diff --git a/apps/file_manager/commands.cpp b/apps/file_manager/commands.cpp
index 425f88a..e407593 100644
--- a/apps/file_manager/commands.cpp
+++ b/apps/file_manager/commands.cpp
@@ -337,7 +337,7 @@ void CommandPasteTask(EsUserTask *userTask, EsGeneric _task) {
 
 		EsDirectoryChild information;
 
-		if (EsPathQueryInformation(STRING(source), &information)) {
+		if (ES_SUCCESS == EsPathQueryInformation(STRING(source), &information)) {
 			if (information.fileSize == -1) {
 				// TODO Support progress on volumes that don't report total directory sizes.
 			} else {
diff --git a/apps/file_manager/folder.cpp b/apps/file_manager/folder.cpp
index 5016ef5..df46230 100644
--- a/apps/file_manager/folder.cpp
+++ b/apps/file_manager/folder.cpp
@@ -17,7 +17,7 @@ Array<Folder *> foldersWithNoAttachedInstances;
 bool FSDirHandlesPath(String path) {
 	EsDirectoryChild information;
 
-	if (EsPathQueryInformation(STRING(path), &information)) {
+	if (ES_SUCCESS == EsPathQueryInformation(STRING(path), &information)) {
 		return information.type == ES_NODE_DIRECTORY;
 	} else {
 		return false;
@@ -91,7 +91,7 @@ EsError FSDirEnumerate(Folder *folder) {
 void FSDirGetTotalSize(Folder *folder) {
 	EsDirectoryChild information;
 
-	if (EsPathQueryInformation(STRING(folder->path), &information)) {
+	if (ES_SUCCESS == EsPathQueryInformation(STRING(folder->path), &information)) {
 		folder->spaceUsed = information.fileSize;
 		folder->spaceTotal = 0;
 	}
@@ -464,7 +464,7 @@ void FolderFileUpdatedAtPath(String path, Instance *instance) {
 	String file = PathGetName(path);
 	String folder = PathGetParent(path);
 	EsDirectoryChild information = {};
-	bool add = EsPathQueryInformation(STRING(path), &information);
+	bool add = ES_SUCCESS == EsPathQueryInformation(STRING(path), &information);
 
 	for (uintptr_t i = 0; i < loadedFolders.Length(); i++) {
 		if (loadedFolders[i]->itemHandler->type != NAMESPACE_HANDLER_FILE_SYSTEM) continue;
diff --git a/apps/script_console.cpp b/apps/script_console.cpp
index 353f68a..35017c0 100644
--- a/apps/script_console.cpp
+++ b/apps/script_console.cpp
@@ -378,8 +378,8 @@ int ExternalFileAppend(ExecutionContext *context, Value *returnValue) {
 int ExternalFileGetSize(ExecutionContext *context, Value *returnValue) {
 	STACK_POP_STRING(entryText, entryBytes);
 	EsDirectoryChild information;
-	bool exists = EsPathQueryInformation(entryText, entryBytes, &information);
-	if (!exists) RETURN_ERROR(ES_ERROR_FILE_DOES_NOT_EXIST);
+	EsError error = EsPathQueryInformation(entryText, entryBytes, &information);
+	if (error != ES_SUCCESS) RETURN_ERROR(ES_ERROR_FILE_DOES_NOT_EXIST);
 	if (information.type != ES_NODE_FILE) RETURN_ERROR(ES_ERROR_INCORRECT_NODE_TYPE);
 	returnValue->i = information.fileSize;
 	return EXTCALL_RETURN_ERR_UNMANAGED;
@@ -1011,7 +1011,7 @@ void EnterCommand(Instance *instance) {
 	uint8_t newline = '\n';
 	EsFileWriteSync(globalCommandHistoryFile.handle, EsFileGetSize(globalCommandHistoryFile.handle), dataBytes, data);
 	EsFileWriteSync(globalCommandHistoryFile.handle, EsFileGetSize(globalCommandHistoryFile.handle), 1, &newline);
-	EsFileControl(globalCommandHistoryFile.handle, ES_FILE_CONTROL_FLUSH); 
+	EsFileControl(globalCommandHistoryFile.handle, ES_FILE_CONTROL_FLUSH, nullptr, 0); 
 
