@ public function testUpdateCron() {
     // Prepare for test: Simulate new translations being available.
     // Change the last updated timestamp of a translation file.
     $contrib_module_two_uri = 'public://local/contrib_module_two-8.x-2.0-beta4.de._po';
-    touch(drupal_realpath($contrib_module_two_uri), REQUEST_TIME);
+    touch(\Drupal::service('file_system')->realpath($contrib_module_two_uri), REQUEST_TIME);
 
     // Prepare for test: Simulate that the file has not been checked for a long
     // time. Set the last_check timestamp to zero.
diff --git a/core/modules/node/src/Tests/PagePreviewTest.php b/core/modules/node/src/Tests/PagePreviewTest.php
index 37b00d3..64bc077 100644
--- a/core/modules/node/src/Tests/PagePreviewTest.php
+++ b/core/modules/node/src/Tests/PagePreviewTest.php
@@ -171,7 +171,7 @@ public function testPagePreview() {
 
     // Upload an image.
     $test_image = current($this->drupalGetTestFiles('image', 39325));
-    $edit['files[field_image_0][]'] = drupal_realpath($test_image->uri);
+    $edit['files[field_image_0][]'] = \Drupal::service('file_system')->realpath($test_image->uri);
     $this->drupalPostForm('node/add/page', $edit, t('Upload'));
 
     // Add an alt tag and preview the node.
diff --git a/core/modules/system/src/Form/ThemeSettingsForm.php b/core/modules/system/src/Form/ThemeSettingsForm.php
index f5cfb09..5de532d 100644
--- a/core/modules/system/src/Form/ThemeSettingsForm.php
+++ b/core/modules/system/src/Form/ThemeSettingsForm.php
@@ -480,7 +480,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
    */
   protected function validatePath($path) {
     // Absolute local file paths are invalid.
-    if (drupal_realpath($path) == $path) {
+    if (\Drupal::service('file_system')->realpath($path) == $path) {
       return FALSE;
     }
     // A path relative to the Drupal root or a fully qualified URI is valid.
diff --git a/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php b/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
index 818c5b5..308a807 100644
--- a/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
+++ b/core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
@@ -224,7 +224,7 @@ public function save($destination) {
         $destination = drupal_tempnam('temporary://', 'gd_');
       }
       // Convert stream wrapper URI to normal path.
-      $destination = drupal_realpath($destination);
+      $destination = \Drupal::service('file_system')->realpath($destination);
     }
 
     $function = 'image' . image_type_to_extension($this->getType(), FALSE);
diff --git a/core/modules/system/src/Tests/Form/StateValuesCleanAdvancedTest.php b/core/modules/system/src/Tests/Form/StateValuesCleanAdvancedTest.php
index 976209e..9f4353e 100644
--- a/core/modules/system/src/Tests/Form/StateValuesCleanAdvancedTest.php
+++ b/core/modules/system/src/Tests/Form/StateValuesCleanAdvancedTest.php
@@ -38,7 +38,7 @@ public function testFormStateValuesCleanAdvanced() {
     $this->assertTrue(is_file($this->image->uri), "The image file we're going to upload exists.");
 
     // "Browse" for the desired file.
-    $edit = ['files[image]' => drupal_realpath($this->image->uri)];
+    $edit = ['files[image]' => \Drupal::service('file_system')->realpath($this->image->uri)];
 
     // Post the form.
     $this->drupalPostForm('form_test/form-state-values-clean-advanced', $edit, t('Submit'));
diff --git a/core/modules/system/src/Tests/System/ThemeTest.php b/core/modules/system/src/Tests/System/ThemeTest.php
index 29d88a3..a02680e 100644
--- a/core/modules/system/src/Tests/System/ThemeTest.php
+++ b/core/modules/system/src/Tests/System/ThemeTest.php
@@ -152,7 +152,7 @@ public function testThemeSettings() {
       // Semi-absolute path to arbitrary non-existing file.
       '/core/misc/whatever.png',
       // Absolute paths to any local file (even if it exists).
-      drupal_realpath($file->uri),
+      \Drupal::service('file_system')->realpath($file->uri),
     ];
     $this->drupalGet('admin/appearance/settings');
     foreach ($unsupported_paths as $path) {
@@ -168,7 +168,7 @@ public function testThemeSettings() {
     $edit = [
       'default_logo' => FALSE,
       'logo_path' => '',
-      'files[logo_upload]' => drupal_realpath($file->uri),
+      'files[logo_upload]' => \Drupal::service('file_system')->realpath($file->uri),
     ];
     $this->drupalPostForm('admin/appearance/settings', $edit, t('Save configuration'));
 
