# Introduction

This is wimlib version 1.14.4 (February 2024). wimlib is a C library for

creating, modifying, extracting, and mounting files in the Windows Imaging

Format (WIM files). wimlib and its command-line frontend `wimlib-imagex`

provide a free and cross-platform alternative to Microsoft's WIMGAPI, ImageX,

and DISM.

For the release notes, see the [NEWS file](NEWS.md).

# Table of Contents

- [Installation](#installation)

- [Windows](#windows)

- [UNIX-like systems](#unix-like-systems)

- [Installing distro package](#installing-distro-package)

- [Building from source](#building-from-source)

- [WIM files](#wim-files)

- [ImageX implementation](#imagex-implementation)

- [Compression](#compression)

- [NTFS support](#ntfs-support)

- [Windows PE](#windows-pe)

- [Portability](#portability)

- [References](#references)

- [History](#history)

- [Notices](#notices)

# Installation

## Windows

To install wimlib and `wimlib-imagex` on Windows, just download and extract the

ZIP file containing the latest binaries. All official releases are available

from [wimlib.net](https://wimlib.net).

For more details, including directions for how to build from source on Windows

if desired, see [README.WINDOWS.md](README.WINDOWS.md).

## UNIX-like systems

### Installing distro package

To install wimlib and `wimlib-imagex` on UNIX-like systems, first consider just

installing the package provided by your operating system, if there is one.

For example, on Ubuntu and other Debian based systems, run:

sudo apt install wimtools

On Fedora and other Red Hat based systems, run:

sudo dnf install wimlib-utils

On Arch Linux, run:

sudo pacman -S wimlib

### Building from source

To build from source instead, first install the development files for libfuse3

and libntfs-3g, if they're available for your operating system. For example, on

Ubuntu, run:

sudo apt install libfuse3-dev ntfs-3g-dev

Then, if you're building from the git repository instead of from a release

tarball, install additional build dependencies and run the bootstrap script:

sudo apt install autoconf automake libtool pkgconf

./bootstrap

Finally, configure, build, and install the software:

./configure

make

sudo make install

In addition to the standard options, the configure script accepts the following

options:

- `--without-fuse`: Disables support for mounting WIM images. The `wimmount`,

`wimmountrw`, and `wimunmount` commands won't work. This removes the

dependency on libfuse3.

- `--without-ntfs-3g`: Disables support for capturing or applying WIM images

directly from/to NTFS volumes. This removes the dependency on libntfs-3g.

The `mkwinpeimg` shell script also has some optional dependencies that you can

choose to install:

- `cdrkit` (for making ISO filesystems)

- `mtools` (for making disk images)

- `syslinux` (for making disk images)

- `cabextract` (for extracting files from the Windows Automated Installation Kit)

Mounting WIM images also requires the FUSE kernel module. When you try to mount

a WIM image, the FUSE kernel module should be automatically loaded. Mounting

WIM images is only supported on Linux.

# WIM files

A Windows Imaging (WIM) file is an archive designed primarily for archiving

Windows filesystems. However, it can be used on other platforms as well, with

some limitations. Like some other archive formats such as ZIP, files in WIM

archives may be compressed. WIM archives support multiple compression formats,

including LZX, XPRESS, and LZMS. All these formats are supported by wimlib.

A WIM archive contains one or more "images", each of which is a logically

independent directory tree. Each image has a 1-based index and usually a name.

WIM archives provide data deduplication at the level of full file contents. In

other words, each unique "file contents" is only stored once in the archive,

regardless of how many files have that contents across all images.

A WIM archive may be either stand-alone or split into multiple parts.

An update of the WIM format --- first added by Microsoft for Windows 8 ---

supports solid-mode compression. This refers to files being compressed together

(e.g. as in a .tar.xz or .7z archive) rather than separately (e.g. as in a .zip

archive). This usually produces a much better compression ratio. Solid

archives are sometimes called "ESD files" by Microsoft and may have the ".esd"

file extension rather than ".wim". They are supported in wimlib since v1.6.0.

# ImageX implementation

wimlib itself is a C library, and it provides a [documented public

API](https://wimlib.net/apidoc) for other programs to use. However, it is also

distributed with a command-line program called `wimlib-imagex` that uses this

library to implement an imaging tool similar to Microsoft's `ImageX`.

`wimlib-imagex` supports almost all the capabilities of Microsoft's `ImageX` as

well as additional capabilities. `wimlib-imagex` works on both UNIX-like

systems and Windows, although some features differ between the platforms.

Run `wimlib-imagex` with no arguments to see an overview of the available

commands and their syntax. Note that the commands have both long and short

forms, e.g. `wimlib-imagex apply` is equivalent to `wimapply`. For additional

documentation:

- If you have installed `wimlib-imagex` on a UNIX-like system, you will find

further documentation in the man pages; run `man wimlib-imagex` to get

started.

- If you have downloaded the Windows binary distribution, you will find the

documentation for `wimlib-imagex` in PDF format in the `doc` directory. Note

that although the documentation is written in the style of UNIX manual pages,

it does document Windows-specific behavior when relevant.

# Compression

wimlib (and `wimlib-imagex`) can create XPRESS, LZX, and LZMS compressed WIM

archives. wimlib's compression codecs usually outperform and outcompress their

closed-source Microsoft equivalents. Multiple compression levels and chunk

sizes as well as solid mode compression are supported. Compression is

multithreaded by default. Detailed benchmark results and descriptions of the

algorithms used can be found at

[wimlib.net](https://wimlib.net/compression.html).

