| Developer | Phillip Lougher, Robert Lougher |
|---|---|
| Introduced | 2009 (Linux 2.6.29) |
| Limits | |
| Max file size | 16 EiB |
| Max volume size | 16 EiB |
| Features | |
| Transparent compression | gzip LZMA LZO xz |
| Supported operating systems | Linux |
SquashFS (.sfs) is a compressed read-only file system for Linux. SquashFS compresses files, inodes and directories, and supports block sizes up to 1 MB for greater compression. SquashFS is also the name of free/open software, licensed under the GPL, for accessing SquashFS filesystems.
SquashFS is intended for general read-only file system use and in constrained block device/memory systems (e.g. embedded systems) where low overhead is needed. The original version of SquashFS used gzip compression, although Linux kernel 2.6.34 added support for LZMA[1] and LZO compression[2], and Linux kernel 2.6.38 added support for xz compression.[3]
Linux kernel 2.6.35 added support for Extended file attributes.[4]
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SquashFS is used by the Live CD versions of Arch Linux, Debian, Fedora, Gentoo Linux, Salix, Ubuntu and on embedded distributions such as the OpenWrt[5] and DD-WRT router firmware. It is often combined with a union mount filesystem, such as UnionFS or aufs, to provide a read-write environment for live Linux distributions. This takes advantage of both the 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 on-disk format of SquashFS has stabilized enough that it has been merged into the 2.6.29 version of the Linux kernel.[6] In that process, the backward-compatibility code for older formats was removed.[7]
SquashFS is also used by Linux Terminal Server Project, Slax, and Splashtop. The SquashFS files might use extension .sqx also used for SQX. The tools unsquashfs and mksquashfs have been ported to Windows NT,[8] read access is also possible with 7-zip.