Squashfs is a compressed read-only

file system In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

for

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

. Squashfs compresses files,

inode The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. File-system object attribute ...

s and

directories Directory may refer to: * Directory (computing), or folder, a file system structure in which to store computer files * Directory (OpenVMS command) * Directory service, a software application for organizing information about a computer network's ...

, and supports block sizes from 4

KiB The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...

up to 1 MiB for greater compression. Several compression algorithms are supported. Squashfs is also the name of

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...

, licensed under the

GPL The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general u ...

, for accessing Squashfs filesystems. Squashfs is intended for general read-only file-system use and in constrained block-device memory systems (e.g.

embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...

s) where low overhead is needed.

Uses

Squashfs is used by the

Live CD A live CD (also live DVD, live disc, or live operating system) is a complete bootable computer installation including operating system which runs directly from a CD-ROM or similar storage device into a computer's memory, rather than loading fro ...

versions of

Arch Linux Arch Linux () is an independently developed, x86-64 general-purpose Linux distribution that strives to provide the latest stable versions of most software by following a Rolling release, rolling-release model. The default installation is a minim ...

Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of D ...

, Fedora,

Gentoo Linux Gentoo Linux (pronounced ) is a Linux distribution built using the Portage package management system. Unlike a binary software distribution, the source code is compiled locally according to the user's preferences and is often optimized for the ...

Linux Mint Linux Mint is a community-driven Linux distribution based on Ubuntu (which is in turn based on Debian), bundled with a variety of free and open-source applications. It can provide full out-of-the-box multimedia support for those who choose to i ...

openSUSE openSUSE () is a free and open-source software, free and open source RPM Package Manager, RPM-based Linux distribution developed by the openSUSE project. The initial release of the community project was a beta version of SUSE Linux 10.0. Addi ...

Salix Willows, also called sallows and osiers, from the genus ''Salix'', comprise around 400 speciesMabberley, D.J. 1997. The Plant Book, Cambridge University Press #2: Cambridge. of typically deciduous trees and shrubs, found primarily on moist s ...

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All ...

NixOS NixOS is a Linux distribution built on top of the Nix package manager. It uses declarative configuration and allows reliable system upgrades. Several official package "channels" are offered, including the current Stable release and the Unstable ...

Clonezilla Clonezilla is a suite of open source drive cloning, drive imaging and system deployment utilities used to simplify deployment and maintenance of a group of computers. Clonezilla Server Edition uses multicast technologies to deploy a single im ...

Kali Linux Kali Linux is a Debian-derived Linux distribution designed for digital forensics and penetration testing. It is maintained and funded by Offensive Security. Kali Linux has around 600 penetration-testing programs (tools), including Armitage (a ...

and on embedded distributions such as the

OpenWrt OpenWrt (from ''open wireless router'') is an open-source project for embedded operating systems based on Linux, primarily used on embedded devices to route network traffic. The main components are Linux, util-linux, musl, and BusyBox. All com ...

and

DD-WRT DD-WRT is Linux-based firmware for wireless routers and access points. Originally designed for the Linksys WRT54G series, it now runs on a wide variety of models. DD-WRT is one of a handful of third-party firmware projects designed to replac ...

router

firmware In computing, firmware is a specific class of computer software that provides the low-level control for a device's specific hardware. Firmware, such as the BIOS of a personal computer, may contain basic functions of a device, and may provide h ...

. It is also used in Chromecast and for the system partitions of some Android releases (

Android Nougat Android Nougat ( codenamed Android N during development) is the seventh major version and 14th original version of the Android operating system. First released as an alpha test version on March 9, 2016, it was officially released on August 22, ...

). It is often combined with a

union mount In computer operating systems, union mounting is a way of combining multiple directories into one that appears to contain their combined contents. Union mounting is supported in Linux, BSD and several of its successors, and Plan 9, with similar ...

filesystem, such as

UnionFS Unionfs is a filesystem service for Linux, FreeBSD and NetBSD which implements a union mount for other file systems. It allows files and directories of separate file systems, known as branches, to be transparently overlaid, forming a single coher ...