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 614ad9e..ba8321b 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -466,19 +466,20 @@ function system_requirements($phase) {
     // Try to write the .htaccess files first, to prevent false alarms in case
     // (for example) the /tmp directory was wiped.
     file_ensure_htaccess();
+    $file_system = \Drupal::service('file_system');
     $htaccess_files['public://.htaccess'] = [
       'title' => t('Public files directory'),
-      'directory' => drupal_realpath('public://'),
+      'directory' => $file_system->realpath('public://'),
     ];
     if (PrivateStream::basePath()) {
       $htaccess_files['private://.htaccess'] = [
         'title' => t('Private files directory'),
-        'directory' => drupal_realpath('private://'),
+        'directory' => $file_system->realpath('private://'),
       ];
     }
     $htaccess_files['temporary://.htaccess'] = [
       'title' => t('Temporary files directory'),
-      'directory' => drupal_realpath('temporary://'),
+      'directory' => $file_system->realpath('temporary://'),
     ];
     foreach ($htaccess_files as $htaccess_file => $info) {
       // Check for the string which was added to the recommended .htaccess file
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index a1a6b71..49bb5cc 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1410,7 +1410,7 @@ function system_retrieve_file($url, $destination = NULL, $managed = FALSE, $repl
     $path = file_build_uri(drupal_basename($parsed_url['path']));
   }
   else {
-    if (is_dir(drupal_realpath($destination))) {
+    if (is_dir(\Drupal::service('file_system')->realpath($destination))) {
       // Prevent URIs with triple slashes when glueing parts together.
       $path = str_replace('///', '//', "$destination/") . drupal_basename($parsed_url['path']);
     }
diff --git a/core/modules/taxonomy/src/Tests/TaxonomyImageTest.php b/core/modules/taxonomy/src/Tests/TaxonomyImageTest.php
index 7d2ee2b..94a9792 100644
--- a/core/modules/taxonomy/src/Tests/TaxonomyImageTest.php
+++ b/core/modules/taxonomy/src/Tests/TaxonomyImageTest.php
@@ -74,7 +74,7 @@ public function testTaxonomyImageAccess() {
     $files = $this->drupalGetTestFiles('image');
     $image = array_pop($files);
     $edit['name[0][value]'] = $this->randomMachineName();
-    $edit['files[field_test_0]'] = drupal_realpath($image->uri);
+    $edit['files[field_test_0]'] = \Drupal::service('file_system')->realpath($image->uri);
     $this->drupalPostForm('admin/structure/taxonomy/manage/' . $this->vocabulary->id() . '/add', $edit, t('Save'));
     $this->drupalPostForm(NULL, ['field_test[0][alt]' => $this->randomMachineName()], t('Save'));
     $terms = entity_load_multiple_by_properties('taxonomy_term', ['name' => $edit['name[0][value]']]);
diff --git a/core/modules/text/src/Tests/TextFieldTest.php b/core/modules/text/src/Tests/TextFieldTest.php
index d061c00..f3fb43f 100644
--- a/core/modules/text/src/Tests/TextFieldTest.php
+++ b/core/modules/text/src/Tests/TextFieldTest.php
@@ -113,7 +113,7 @@ public function testRequiredLongTextWithFileUpload() {
       ->save();
 
     $test_file = current($this->drupalGetTestFiles('text'));
-    $edit['files[file_field_0]'] = drupal_realpath($test_file->uri);
+    $edit['files[file_field_0]'] = \Drupal::service('file_system')->realpath($test_file->uri);
     $this->drupalPostForm('entity_test/add', $edit, 'Upload');
     $this->assertResponse(200);
     $edit = [
diff --git a/core/modules/update/src/Form/UpdateManagerInstall.php b/core/modules/update/src/Form/UpdateManagerInstall.php
index b141182..9278c2b 100644
--- a/core/modules/update/src/Form/UpdateManagerInstall.php
+++ b/core/modules/update/src/Form/UpdateManagerInstall.php
@@ -212,7 +212,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
       return;
     }
 
