Навигация по файловой системе File System Navigation

Заголовок реализует техническую спецификацию файловой системы C++ ISO/IEC TS 18822:2015 (окончательный вариант черновика: ISO/IEC JTC 1/SC 22/WG 21 N4100) и имеет типы и функции, позволяющие создавать независимый от платформы код для навигации по файловой системе. The header implements the C++ File System Technical Specification ISO/IEC TS 18822:2015 (Final draft: ISO/IEC JTC 1/SC 22/WG 21 N4100) and has types and functions that enable you to write platform-independent code for navigating the file system. Поскольку это межплатформенное приложение, оно содержит интерфейсы API, не относящиеся к системам Windows. Because it’s cross-platform, it contains APIs that aren’t relevant for Windows systems. Например, is_fifo(const path&) всегда возвращает значение false в Windows. For example, is_fifo(const path&) always returns false on Windows.

Обзор Overview

Используйте API для следующих задач: Use the APIs for the following tasks:

выполнение итерации по файлам и каталогам в указанном пути; iterate over files and directories under a specified path

получение сведений о файлах, включая время создания, размер, расширение и корневой каталог; get information about files including the time created, size, extension, and root directory

составление, разделение и сравнение путей; compose, decompose, and compare paths

Создание, копирование и удаление каталогов create, copy, and delete directories

копирование и удаление файлов. copy and delete files

Дополнительные сведения о вводе-выводе файлов с помощью стандартной библиотеки см. в разделе Программирование iostream. For more information about File IO using the Standard Library, see iostream Programming.

Пути Paths

Создание и составление путей Constructing and composing paths

Пути в Windows (начиная с XP) изначально хранятся в Юникоде. Paths in Windows (since XP) are stored natively in Unicode. path Класс автоматически выполняет все необходимые преобразования строк. The path class automatically does all necessary string conversions. Он принимает аргументы как для широких, так и для узких символьных массивов, а также для std::string std::wstring типов, отформатированных как UTF8 или UTF16. It accepts arguments of both wide and narrow character arrays, and both std::string and std::wstring types formatted as UTF8 or UTF16. Класс path также автоматически нормализует разделители путей. The path class also automatically normalizes path separators. В аргументах конструктора в качестве разделителя каталогов можно использовать одиночную косую черту. You can use a single forward slash as a directory separator in constructor arguments. Этот разделитель позволяет использовать одни и те же строки для хранения путей в средах Windows и UNIX: This separator lets you use the same strings to store paths in both Windows and UNIX environments:

Для объединения двух путей можно использовать перегруженные операторы / и /= , которые аналогичны операторам + и += в std::string и std::wstring . To concatenate two paths, you can use the overloaded / and /= operators, which are analogous to the + and += operators on std::string and std::wstring . path Объект будет удобным образом предоставлять разделители, если это не так. The path object will conveniently supply the separators if you don’t.

Проверка путей Examining paths

Класс Path имеет несколько методов, возвращающих сведения о различных частях пути. The path class has several methods that return information about various parts of the path itself. Эта информация отличается от сведений о сущности файловой системы, на которую может ссылаться. This information is distinct from the information about the file system entity it might refer to. Можно получить корень, относительный путь, имя файла, расширение файла и другие сведения. You can get the root, the relative path, the file name, the file extension, and more. Можно выполнять итерацию по объекту path для проверки всех папок в иерархии. You can iterate over a path object to examine all the folders in the hierarchy. В следующем примере показано, как выполнить итерацию по объекту пути. The following example shows how to iterate over a path object. И, как получить сведения о его частях. And, how to retrieve information about its parts.

Код создает следующие выходные данные: The code produces this output:

Сравнение путей Comparing paths

Класс path перегружает операторы сравнения на равенство как std::string и std::wstring . The path class overloads the same comparison operators as std::string and std::wstring . При сравнении двух путей необходимо выполнить сравнение строк после нормализации разделителей. When you compare two paths, you make a string comparison after the separators have been normalized. Если пропущена Замыкающая косая черта (или обратная косая черта), она не добавляется и влияет на сравнение. If a trailing slash (or backslash) is missing, it isn’t added, and that affects the comparison. В следующем примере показано, как выполняется сравнение значений пути: The following example demonstrates how path values compare:

Для запуска этого кода вставьте его в полный пример выше перед main и раскомментируйте строку, которая вызывает его в основном объекте. To run this code, paste it into the full example above before main and uncomment the line that calls it in main.

