SQUASHFS

Squashfs 3.2-r2 released (15th January 2007). Please see CHANGES and README files in new file release.

Squashfs is a compressed read-only filesystem for Linux. Squashfs is intended for general read-only filesystem use, for archival use (i.e. in cases where a .tar.gz file may be used), and in constrained block device/memory systems (e.g. embedded systems) where low overhead is needed. The filesystem is currently stable, and has been tested on PowerPC, i586, Sparc and ARM architectures.

If you're looking for LZMA support please go to the bottom of this page.

You can go to the download page or the summary page. On the summary page there are links to the public forums, and the mailing lists. Queries, problems, etc. please send a message to the public forums, the mailing lists or email me (email at bottom of page). You can also go to the Squashfs HOWTO, written by Artemiy I. Pavlov.

I'm always interested to hear how people are using Squashfs, whether you're using it for archiving, as the filesystem in an embedded device, or for anything else, unexpected or otherwise. Hopefully, I'll be able to build up a list, which will be useful when I try to get it added to the kernel.

Squashfs overview

Data, inodes and directories are compressed.
Squashfs stores full uid/gids (32 bits), and file creation time.
Files up to 2^64 bytes are supported. Filesystems can be up to 2^64 bytes.
Inode and directory data are highly compacted, and packed on byte boundaries. Each compressed inode is on average 8 bytes in length (the exact length varies on file type, i.e. regular file, directory, symbolic link, and block/char device inodes have different sizes).
Squashfs can use block sizes up to 64K (the default size is 64K). Using 64K blocks achieves greater compression ratios than the normal 4K block size.
File duplicates are detected and removed.
Both big and little endian architectures are supported. The mksquashfs program can generate filesystems for different endian architectures for cases where the host byte ordering is different to the target. This is useful for embedded systems.

Installing squashfs

The squashfs file release contains a README, the squashfs patch files, and the squashfs-tools directory (mksquashfs). Please see the INSTALL file for install instructions.

Using squashfs

The README file contains details on using squashfs, and contains brief filesystem design notes...

GZIP and LZMA support for Squashfs

The official releases of Squashfs supports GZIP compression because this is the only compression supported by the Linux kernel. If you want LZMA support then please visit www.squashfs-lzma.org. These are high quality patches provided by Tomas Matejicek (SLAX) and Junjiro Okajima. At the time of writing, the patches are against Squashfs 3.2, they should be updated to the latest release in the near future.

Contact

The author can be contacted by email, phillip at lougher.demon.co.uk or plougher at users.sourceforge.net.