OverlayFS In computing, OverlayFS is a union mount filesystem implementation for Linux. It combines multiple different underlying mount points into one, resulting in single directory structure that contains underlying files and sub-directories from all sou ...

, or

aufs aufs (short for advanced multi-layered unification filesystem) implements a union mount for Linux file systems. The name originally stood for AnotherUnionFS until version 2. Developed by Junjiro Okajima in 2006, aufs is a complete rewrite of t ...

, to provide a read-write environment for live Linux distributions. This takes advantage of both Squashfs's high-speed compression abilities and the ability to alter the distribution while running it from a live CD. Distributions such as

Debian Live Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of Deb ...

, Mandriva One,

Puppy Linux Puppy Linux is an operating system and family of light-weight Linux distributions that focus on ease of use and minimal memory footprint. The entire system can be run from random-access memory (RAM) with current versions generally taking up abou ...

, Salix Live and

Slax Slax is a LiveCD Linux distribution developed by Tomáš Matějíček and based on upstream customizable Linux distributions. Packages can be added by apt package manager or can be prepared as modules. The tagline for Slax refers to itself as " ...

use this combination. The

AppImage AppImage is a format for distributing portable software on Linux without needing superuser permissions to install the application. It tries also to allow Linux distribution-agnostic binary software deployment for application developers, als ...

project, which aims to create portable linux applications, uses squashfs for creating appimages. The Snappy package manager also uses squashfs for its ".snap file format". Squashfs is also used by

Linux Terminal Server Project Linux Terminal Server Project (LTSP) is a free and open source terminal server for Linux that allows many people to simultaneously use the same computer. Applications run on the server with a terminal known as a thin client (also known as an X te ...

and

Splashtop Splashtop is a family of remote-desktop software and remote support software, developed by Splashtop Inc. Splashtop enables users to remotely access or remotely support computers from desktop and mobile devices. Splashtop enables remote compu ...

. The tools ''unsquashfs'' and ''mksquashfs'' have been ported to

Windows NT Windows NT is a proprietary graphical operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems sc ...

– Windows 8.1.

7-Zip 7-Zip is a free and open-source file archiver, a utility used to place groups of files within compressed containers known as "archives". It is developed by Igor Pavlov and was first released in 1999. 7-Zip has its own archive format called 7z, ...

also supports Squashfs.

History

Squashfs was initially maintained as an out-of-tree Linux patch. The initial version 1.0 was released on 23 October 2002. In 2009 Squashfs was merged into Linux mainline as part of Linux 2.6.29. In that process, the

backward-compatibility Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially i ...

code for older formats was removed. Since then the Squashfs

kernel-space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

code has been maintained in the Linux mainline tree, while the

user-space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

tools remain on the project's

GitHub GitHub, Inc. () is an Internet hosting service for software development and version control using Git. It provides the distributed version control of Git plus access control, bug tracking, software feature requests, task management, continuous ...

page. The original version of Squashfs used

gzip gzip is a file format and a software application used for file compression and decompression. The program was created by Jean-loup Gailly and Mark Adler as a free software replacement for the compress program used in early Unix systems, and i ...

compression, although Linux kernel 2.6.34 added support for LZMA and LZO compression, Linux kernel 2.6.38 added support for LZMA2 compression (which is used by xz), Linux kernel 3.19 added support for LZ4 compression, and Linux kernel 4.14 added support for

Zstandard Zstandard, commonly known by the name of its reference implementation zstd, is a lossless data compression algorithm developed by Yann Collet at Facebook. ''Zstd'' is the reference implementation in C. Version 1 of this implementation was r ...

compression. Linux kernel 2.6.35 added support for

extended file attributes Extended file attributes are file system features that enable users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as permissions or re ...

References

External links

* {{File systems Compression file systems Free special-purpose file systems Read-only file systems supported by the Linux kernel Free software programmed in C

Uses

History

See also

References

External links