-    $project_real_location = drupal_realpath($project_location);
+    $project_real_location = \Drupal::service('file_system')->realpath($project_location);
     $arguments = [
       'project' => $project,
       'updater_name' => get_class($updater),
diff --git a/core/modules/update/src/Form/UpdateReady.php b/core/modules/update/src/Form/UpdateReady.php
index ef9a2f1..1965dfe 100644
--- a/core/modules/update/src/Form/UpdateReady.php
+++ b/core/modules/update/src/Form/UpdateReady.php
@@ -136,7 +136,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
       foreach ($projects as $project => $url) {
         $project_location = $directory . '/' . $project;
         $updater = Updater::factory($project_location, $this->root);
-        $project_real_location = drupal_realpath($project_location);
+        $project_real_location = \Drupal::service('file_system')->realpath($project_location);
         $updates[] = [
           'project' => $project,
           'updater_name' => get_class($updater),
diff --git a/core/modules/update/src/Tests/UpdateDeleteFileIfStaleTest.php b/core/modules/update/src/Tests/UpdateDeleteFileIfStaleTest.php
index 99499d7..7e18dd2 100644
--- a/core/modules/update/src/Tests/UpdateDeleteFileIfStaleTest.php
+++ b/core/modules/update/src/Tests/UpdateDeleteFileIfStaleTest.php
@@ -38,7 +38,7 @@ public function testUpdateDeleteFileIfStale() {
       ->set('temporary_maximum_age', -100000)
       ->save();
 
-    $file_path = drupal_realpath($file_name);
+    $file_path = \Drupal::service('file_system')->realpath($file_name);
     update_delete_file_if_stale($file_path);
 
     $this->assertFalse(is_file($file_path));
diff --git a/core/modules/update/update.manager.inc b/core/modules/update/update.manager.inc
index e796007..8c9e14a 100644
--- a/core/modules/update/update.manager.inc
+++ b/core/modules/update/update.manager.inc
@@ -208,7 +208,7 @@ function update_manager_file_get($url) {
   $remote_schemes = ['http', 'https', 'ftp', 'ftps', 'smb', 'nfs'];
   if (!isset($parsed_url['scheme']) || !in_array($parsed_url['scheme'], $remote_schemes)) {
     // This is a local file, just return the path.
-    return drupal_realpath($url);
+    return \Drupal::service('file_system')->realpath($url);
   }
 
   // Check the cache and download the file if needed.
diff --git a/core/modules/user/src/Tests/UserPasswordResetTest.php b/core/modules/user/src/Tests/UserPasswordResetTest.php
index 528d38b..77a9b2e 100644
--- a/core/modules/user/src/Tests/UserPasswordResetTest.php
+++ b/core/modules/user/src/Tests/UserPasswordResetTest.php
@@ -118,7 +118,7 @@ public function testUserPasswordReset() {
     // invalidate the reset token.
     $image = current($this->drupalGetTestFiles('image'));
     $edit = [
-      'files[user_picture_0]' => drupal_realpath($image->uri),
+      'files[user_picture_0]' => \Drupal::service('file_system')->realpath($image->uri),
     ];
     $this->drupalPostAjaxForm(NULL, $edit, 'user_picture_0_upload_button');
 
diff --git a/core/modules/user/src/Tests/UserPictureTest.php b/core/modules/user/src/Tests/UserPictureTest.php
index 6d546f0..bda7bdb 100644
--- a/core/modules/user/src/Tests/UserPictureTest.php
+++ b/core/modules/user/src/Tests/UserPictureTest.php
@@ -130,7 +130,7 @@ public function testPictureOnNodeComment() {
    * Edits the user picture for the test user.
    */
   public function saveUserPicture($image) {
-    $edit = ['files[user_picture_0]' => drupal_realpath($image->uri)];
+    $edit = ['files[user_picture_0]' => \Drupal::service('file_system')->realpath($image->uri)];
     $this->drupalPostForm('user/' . $this->webUser->id() . '/edit', $edit, t('Save'));
 
     // Load actual user data from database.
diff --git a/core/tests/Drupal/KernelTests/Core/File/DirectoryTest.php b/core/tests/Drupal/KernelTests/Core/File/DirectoryTest.php
index 4e35821..467d926 100644
--- a/core/tests/Drupal/KernelTests/Core/File/DirectoryTest.php
+++ b/core/tests/Drupal/KernelTests/Core/File/DirectoryTest.php
@@ -45,7 +45,7 @@ public function testFileCheckLocalDirectoryHandling() {
     $this->assertDirectoryPermissions($directory, $old_mode);
 
     // Check creating a directory using an absolute path.
-    $absolute_path = drupal_realpath($directory) . DIRECTORY_SEPARATOR . $this->randomMachineName() . DIRECTORY_SEPARATOR . $this->randomMachineName();
+    $absolute_path = \Drupal::service('file_system')->realpath($directory) . DIRECTORY_SEPARATOR . $this->randomMachineName() . DIRECTORY_SEPARATOR . $this->randomMachineName();
     $this->assertTrue(drupal_mkdir($absolute_path, 0775, TRUE), 'No error reported when creating new absolute directories.', 'File');
     $this->assertDirectoryPermissions($absolute_path, 0775);
   }