Преобразование между типами пути и строки Converting between path and string types

Объект path может быть неявно преобразован в std::wstring или std::string . A path object is implicitly convertible to std::wstring or std::string . Это означает, что можно передать путь к таким функциям wofstream::open , как, как показано в следующем примере: It means you can pass a path to functions such as wofstream::open , as shown in this example:

Итерация по каталогам и файлам Iterating directories and files

Заголовок предоставляет directory_iterator тип для итерации по отдельным каталогам и recursive_directory_iterator класс для рекурсивного прохода по каталогу и его подкаталогам. The header provides the directory_iterator type to iterate over single directories, and the recursive_directory_iterator class to iterate recursively over a directory and its subdirectories. После создания итератора путем передачи ему объекта path итератор указывает на первое значение directory_entry в пути. After you construct an iterator by passing it a path object, the iterator points to the first directory_entry in the path. Создайте конечный итератор путем вызова конструктора по умолчанию. Create the end iterator by calling the default constructor.

При итерации по каталогу существует несколько типов элементов, которые можно обнаружить. When iterating through a directory, there are several kinds of items you might discover. К этим элементам относятся каталоги, файлы, символические ссылки, файлы сокетов и др. These items include directories, files, symbolic links, socket files, and others. directory_iterator Возвращает свои элементы в виде directory_entry объектов. The directory_iterator returns its items as directory_entry objects.

File systems

In computing, a file system or filesystem controls how data is stored and retrieved. Without a file system, information placed in a storage medium would be one large body of data with no way to tell where one piece of information stops and the next begins. By separating the data into pieces and giving each piece a name, the information is easily isolated and identified. Taking its name from the way paper-based information systems are named, each group of data is called a «file». The structure and logic rules used to manage the groups of information and their names is called a «file system».

Individual drive partitions can be setup using one of the many different available filesystems. Each has its own advantages, disadvantages, and unique idiosyncrasies. A brief overview of supported filesystems follows; the links are to Wikipedia pages that provide much more information.

Contents

Types of file systems

The factual accuracy of this article or section is disputed.

See filesystems(5) for a general overview and Wikipedia:Comparison of file systems for a detailed feature comparison. File systems supported by the kernel are listed in /proc/filesystems .

In-tree and FUSE file systems

File system	Creation command	Userspace utilities	Archiso [1]	Kernel documentation [2][3]	Notes
Btrfs	mkfs.btrfs(8)	btrfs-progs	Yes	btrfs.html	Stability status
VFAT	mkfs.fat(8)	dosfstools	Yes	vfat.html	Windows 9x file system
exFAT	mkfs.exfat(8)	exfatprogs	Yes	Native file system in Linux 5.4. [4]
	mkexfatfs(8)	exfat-utils	No	N/A (FUSE-based)
F2FS	mkfs.f2fs(8)	f2fs-tools	Yes	f2fs.html	Flash-based devices
ext3	mke2fs(8)	e2fsprogs	Yes	ext3.html
ext4	mke2fs(8)	e2fsprogs	Yes	ext4.html
HFS	mkfs.hfsplus(8)	hfsprogs AUR	No	hfs.html	Classic Mac OS file system
HFS+	mkfs.hfsplus(8)	hfsprogs AUR	No	hfsplus.html	macOS (8–10.12) file system
JFS	mkfs.jfs(8)	jfsutils	Yes	jfs.txt
NILFS2	mkfs.nilfs2(8)	nilfs-utils	Yes	nilfs2.html	Raw flash devices, e.g. SD card
NTFS	mkfs.ntfs(8)	ntfs-3g	Yes	N/A (FUSE-based)	Windows NT file system
ReiserFS	mkfs.reiserfs(8)	reiserfsprogs	Yes
UDF	mkfs.udf(8)	udftools	Yes	udf.html
XFS	mkfs.xfs(8)	xfsprogs	Yes