 	EsPanel *commandLogRow = EsPanelCreate(instance->root, ES_CELL_H_FILL | ES_PANEL_STACK | ES_PANEL_HORIZONTAL, EsStyleIntern(&styleInputRow));
 	EsTextDisplayCreate(commandLogRow, ES_FLAGS_DEFAULT, EsStyleIntern(&stylePromptText), "\u2661");
diff --git a/boot/x86/esfs-stage2.s b/boot/x86/esfs-stage2.s
index 992e2c1..45e1646 100644
--- a/boot/x86/esfs-stage2.s
+++ b/boot/x86/esfs-stage2.s
@@ -132,7 +132,7 @@ LoadEachExtent:
 %endmacro
 
 %macro FilesystemSpecificCode 0
-KernelDataStreamPosition: dw 0x850
+KernelDataStreamPosition: dw 0x860
 ErrorBadFilesystem: db "Invalid boot EsFS volume.",0
 ErrorUnexpectedFileProblem: db "The kernel file could not be loaded.",0
 %endmacro
diff --git a/desktop/api.cpp b/desktop/api.cpp
index 2aaf7cc..f6c7aa1 100644
--- a/desktop/api.cpp
+++ b/desktop/api.cpp
@@ -1227,7 +1227,7 @@ void EsInstanceSaveComplete(EsInstance *instance, EsFileStore *file, bool succes
 	}
 
 	if (success) {
-		file->error = EsFileControl(file->handle, ES_FILE_CONTROL_FLUSH);
+		file->error = EsFileControl(file->handle, ES_FILE_CONTROL_FLUSH, nullptr, 0);
 
 		if (file->error != ES_SUCCESS) {
 			success = false;
diff --git a/desktop/api_tests.cpp b/desktop/api_tests.cpp
index dcf7264..52c7de5 100644
--- a/desktop/api_tests.cpp
+++ b/desktop/api_tests.cpp
@@ -1305,6 +1305,44 @@ bool ResizeFileTest() {
 
 //////////////////////////////////////////////////////////////
 
+bool FileContentTypeTest() {
+	int checkIndex = 0;
+	
+	EsUniqueIdentifier identifier1, identifier2;
+	for (uintptr_t i = 0; i < 16; i++) identifier1.d[i] = i;
+	for (uintptr_t i = 0; i < 16; i++) identifier2.d[i] = 0;
+
+	size_t fileSize;
+	uint32_t *fileData = (uint32_t *) EsFileReadAll(EsLiteral("|Settings:/continue.txt"), &fileSize);
+
+	if (fileData) {
+		size_t count;
+		EsError error;
+		EsDirectoryChild *array = EsDirectoryEnumerate(EsLiteral("|Settings:/test"), &count, &error);
+		CHECK(error == ES_SUCCESS);
+		CHECK(count == 1);
+		CHECK(0 == EsMemoryCompare(&identifier1, &array[0].contentType, sizeof(EsUniqueIdentifier)));
+		EsFileInformation information = EsFileOpen(EsLiteral("|Settings:/test/a"), ES_FILE_WRITE | ES_NODE_CREATE_DIRECTORIES);
+		CHECK(information.error == ES_SUCCESS);
+		CHECK(0 == EsMemoryCompare(&identifier1, &information.contentType, sizeof(EsUniqueIdentifier)));
+	} else {
+		uint32_t c = 1;
+		CHECK(ES_SUCCESS == EsFileWriteAll(EsLiteral("|Settings:/continue.txt"), &c, sizeof(uint32_t)));
+
+		EsFileInformation information = EsFileOpen(EsLiteral("|Settings:/test/a"), ES_FILE_WRITE | ES_NODE_CREATE_DIRECTORIES);
+		CHECK(information.error == ES_SUCCESS);
+		CHECK(0 == EsMemoryCompare(&identifier2, &information.contentType, sizeof(EsUniqueIdentifier)));
+		CHECK(ES_SUCCESS == EsFileControl(information.handle, ES_FILE_CONTROL_SET_CONTENT_TYPE, &identifier1, sizeof(identifier1)));
+
+		EsSyscall(ES_SYSCALL_SHUTDOWN, ES_SHUTDOWN_ACTION_RESTART, 0, 0, 0);
+		while (EsMessageReceive());
+	}
+
+	return true;
+}
+
+//////////////////////////////////////////////////////////////
+
 #endif
 
 const Test tests[] = {
@@ -1323,6 +1361,7 @@ const Test tests[] = {
 	TEST(POSIXSubsystemTest, 120),
 	TEST(RestartTest, 1200),
 	TEST(ResizeFileTest, 600),
+	TEST(FileContentTypeTest, 60),
 };
 
