6 uses of FILE_NOT_WRITABLE

drupal_install_fix_file in core/includes/install.inc
Attempts to fix file permissions.
drupal_install_mkdir in core/includes/install.inc
Creates a directory with the specified permissions.
drupal_verify_install_file in core/includes/install.inc
Verifies the state of the specified file.
SiteConfigureForm::buildForm in core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
Form constructor.
SitesDirectoryHardeningTest::testSitesDirectoryHardening in core/modules/system/tests/src/Functional/System/SitesDirectoryHardeningTest.php
Tests the default behavior to restrict directory permissions is enforced.
system_requirements in core/modules/system/system.install
Implements hook_requirements().

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