Issue #3063137 by heddn, tatarbj: Backport ReadOnlyFilesystem

ReadinessCheckers/ReadOnlyFilesystem.php

+<?php
+
+/**
+ * Read only filesystem checker.
+ */
+class ReadOnlyFilesystem implements ReadinessCheckerInterface {
+
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function run() {
+    return static::readOnlyCheck();
+  }
+
+  /**
+   * Check if the filesystem is read only.
+   *
+   * @return array
+   *   An array of translatable strings if any checks fail.
+   */
+  protected  static function readOnlyCheck() {
+    $messages = [];
+
+    // If we can copy and delete a file, then we don't have a read only
+    // file system.
+    $file_path = DRUPAL_ROOT;
+    $file = 'modules/node/node.api.php';
+    if (file_unmanaged_copy("$file_path/$file", "$file_path/$file.automatic_updates", FILE_EXISTS_REPLACE)) {
+      // Delete it after copying.
+      file_unmanaged_delete("$file_path/$file.automatic_updates");
+    }
+    else {
+      $error = t('Filesystem at "@path" is read only. Updates to Drupal core cannot be applied against a read only file system.', ['@path' => DRUPAL_ROOT]);
+      watchdog('automatic_updates', $error, [], WATCHDOG_ERROR);
+      $messages[] = $error;
+    }
+    return $messages;
+  }
+
+}

ReadinessCheckers/ReadinessCheckerManager.php

@@ -26,6 +26,7 @@ class ReadinessCheckerManager {
     static::$checkers['warning'][0][] = 'ModifiedFiles';
     static::$checkers['warning'][0][] = 'PhpSapi';
     static::$checkers['error'][0][] = 'PhpSapi';
+    static::$checkers['error'][0][] = 'ReadOnlyFilesystem';
 
     return static::$checkers;
   }

automatic_updates.info

@@ -12,3 +12,4 @@ files[] = ReadinessCheckers/ReadinessCheckerInterface.php
 files[] = ReadinessCheckers/FileOwnership.php
 files[] = ReadinessCheckers/ModifiedFiles.php
 files[] = ReadinessCheckers/PhpSapi.php
+files[] = ReadinessCheckers/ReadOnlyFilesystem.php