 #ifndef API_TESTS_FOR_RUNNER
diff --git a/desktop/files.cpp b/desktop/files.cpp
index 0505a0a..aee47ae 100644
--- a/desktop/files.cpp
+++ b/desktop/files.cpp
@@ -71,16 +71,17 @@ bool EsPathExists(const char *path, ptrdiff_t pathBytes, EsNodeType *type) {
 	return true;
 }
 
-bool EsPathQueryInformation(const char *path, ptrdiff_t pathBytes, EsDirectoryChild *information) {
+EsError EsPathQueryInformation(const char *path, ptrdiff_t pathBytes, EsDirectoryChild *information) {
 	if (pathBytes == -1) pathBytes = EsCStringLength(path);
 	_EsNodeInformation node = {};
 	EsError error = NodeOpen(path, pathBytes, ES_NODE_FAIL_IF_NOT_FOUND, &node);
-	if (error != ES_SUCCESS) return false;
+	if (error != ES_SUCCESS) return error;
 	EsHandleClose(node.handle);
 	information->type = node.type;
 	information->fileSize = node.fileSize;
 	information->directoryChildren = node.directoryChildren;
-	return true;
+	information->contentType = node.contentType;
+	return ES_SUCCESS;
 }
 
 EsError EsPathCreate(const char *path, ptrdiff_t pathBytes, EsNodeType type, bool createLeadingDirectories) {
@@ -94,8 +95,8 @@ EsError EsPathCreate(const char *path, ptrdiff_t pathBytes, EsNodeType type, boo
 	return ES_SUCCESS;
 }
 
-EsError EsFileControl(EsHandle file, uint32_t flags) {
-	return EsSyscall(ES_SYSCALL_FILE_CONTROL, file, flags, 0, 0);
+EsError EsFileControl(EsHandle file, EsFileControlOperation operation, const void *data, size_t dataBytes) {
+	return EsSyscall(ES_SYSCALL_FILE_CONTROL, file, operation, (uintptr_t) data, dataBytes);
 }
 
 ptrdiff_t DirectoryEnumerateFromHandle(EsHandle directory, EsDirectoryChild *buffer, size_t size) {
@@ -167,6 +168,7 @@ EsFileInformation EsFileOpen(const char *path, ptrdiff_t pathLength, uint32_t fl
 	if (result == ES_SUCCESS) {
 		information.handle = node.handle;
 		information.size = node.fileSize;
+		information.contentType = node.contentType;
 	}
 
 	information.error = result;
@@ -245,7 +247,7 @@ EsFileOffsetDifference EsFileStoreGetSize(EsFileStore *file) {
 	} else if (file->type == FILE_STORE_PATH) {
 		EsDirectoryChild information;
 
-		if (EsPathQueryInformation(file->path, file->pathBytes, &information)) {
+		if (ES_SUCCESS == EsPathQueryInformation(file->path, file->pathBytes, &information)) {
 			return file->pathBytes;
 		} else {
 			return -1;
@@ -576,7 +578,7 @@ EsError EsFileWriteAllGatherFromHandle(EsHandle handle, const void **data, const
 		offset += sizes[i];
 	}
 
-	error = EsFileControl(handle, ES_FILE_CONTROL_FLUSH);
+	error = EsFileControl(handle, ES_FILE_CONTROL_FLUSH, nullptr, 0);
 	return error;
 }
 
diff --git a/desktop/os.header b/desktop/os.header
index 204986f..05cb15a 100644
--- a/desktop/os.header
+++ b/desktop/os.header
@@ -760,8 +760,9 @@ inttype EsConnectionOpenFlags uint32_t none {
 	ES_CONNECTION_OPEN_WAIT = bit 0
 };
 