Out-of-tree file systems

File system	Creation command	Kernel patchset	Userspace utilities	Notes
APFS	mkapfs(8)	linux-apfs-dkms-git AUR	apfsprogs-git AUR	macOS (10.13 and newer) file system. Read only, experimental.
Bcachefs	bcachefs(8)	linux-bcachefs-git AUR	bcachefs-tools-git AUR
NTFS	ntfs3-dkms AUR	Paragon NTFS3 driver FAQ
Reiser4	mkfs.reiser4(8)	reiser4progs AUR
ZFS	zfs-linux AUR , zfs-dkms AUR	zfs-utils AUR	OpenZFS port

Journaling

All the above filesystems with the exception of exFAT, ext2, FAT16/32, Reiser4 (optional), Btrfs and ZFS, use journaling. Journaling provides fault-resilience by logging changes before they are committed to the filesystem. In the event of a system crash or power failure, such file systems are faster to bring back online and less likely to become corrupted. The logging takes place in a dedicated area of the filesystem.

Not all journaling techniques are the same. Ext3 and ext4 offer data-mode journaling, which logs both data and meta-data, as well as possibility to journal only meta-data changes. Data-mode journaling comes with a speed penalty and is not enabled by default. In the same vein, Reiser4 offers so-called «transaction models» which not only change the features it provides, but in its journaling mode. It uses a different journaling techniques: a special model called wandering logs which eliminates the need to write to the disk twice, write-anywhere—a pure copy-on-write approach (mostly equivalent to btrfs’ default but with a fundamentally different «tree» design) and a combined approach called hybrid which heuristically alternates between the two former.

The other filesystems provide ordered-mode journaling, which only logs meta-data. While all journaling will return a filesystem to a valid state after a crash, data-mode journaling offers the greatest protection against corruption and data loss. There is a compromise in system performance, however, because data-mode journaling does two write operations: first to the journal and then to the disk (which Reiser4 avoids with its «wandering logs» feature). The trade-off between system speed and data safety should be considered when choosing the filesystem type. Reiser4 is the only filesystem that by design operates on full atomicity and also provides checksums for both meta-data and inline data (operations entirely occur, or they entirely do not and does not corrupt or destroy data due to operations half-occurring) and by design is therefore much less prone to data loss than other file systems like Btrfs.

Filesystems based on copy-on-write (also known as write-anywhere), such as Reiser4, Btrfs and ZFS, have no need to use traditional journal to protect metadata, because they are never updated in-place. Although Btrfs still has a journal-like log tree, it is only used to speed-up fdatasync/fsync.

FUSE-based file systems

Stackable file systems

• aufs — Advanced Multi-layered Unification Filesystem, a FUSE based union filesystem, a complete rewrite of Unionfs, was rejected from Linux mainline and instead OverlayFS was merged into the Linux Kernel.

http://aufs.sourceforge.net || linux-aufsAUR

• eCryptfs — The Enterprise Cryptographic Filesystem is a package of disk encryption software for Linux. It is implemented as a POSIX-compliant filesystem-level encryption layer, aiming to offer functionality similar to that of GnuPG at the operating system level.

http://ecryptfs.org || ecryptfs-utils

• mergerfs — a FUSE based union filesystem.

https://github.com/trapexit/mergerfs || mergerfsAUR

• mhddfs — Multi-HDD FUSE filesystem, a FUSE based union filesystem.

http://mhddfs.uvw.ru || mhddfsAUR

• overlayfs — OverlayFS is a filesystem service for Linux which implements a union mount for other file systems.

https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html || linux

• Unionfs — Unionfs is a filesystem service for Linux, FreeBSD and NetBSD which implements a union mount for other file systems.

http://unionfs.filesystems.org/ || not packaged? search in AUR

• unionfs-fuse — A user space Unionfs implementation.

https://github.com/rpodgorny/unionfs-fuse || unionfs-fuse

Read-only file systems

• EROFS — Enhanced Read-Only File System is a lightweight read-only file system, it aims to improve performance and compress storage capacity.

https://www.kernel.org/doc/html/latest/filesystems/erofs.html || erofs-utils

• SquashFS — SquashFS is a compressed read only filesystem. SquashFS compresses files, inodes and directories, and supports block sizes up to 1 MB for greater compression.

https://github.com/plougher/squashfs-tools || squashfs-tools

Clustered file systems

• Ceph — Unified, distributed storage system designed for excellent performance, reliability and scalability.

https://ceph.com/ || ceph

• Glusterfs — Cluster file system capable of scaling to several peta-bytes.

