73 files declare their use of FileSystemInterface

ArchiverManager.php in core/lib/Drupal/Core/Archiver/ArchiverManager.php
AssetDumper.php in core/lib/Drupal/Core/Asset/AssetDumper.php
CKEditor5ImageController.php in core/modules/ckeditor5/src/Controller/CKEditor5ImageController.php
ComponentPluginManager.php in core/lib/Drupal/Core/Theme/ComponentPluginManager.php
ComponentPluginManager.php in core/modules/sdc/src/ComponentPluginManager.php
ConfigController.php in core/modules/config/src/Controller/ConfigController.php
ConfigExportUITest.php in core/modules/config/tests/src/Functional/ConfigExportUITest.php
ConfigImportForm.php in core/modules/config/src/Form/ConfigImportForm.php
CssCollectionOptimizer.php in core/lib/Drupal/Core/Asset/CssCollectionOptimizer.php
CssCollectionOptimizerLazy.php in core/lib/Drupal/Core/Asset/CssCollectionOptimizerLazy.php
CssCollectionOptimizerLazyUnitTest.php in core/tests/Drupal/Tests/Core/Asset/CssCollectionOptimizerLazyUnitTest.php
CssCollectionOptimizerUnitTest.php in core/tests/Drupal/Tests/Core/Asset/CssCollectionOptimizerUnitTest.php
DestructableServiceTest.php in core/tests/Drupal/FunctionalTests/HttpKernel/DestructableServiceTest.php
DirectoryTest.php in core/tests/Drupal/KernelTests/Core/File/DirectoryTest.php
DirectoryWithMetadataDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/DirectoryWithMetadataDiscovery.php
DirectoryWithMetadataDiscovery.php in core/modules/sdc/src/Plugin/Discovery/DirectoryWithMetadataDiscovery.php
DirectoryWithMetadataPluginDiscovery.php in core/lib/Drupal/Core/Plugin/Discovery/DirectoryWithMetadataPluginDiscovery.php
DirectoryWithMetadataPluginDiscovery.php in core/modules/sdc/src/Plugin/Discovery/DirectoryWithMetadataPluginDiscovery.php
Download.php in core/modules/migrate/src/Plugin/migrate/process/Download.php
DownloadTest.php in core/modules/file/tests/src/Functional/DownloadTest.php
EnvironmentCleaner.php in core/lib/Drupal/Core/Test/EnvironmentCleaner.php
ExportForm.php in core/modules/locale/src/Form/ExportForm.php
file.module in core/modules/file/file.module
Defines a "managed_file" Form API field and a "file" field for Field module.
FileCopy.php in core/modules/migrate/src/Plugin/migrate/process/FileCopy.php
FileCopyTest.php in core/modules/migrate/tests/src/Unit/process/FileCopyTest.php
FileExtensionSecureConstraintValidator.php in core/modules/file/src/Plugin/Validation/Constraint/FileExtensionSecureConstraintValidator.php
FileItem.php in core/modules/file/src/Plugin/Field/FieldType/FileItem.php
FilePathTest.php in core/modules/migrate_drupal_ui/tests/src/Functional/d7/FilePathTest.php
FileRepository.php in core/modules/file/src/FileRepository.php
FileStorage.php in core/lib/Drupal/Core/Config/FileStorage.php
FileSystemForm.php in core/modules/system/src/Form/FileSystemForm.php
FileTestForm.php in core/modules/file/tests/file_test/src/Form/FileTestForm.php
FileTestSaveUploadFromForm.php in core/modules/file/tests/file_test/src/Form/FileTestSaveUploadFromForm.php
FileTranslation.php in core/lib/Drupal/Core/StringTranslation/Translator/FileTranslation.php
FileUpload.php in core/modules/jsonapi/src/Controller/FileUpload.php
FileUploadForm.php in core/modules/media_library/src/Form/FileUploadForm.php
FileUploadHandler.php in core/modules/file/src/Upload/FileUploadHandler.php
FileUploadResource.php in core/modules/file/src/Plugin/rest/resource/FileUploadResource.php
FileUrlTest.php in core/modules/file/tests/src/Kernel/FileUrlTest.php
FunctionalTestSetupTrait.php in core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php
GDToolkit.php in core/modules/system/src/Plugin/ImageToolkit/GDToolkit.php
image.install in core/modules/image/image.install
Install, update and uninstall functions for the image module.
image.module in core/modules/image/image.module
Exposes global functionality for creating image styles.
Image.php in core/modules/media/src/Plugin/media/Source/Image.php
ImageItem.php in core/modules/image/src/Plugin/Field/FieldType/ImageItem.php
ImageStyle.php in core/modules/image/src/Entity/ImageStyle.php
ImageStyleDownloadController.php in core/modules/image/src/Controller/ImageStyleDownloadController.php
ImageStylesPathAndUrlTest.php in core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
ImageTest.php in core/tests/Drupal/Tests/Core/Image/ImageTest.php
Importer.php in core/lib/Drupal/Core/DefaultContent/Importer.php
InputStreamFileWriter.php in core/modules/file/src/Upload/InputStreamFileWriter.php
install.core.inc in core/includes/install.core.inc
API functions for installing Drupal.
InstallHelper.php in core/profiles/demo_umami/modules/demo_umami_content/src/InstallHelper.php
JsCollectionOptimizer.php in core/lib/Drupal/Core/Asset/JsCollectionOptimizer.php
JsCollectionOptimizerLazy.php in core/lib/Drupal/Core/Asset/JsCollectionOptimizerLazy.php
LegacyFileSystemTest.php in core/tests/Drupal/KernelTests/Core/File/LegacyFileSystemTest.php
Local.php in core/lib/Drupal/Core/FileTransfer/Local.php
locale.install in core/modules/locale/locale.install
Install, update, and uninstall functions for the Locale module.
locale.module in core/modules/locale/locale.module
Enables the translation of the user interface to languages other than English.
LocaleUpdateBase.php in core/modules/locale/tests/src/Functional/LocaleUpdateBase.php
MailTest.php in core/modules/system/tests/src/Kernel/Mail/MailTest.php
media.install in core/modules/media/media.install
Install, uninstall and update hooks for Media module.
OEmbed.php in core/modules/media/src/Plugin/media/Source/OEmbed.php
SecurityFileUploadEventSubscriber.php in core/modules/system/src/EventSubscriber/SecurityFileUploadEventSubscriber.php
SettingsForm.php in core/modules/navigation/src/Form/SettingsForm.php
SiteSettingsForm.php in core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
StreamWrapperTest.php in core/tests/Drupal/KernelTests/Core/File/StreamWrapperTest.php
system.install in core/modules/system/system.install
Install, update and uninstall functions for the system module.
system.module in core/modules/system/system.module
Configuration system that lets administrators modify the workings of the site.
TemporaryJsonapiFileFieldUploader.php in core/modules/jsonapi/src/Controller/TemporaryJsonapiFileFieldUploader.php
ThemeSettingsForm.php in core/modules/system/src/Form/ThemeSettingsForm.php
ToolkitGdTest.php in core/tests/Drupal/KernelTests/Core/Image/ToolkitGdTest.php
UpdatePathTestBase.php in core/tests/Drupal/FunctionalTests/Update/UpdatePathTestBase.php

Buggy or inaccurate documentation? Please file an issue. Need support? Need help programming? Connect with the Drupal community.