-inttype EsFileControlFlags uint32_t none {
-	ES_FILE_CONTROL_FLUSH = bit 0
+inttype EsFileControlOperation uint32_t none {
+	ES_FILE_CONTROL_FLUSH = 0 // data/dataBytes ignored
+	ES_FILE_CONTROL_SET_CONTENT_TYPE = 1 // data EsUniqueIdentifier; dataBytes ignored
 };
 
 inttype EsElementUpdateContentFlags uint32_t none {
@@ -838,6 +839,7 @@ inttype EsProcessCreationFlags uint32_t none {
 
 inttype EsVolumeFlags uint32_t none {
 	ES_VOLUME_READ_ONLY = bit 0
+	ES_VOLUME_STORES_CONTENT_TYPE = bit 1
 };
 
 inttype EsPathMoveFlags uint32_t none {
@@ -1340,6 +1342,7 @@ struct EsFileInformation {
 	EsHandle handle; 
 	EsFileOffset size;
 	EsError error;
+	EsUniqueIdentifier contentType; // Zeroed if unsupported, or not initialised.
 };
 
 struct EsDirectoryChild {
@@ -1348,6 +1351,7 @@ struct EsDirectoryChild {
 	EsNodeType type;
 	EsFileOffsetDifference fileSize; // -1 if unsupported.
 	EsFileOffsetDifference directoryChildren; // ES_DIRECTORY_CHILDREN_UNKNOWN if unsupported.
+	EsUniqueIdentifier contentType; // Zeroed if unsupported, or not initialised.
 };
 
 struct EsPoint {
@@ -1635,6 +1639,7 @@ private struct _EsNodeInformation {
 	EsFileOffset fileSize;
 	EsFileOffsetDifference directoryChildren; 
 	EsNodeType type;
+	EsUniqueIdentifier contentType;
 };
 
 struct EsVolumeInformation {
@@ -2137,7 +2142,7 @@ function EsError EsFileWriteAllGatherFromHandle(EsHandle handle, const void **da
 function void *EsFileMap(STRING filePath, size_t *fileSize, uint32_t flags) @native();
 function EsError EsFileCopy(STRING source, STRING destination, void **copyBuffer = ES_NULL, EsFileCopyCallback callback = ES_NULL, EsGeneric data = ES_NULL) @todo(); // If you are copying lots of files, you can reuse the temporary copy buffer by storing the output copyBuffer; call EsHeapFree on it after the last copy.
 
-function EsError EsFileControl(EsHandle file, EsFileControlFlags flags); 
+function EsError EsFileControl(EsHandle file, EsFileControlOperation operation, const void *data, size_t dataBytes) @buffer_in(data, dataBytes); 
 function EsFileInformation EsFileOpen(STRING path, EsFileOpenFlags flags);
 function EsFileOffset EsFileGetSize(EsHandle handle);
 function size_t EsFileReadSync(EsHandle file, EsFileOffset offset, size_t size, void *buffer) @buffer_out(buffer, size);
@@ -2150,7 +2155,7 @@ function size_t EsPathFindUniqueName(char *buffer, size_t originalBytes, size_t
 function EsError EsPathMove(STRING oldPath, STRING newPath, EsPathMoveFlags flags = ES_FLAGS_DEFAULT);
 function bool EsPathExists(STRING filePath, EsNodeType *type = ES_NULL) @out(type); // Returns true if the file/directory exists.
 function EsError EsPathCreate(STRING filePath, EsNodeType type, bool createLeadingDirectories);
-function bool EsPathQueryInformation(STRING filePath, EsDirectoryChild *information) @out(information);
+function EsError EsPathQueryInformation(STRING filePath, EsDirectoryChild *information) @out(information);
 
 function void *EsFileStoreReadAll(EsFileStore *file, size_t *fileSize) @heap_buffer_out(return, fileSize*) @out(fileSize); // Free with EsHeapFree.
 function bool EsFileStoreWriteAll(EsFileStore *file, const void *data, size_t dataBytes) @buffer_in(data, dataBytes);
diff --git a/drivers/esfs2.cpp b/drivers/esfs2.cpp
index f597624..c40283c 100644
--- a/drivers/esfs2.cpp
+++ b/drivers/esfs2.cpp
@@ -9,7 +9,6 @@
 
 // TODO Calling FSDirectoryEntryFound on all directory entries seen during scanning, even if they're not the target.
 // TODO Informing the block cache when a directory is truncated and its extents are freed.
-// TODO Renaming directories does not work?
 // TODO ESFS_CHECK_XXX are used to report out of memory errors, which shouldn't report KERNEL_PROBLEM_DAMAGED_FILESYSTEM.
 