https://www.gluster.org/ || glusterfs

• IPFS — A peer-to-peer hypermedia protocol to make the web faster, safer, and more open. IPFS aims replace HTTP and build a better web for all of us. Uses blocks to store parts of a file, each network node stores only content it is interested, provides deduplication, distribution, scalable system limited only by users. (currently in alpha)

https://ipfs.io/ || go-ipfs

• MooseFS — MooseFS is a fault tolerant, highly available and high performance scale-out network distributed file system.

https://moosefs.com || moosefs

• OpenAFS — Open source implementation of the AFS distributed file system

https://www.openafs.org || openafsAUR

• OrangeFS — OrangeFS is a scale-out network file system designed for transparently accessing multi-server-based disk storage, in parallel. Has optimized MPI-IO support for parallel and distributed applications. Simplifies the use of parallel storage not only for Linux clients, but also for Windows, Hadoop, and WebDAV. POSIX-compatible. Part of Linux kernel since version 4.6.

http://www.orangefs.org/ || not packaged? search in AUR

• Sheepdog — Distributed object storage system for volume and container services and manages the disks and nodes intelligently.

https://sheepdog.github.io/sheepdog/ || sheepdogAUR

• Tahoe-LAFS — Tahoe Least-Authority Filesystem is a free and open, secure, decentralized, fault-tolerant, peer-to-peer distributed data store and distributed file system.

https://tahoe-lafs.org/ || tahoe-lafsAUR

Shared-disk file system

• GFS2 — GFS2 allows all members of a cluster to have direct concurrent access to the same shared block storage

https://pagure.io/gfs2-utils || gfs2-utilsAUR

• OCFS2 — The Oracle Cluster File System (version 2) is a shared disk file system developed by Oracle Corporation and released under the GNU General Public License

https://oss.oracle.com/projects/ocfs2/ || ocfs2-toolsAUR

• VMware VMFS — VMware’s VMFS (Virtual Machine File System) is used by the company’s flagship server virtualization suite, vSphere.

https://www.vmware.com/products/vi/esx/vmfs.html || vmfs-toolsAUR

Identify existing file systems

To identify existing file systems, you can use lsblk:

An existing file system, if present, will be shown in the FSTYPE column. If mounted, it will appear in the MOUNTPOINT column.

Create a file system

File systems are usually created on a partition, inside logical containers such as LVM, RAID and dm-crypt, or on a regular file (see Wikipedia:Loop device). This section describes the partition case.

Before continuing, identify the device where the file system will be created and whether or not it is mounted. For example:

Mounted file systems must be unmounted before proceeding. In the above example an existing filesystem is on /dev/sda2 and is mounted at /mnt . It would be unmounted with:

To find just mounted file systems, see #List mounted file systems.

To create a new file system, use mkfs(8) . See #Types of file systems for the exact type, as well as userspace utilities you may wish to install for a particular file system.

For example, to create a new file system of type ext4 (common for Linux data partitions) on /dev/sda1 , run:

The new file system can now be mounted to a directory of choice.

Mount a file system

To manually mount filesystem located on a device (e.g., a partition) to a directory, use mount(8) . This example mounts /dev/sda1 to /mnt .

This attaches the filesystem on /dev/sda1 at the directory /mnt , making the contents of the filesystem visible. Any data that existed at /mnt before this action is made invisible until the device is unmounted.

fstab contains information on how devices should be automatically mounted if present. See the fstab article for more information on how to modify this behavior.

If a device is specified in /etc/fstab and only the device or mount point is given on the command line, that information will be used in mounting. For example, if /etc/fstab contains a line indicating that /dev/sda1 should be mounted to /mnt , then the following will automatically mount the device to that location:

mount contains several options, many of which depend on the file system specified. The options can be changed, either by:

• using flags on the command line with mount
• editing fstab
• creating udev rules
• compiling the kernel yourself
• or using filesystem-specific mount scripts (located at /usr/bin/mount.* ).

See these related articles and the article of the filesystem of interest for more information.

List mounted file systems

To list all mounted file systems, use findmnt(8) :

findmnt takes a variety of arguments which can filter the output and show additional information. For example, it can take a device or mount point as an argument to show only information on what is specified:

findmnt gathers information from /etc/fstab , /etc/mtab , and /proc/self/mounts .