# NTFS support

WIM images may contain data, such as named data streams and

compression/encryption flags, that are best represented on the NTFS filesystem

used on Windows. Also, WIM images may contain security descriptors which are

specific to Windows and cannot be represented on other operating systems.

wimlib handles this NTFS-specific or Windows-specific data in a

platform-dependent way:

- In the Windows version of wimlib and `wimlib-imagex`, NTFS-specific and

Windows-specific data are supported natively.

- In the UNIX version of wimlib and `wimlib-imagex`, NTFS-specific and

Windows-specific data are ordinarily ignored; however, there is also special

support for capturing and extracting images directly to/from unmounted NTFS

volumes. This was made possible with the help of libntfs-3g from the NTFS-3G

project.

For both platforms the code for NTFS capture and extraction is complete enough

that it is possible to apply an image from the `install.wim` contained in recent

Windows installation media (Vista or later) directly to an NTFS filesystem, and

then boot Windows from it after preparing the Boot Configuration Data. In

addition, a Windows installation can be captured (or backed up) into a WIM file,

and then re-applied later.

# Windows PE

wimlib can also be used to create customized images of Windows PE on either

UNIX-like systems or Windows. Windows PE (Preinstallation Environment) is a

lightweight version of Windows that runs entirely from memory and can be used to

perform maintenance or to install Windows. It is the operating system that runs

when you boot from the Windows installation media.

A copy of Windows PE can be found on the installation media for Windows (Vista

or later) as the file `sources/boot.wim`, or in the Windows Automated

Installation Kit (WAIK), which is free to download from Microsoft.

A shell script `mkwinpeimg` is provided with wimlib on UNIX-like systems to

simplify the process of creating and customizing a bootable Windows PE image,

sourcing the needed files from the Windows installation media or from the WAIK.

# Portability

wimlib works on both UNIX-like systems (Linux, Mac OS X, FreeBSD, etc.) and

Windows (Vista and later).

As much code as possible is shared among all supported platforms, but there

necessarily are some differences in what features are supported on each platform

and how they are implemented. Most notable is that file tree scanning and

extraction are implemented separately for Windows, UNIX, and UNIX (NTFS-3G

mode), to ensure a fast and feature-rich implementation of each platform/mode.

wimlib is mainly used on x86 and x86\_64 CPUs, but it should also work on a

number of other GCC-supported 32-bit or 64-bit architectures. It has been

tested on the ARM and MIPS architectures.

Currently, gcc and clang are the only supported compilers. A few nonstandard

extensions are used in the code.

# References

The WIM file format is partially specified in a document that can be found in

the Microsoft Download Center. However, this document really only provides an

overview of the format and is not a formal specification. It also does not

cover later extensions of the format, such as solid resources.

With regards to the supported compression formats:

- Microsoft has official documentation for XPRESS that is of reasonable quality.

- Microsoft has official documentation for LZX, but in two different documents,

neither of which is completely applicable to its use in the WIM format, and

the first of which contains multiple errors.

- There does not seem to be any official documentation for LZMS, so my comments

and code in `src/lzms_decompress.c` may in fact be the best documentation

available for this particular compression format.

The algorithms used by wimlib's compression and decompression codecs are

inspired by a variety of sources, including open source projects and computer

science papers.

The code in `ntfs-3g_apply.c` and `ntfs-3g_capture.c` uses the [NTFS-3G

library](https://github.com/tuxera/ntfs-3g), which is a library for reading and

writing to NTFS filesystems (the filesystem used by recent versions of Windows).

A limited number of other free programs can handle some parts of the WIM

file format:

- 7-Zip is able to extract and create WIMs (as well as files in many other

archive formats). However, wimlib is designed specifically to handle WIM

files and provides features previously only available in Microsoft's

implementation, such as the ability to mount WIMs read-write as well as

read-only, the ability to create compressed WIMs, the correct handling of

security descriptors and hard links, and support for LZMS compression.

- [`ImagePyX`](https://github.com/maxpat78/ImagePyX) is a Python program that

provides some capabilities of `wimlib-imagex`, with the help of external

compression codecs.

If you are looking for an archive format that provides features similar to WIM

but was designed primarily for UNIX, you may want to consider

[SquashFS](https://docs.kernel.org/filesystems/squashfs.html). However, you may

find that wimlib works surprisingly well on UNIX. It will store hard links and

symbolic links, and it supports storing standard UNIX file permissions (owners,

groups, and modes); special files such as device nodes and FIFOs; and extended

attributes. Actually, I use it to back up my own files on Linux!

# History

wimlib was originally a project started by Carl Thijssen for use on Linux in the

[Ultimate Deployment Appliance](https://www.ultimatedeployment.org). Since then

the code has been entirely rewritten and improved (main author: Eric Biggers).

Windows support has been available since version 1.3.0 (March 2013). A list of

version-to-version changes can be found in the [NEWS file](NEWS.md).

# Notices

wimlib is free software that comes with NO WARRANTY, to the extent permitted by

law. For full details, see the [COPYING file](COPYING).

Bug reports, suggestions, and other contributions are appreciated and should be

posted to [the forums](https://wimlib.net/forums/).

wimlib is independently developed and does not contain any code, data, or files

copyrighted by Microsoft. It is not known to be affected by any patents.