 #define ESFS_CHECK(x, y)                 if (!(x)) { KernelLog(LOG_ERROR, "EsFS", "damaged file system", y "\n"); return false; }
@@ -342,6 +341,9 @@ static void Sync(KNode *_directory, KNode *node) {
 		// Get the most recent totalSize for the directory.
 		AttributeDirectory *directoryAttribute = (AttributeDirectory *) FindAttribute(&file->entry, ESFS_ATTRIBUTE_DIRECTORY);
 		directoryAttribute->totalSize = FSNodeGetTotalSize(node);
+	} else if (file->type == ES_NODE_FILE) {
+		// Get the most recent contentType for the file.
+		file->entry.contentType = FSNodeGetContentType(node);
 	}
 
 	{
@@ -422,6 +424,7 @@ static EsError Enumerate(KNode *node) {
 				}
 			} else if (metadata.type == ES_NODE_FILE) {
 				metadata.totalSize = entry->fileSize;
+				metadata.contentType = entry->contentType;
 			}
 
 			EsError error = FSDirectoryEntryFound(node, &metadata, &reference, 
@@ -1819,6 +1822,7 @@ static EsError Scan(const char *name, size_t nameLength, KNode *_directory) {
 		}
 	} else {
 		metadata.totalSize = entry->fileSize;
+		metadata.contentType = entry->contentType;
 	}
 
 	metadata.type = entry->nodeType == ESFS_NODE_TYPE_DIRECTORY ? ES_NODE_DIRECTORY : ES_NODE_FILE;
@@ -2009,6 +2013,7 @@ static void Register(KDevice *_parent) {
 	volume->rootDirectoryInitialChildren = rootDirectoryChildren;
 	volume->directoryEntryDataBytes = sizeof(DirectoryEntryReference);
 	volume->nodeDataBytes = sizeof(FSNode);
+	volume->volumeFlags |= ES_VOLUME_STORES_CONTENT_TYPE;
 
 	FSRegisterBootFileSystem(volume, volume->superblock.osInstallation);
 }
diff --git a/kernel/files.cpp b/kernel/files.cpp
index f9cdc78..2b0c629 100644
--- a/kernel/files.cpp
+++ b/kernel/files.cpp
@@ -67,7 +67,8 @@ EsError FSNodeDelete(KNode *node);
 EsError FSNodeMove(KNode *node, KNode *destination, const char *newName, size_t nameNameBytes);
 EsError FSFileResize(KNode *node, EsFileOffset newSizeBytes);
 ptrdiff_t FSDirectoryEnumerate(KNode *node, K_USER_BUFFER EsDirectoryChild *buffer, size_t bufferSize);
-EsError FSFileControl(KNode *node, uint32_t flags);
+EsError FSFileControlFlush(KNode *node);
+EsError FSFileControlSetContentType(KNode *node, EsUniqueIdentifier identifier);
 bool FSTrimCachedNode(MMObjectCache *);
 bool FSTrimCachedDirectoryEntry(MMObjectCache *);
 EsError FSBlockDeviceAccess(KBlockDeviceAccessRequest request);
@@ -96,6 +97,10 @@ EsFileOffset FSNodeGetTotalSize(KNode *node) {
 	return node->directoryEntry->totalSize;
 }
 
+EsUniqueIdentifier FSNodeGetContentType(KNode *node) {
+	return node->directoryEntry->contentType;
+}
+
 char *FSNodeGetName(KNode *node, size_t *bytes) {
 	KWriterLockAssertLocked(&node->writerLock);
 	*bytes = node->directoryEntry->item.key.longKeyBytes;
@@ -381,42 +386,52 @@ ptrdiff_t FSFileWriteSync(KNode *node, K_USER_BUFFER const void *buffer, EsFileO
 	return error == ES_SUCCESS ? bytes : error;
 }
 
-EsError FSFileControl(KNode *node, uint32_t flags) {
+EsError FSFileControlFlush(KNode *node) {
 	FSFile *file = (FSFile *) node;
 
-	if (flags & ES_FILE_CONTROL_FLUSH) {
-		KWriterLockTake(&file->resizeLock, K_LOCK_EXCLUSIVE);
-		EsDefer(KWriterLockReturn(&file->resizeLock, K_LOCK_EXCLUSIVE));
+	KWriterLockTake(&file->resizeLock, K_LOCK_EXCLUSIVE);
+	EsDefer(KWriterLockReturn(&file->resizeLock, K_LOCK_EXCLUSIVE));
 
-		CCSpaceFlush(&file->cache);
+	CCSpaceFlush(&file->cache);
 
