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 lar ...

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 i ...

. Squashfs compresses

files File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

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 attribu ...

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 up to 1

MiB 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 ...

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, ...

, licensed under the GPL, for accessing Squashfs filesystems. Squashfs is intended for general read-only file-system use and in constrained block-device

memory system A mnemonic ( ) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding. Mnemonics make use of elaborative encoding, retrieval cues, and imager ...

s (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'' ...

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 f ...

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 model. The default installation is a minimal base system, ...

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 De ...

Fedora A fedora () is a hat with a soft brim and indented crown.Kilgour, Ruth Edwards (1958). ''A Pageant of Hats Ancient and Modern''. R. M. McBride Company. It is typically creased lengthwise down the crown and "pinched" near the front on both sides ...

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 t ...

, Linux Mint, openSUSE,

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, NixOS, Clonezilla, Kali Linux 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. A ...

and DD-WRT 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 ...

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

Android Android may refer to: Science and technology * Android (robot), a humanoid robot or synthetic organism designed to imitate a human * Android (operating system), Google's mobile operating system ** Bugdroid, a Google mascot sometimes referred to ...

releases ( Android Nougat). It is often combined with a union mount filesystem, such as UnionFS, OverlayFS, or aufs, 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, Mandriva One, Puppy Linux, Salix Live and Slax use this combination. The AppImage 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 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 comput ...

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

Windows NT Windows NT is a proprietary graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-user operating system. The first version of Wi ...

– Windows 8.1. 7-Zip 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 code for older formats was removed. Since then the Squashfs kernel-space 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. Kern ...

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, co ...

page. The original version of Squashfs used gzip 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 compression. Linux kernel 2.6.35 added support for extended file attributes.

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