-		KWriterLockTake(&file->writerLock, K_LOCK_EXCLUSIVE);
-		EsDefer(KWriterLockReturn(&file->writerLock, K_LOCK_EXCLUSIVE));
+	KWriterLockTake(&file->writerLock, K_LOCK_EXCLUSIVE);
+	EsDefer(KWriterLockReturn(&file->writerLock, K_LOCK_EXCLUSIVE));
 
-		__sync_fetch_and_and(&file->flags, ~NODE_MODIFIED);
+	__sync_fetch_and_and(&file->flags, ~NODE_MODIFIED);
 
-		EsError error = FSFileCreateAndResizeOnFileSystem(file, file->directoryEntry->totalSize);
-		if (error != ES_SUCCESS) return error;
+	EsError error = FSFileCreateAndResizeOnFileSystem(file, file->directoryEntry->totalSize);
+	if (error != ES_SUCCESS) return error;
 
-		if (file->fileSystem->sync) {
-			// TODO Should we also sync the parent?
-			FSDirectory *parent = file->directoryEntry->parent;
+	if (file->fileSystem->sync) {
+		// TODO Should we also sync the parent?
+		FSDirectory *parent = file->directoryEntry->parent;
 
-			if (parent) KWriterLockTake(&parent->writerLock, K_LOCK_EXCLUSIVE);
-			file->fileSystem->sync(parent, file);
-			if (parent) KWriterLockReturn(&parent->writerLock, K_LOCK_EXCLUSIVE);
-		}
+		if (parent) KWriterLockTake(&parent->writerLock, K_LOCK_EXCLUSIVE);
+		file->fileSystem->sync(parent, file);
+		if (parent) KWriterLockReturn(&parent->writerLock, K_LOCK_EXCLUSIVE);
+	}
 
-		if (file->error != ES_SUCCESS) {
-			EsError error = file->error;
-			file->error = ES_SUCCESS;
-			return error;
-		}
+	if (file->error != ES_SUCCESS) {
+		EsError error = file->error;
+		file->error = ES_SUCCESS;
+		return error;
 	}
 
 	return ES_SUCCESS;
 }
 
+EsError FSFileControlSetContentType(KNode *node, EsUniqueIdentifier identifier) {
+	if (node->fileSystem->flags & ES_VOLUME_READ_ONLY) {
+		return ES_ERROR_FILE_ON_READ_ONLY_VOLUME;
+	} else if (~node->fileSystem->flags & ES_VOLUME_STORES_CONTENT_TYPE) {
+		return ES_ERROR_UNSUPPORTED;
+	} else {
+		node->directoryEntry->contentType = identifier;
+		__sync_fetch_and_or(&node->flags, NODE_MODIFIED); // Set the modified flag *after* making the modification.
+		return ES_SUCCESS;
+	}
+}
+
 //////////////////////////////////////////
 // Directories.
 //////////////////////////////////////////
@@ -669,6 +684,7 @@ void _FSDirectoryEnumerateVisit(AVLItem<FSDirectoryEntry> *item, K_USER_BUFFER E
 	output->fileSize = entry->totalSize;
 	output->directoryChildren = entry->directoryChildren;
 	output->nameBytes = nameBytes;
+	output->contentType = entry->contentType;
 
 	_FSDirectoryEnumerateVisit(item->children[0], buffer, bufferSize, position);
 	_FSDirectoryEnumerateVisit(item->children[1], buffer, bufferSize, position);
@@ -808,9 +824,6 @@ EsError FSNodeCreate(FSDirectory *parent, const char *name, size_t nameBytes, Es
 		parent->directoryEntry->directoryChildren++;
 	}
 
-	__sync_fetch_and_or(&parent->flags, NODE_MODIFIED);
-	__sync_fetch_and_or(&node->flags, NODE_MODIFIED);
-	
 	// Only create directories immediately; files are created in FSWriteFromCache.
 
 	if (type != ES_NODE_FILE) {
@@ -823,6 +836,10 @@ EsError FSNodeCreate(FSDirectory *parent, const char *name, size_t nameBytes, Es
 		}
 	}
 
+	// Set the modified flag *after* making the modification.
+	__sync_fetch_and_or(&parent->flags, NODE_MODIFIED);
+	__sync_fetch_and_or(&node->flags, NODE_MODIFIED);
+	
 	// Put the node onto the object cache list.
 	// Since the parent directory is locked, it should stay around for long enough to be immediately found FSNodeTraverseLayer.
 	if (node->flags & NODE_IN_CACHE_LIST) KernelPanic("FSNodeCreate - Node %x is already in the cache list.\n", node);
@@ -1888,6 +1905,7 @@ void FSTrackUserFileSystemHandle(KDevice *device, bool opened) {
 }
 
 void FSRegisterFileSystem(KFileSystem *fileSystem) {
+	if (!fileSystem->write) fileSystem->volumeFlags |= ES_VOLUME_READ_ONLY;
 	fileSystem->trackHandle = FSTrackUserFileSystemHandle;
 	MMObjectCacheRegister(&fileSystem->cachedDirectoryEntries, FSTrimCachedDirectoryEntry, 
 			sizeof(FSDirectoryEntry) + 16 /* approximate average name bytes */ + fileSystem->directoryEntryDataBytes);
diff --git a/kernel/module.h b/kernel/module.h
index d48bf7b..6e0ad50 100644
--- a/kernel/module.h
+++ b/kernel/module.h
@@ -805,6 +805,7 @@ struct KNodeMetadata {
 	bool removingNodeFromCache, removingThisFromCache;
 	EsFileOffset totalSize;
 	EsFileOffsetDifference directoryChildren; // ES_DIRECTORY_CHILDREN_UNKNOWN if not supported by the file system.
+	EsUniqueIdentifier contentType;
 };
 
 struct KNode {
@@ -840,6 +841,8 @@ struct KFileSystem : KDevice {
 	char name[64];
 	size_t nameBytes;
 
+	EsVolumeFlags volumeFlags; // Note: ES_VOLUME_READ_ONLY will be automatically set if you don't set the write() callback pointer.
+
 	size_t directoryEntryDataBytes; // The size of the driverData passed to FSDirectoryEntryFound and received in the load callback.
 	size_t nodeDataBytes; // The average bytes allocated by the driver per node (used for managing cache sizes).
 
@@ -906,6 +909,7 @@ struct KNodeInformation {
 KNodeInformation FSNodeOpen(const char *path, size_t pathBytes, uint32_t flags, KNode *baseDirectory = nullptr);
 
 EsFileOffset FSNodeGetTotalSize(KNode *node);
+EsUniqueIdentifier FSNodeGetContentType(KNode *node);
 
 char *FSNodeGetName(KNode *node, size_t *bytes); // For debugging use only.
 
diff --git a/kernel/syscall.cpp b/kernel/syscall.cpp
index d50d518..33e9e70 100644
--- a/kernel/syscall.cpp
+++ b/kernel/syscall.cpp
@@ -628,7 +628,7 @@ SYSCALL_IMPLEMENT(ES_SYSCALL_VOLUME_GET_INFORMATION) {
 	information.spaceUsed = fileSystem->spaceUsed;
 	information.spaceTotal = fileSystem->spaceTotal;
 	information.id = fileSystem->objectID;
-	information.flags = fileSystem->write ? ES_FLAGS_DEFAULT : ES_VOLUME_READ_ONLY;
+	information.flags = fileSystem->volumeFlags;
 	information.installationIdentifier = fileSystem->installationIdentifier;
 	information.identifier = fileSystem->identifier;
 
@@ -702,6 +702,7 @@ SYSCALL_IMPLEMENT(ES_SYSCALL_NODE_OPEN) {
 	information.type = _information.node->directoryEntry->type;
 	information.fileSize = _information.node->directoryEntry->totalSize;
 	information.directoryChildren = _information.node->directoryEntry->directoryChildren;
+	information.contentType = _information.node->directoryEntry->contentType;
 	information.handle = currentProcess->handleTable.OpenHandle(_information.node, flags, KERNEL_OBJECT_NODE);
 	SYSCALL_WRITE(argument3, &information, sizeof(_EsNodeInformation));
 
@@ -1187,13 +1188,26 @@ SYSCALL_IMPLEMENT(ES_SYSCALL_DIRECTORY_ENUMERATE) {
 }
 
 SYSCALL_IMPLEMENT(ES_SYSCALL_FILE_CONTROL) {
-	SYSCALL_HANDLE(argument0, KERNEL_OBJECT_NODE, file, KNode);
+	SYSCALL_HANDLE_2(argument0, KERNEL_OBJECT_NODE, handle);
+	KNode *file = (KNode *) handle.object; 
 
 	if (file->directoryEntry->type != ES_NODE_FILE) {
 		SYSCALL_RETURN(ES_FATAL_ERROR_INCORRECT_NODE_TYPE, true);
+	} else if ((handle.flags & (ES_FILE_WRITE_SHARED | ES_FILE_WRITE)) == 0) {
+		SYSCALL_RETURN(ES_FATAL_ERROR_INCORRECT_FILE_ACCESS, true);
 	}
 
-	SYSCALL_RETURN(FSFileControl(file, argument1), false);
+	EsError error = ES_ERROR_UNSUPPORTED;
+
+	if (argument1 == ES_FILE_CONTROL_FLUSH) {
+		error = FSFileControlFlush(file);
+	} else if (argument1 == ES_FILE_CONTROL_SET_CONTENT_TYPE) {
+		EsUniqueIdentifier identifier;
+		SYSCALL_READ(&identifier, argument2, sizeof(identifier));
+		error = FSFileControlSetContentType(file, identifier);
+	}
+
+	SYSCALL_RETURN(error, false);
 }
 
 SYSCALL_IMPLEMENT(ES_SYSCALL_BATCH) {
diff --git a/shared/esfs2.h b/shared/esfs2.h
index ce7a491..56c3005 100644
--- a/shared/esfs2.h
+++ b/shared/esfs2.h
@@ -111,9 +111,10 @@ typedef struct DirectoryEntry {
 	/* 32 */ uint64_t creationTime, accessTime, modificationTime;	// Timekeeping. In microseconds since 1st January 1970.
 	/* 56 */ uint64_t fileSize;					// The amount of data referenced by the data attribute in bytes.
 	/* 64 */ EsUniqueIdentifier parent;				// Identifier of the parent directory.
+	/* 80 */ EsUniqueIdentifier contentType;                        // Identifier of the file content type.
 
-#define ESFS_ATTRIBUTE_OFFSET (80)
-	/* 80 */ uint8_t attributes[1024 - ESFS_ATTRIBUTE_OFFSET];	// Attribute list.
+#define ESFS_ATTRIBUTE_OFFSET (96)
+	/* 96 */ uint8_t attributes[1024 - ESFS_ATTRIBUTE_OFFSET];	// Attribute list.
 } DirectoryEntry;
 
 typedef struct GroupDescriptor {
diff --git a/util/build.c b/util/build.c
index f88eb90..fe7741c 100644
--- a/util/build.c
+++ b/util/build.c
@@ -59,6 +59,7 @@ FILE *systemLog;
 char compilerPath[4096];
 int argc;
 char **argv;
+bool runningTests;
 
 #ifndef PATH_MAX
 #define PATH_MAX 1024
@@ -985,13 +986,17 @@ void BuildAndRun(int optimise, bool compile, int debug, int emulator, int log) {
 		Run(emulator, log, debug);
 	}
 
-	exit(encounteredErrors ? 1 : 0);
+	if (!runningTests) {
+		exit(encounteredErrors ? 1 : 0);
+	}
 }
 
 void RunTests(int singleTest) {
 	// TODO Capture emulator memory dump if a test causes a EsPanic.
 	// TODO Using SMP/KVM if available in the optimised test runs.
 
+	runningTests = true;
+
 	int successCount = 0, failureCount = 0;
 	CallSystem("mkdir -p root/Essence/Settings/API\\ Tests");
 	FILE *testFailures = fopen("bin/Logs/Test Failures.txt", "wb");
diff --git a/util/start.script b/util/start.script
index 29aafc0..4a4b53c 100644
--- a/util/start.script
+++ b/util/start.script
@@ -15,6 +15,10 @@ str compilerPath #persist;
 int compilerIndex #persist;
 bool runningMakefiles #persist;
 
+/////////////////////////////////////////////////////////////
+// Environment setup
+/////////////////////////////////////////////////////////////
+
 void Setup(bool forAutomation) {
 	assert PersistRead("bin/start.script.persist");
 
@@ -109,6 +113,10 @@ void Setup(bool forAutomation) {
 	}
 }
 
+/////////////////////////////////////////////////////////////
+// Command interface
+/////////////////////////////////////////////////////////////
+
 void DoCommand(str command) {
 	if command == "line-count" {
 		int count = 0;
@@ -215,6 +223,10 @@ void Start() {
 	}
 }
 
+/////////////////////////////////////////////////////////////
+// Automation scripts
+/////////////////////////////////////////////////////////////
+
 void GenerateOVF() {
 	str[] template = StringSplitByCharacter(FileReadAll("util/template.ovf"):assert(), "$", true);
 	assert template:len() == 5;