Cramfs
844158
201566870
2008-03-28T13:11:10Z
82.119.242.94
cramfs on sourceforge is obsolete, linked to util-linux instead
The '''compressed ROM file system''' (or '''cramfs''') is a [[Free software|free]] ([[GNU General Public License|GPL]]'ed) read-only [[Linux kernel|Linux]] [[file system]] designed for simplicity and space-efficiency. It is mainly used in [[embedded system]]s and small-footprint systems.
Unlike a compressed image of a conventional file system, a cramfs image can be used as it is i.e. without the need to decompress the image first. For this reason, some [[Linux distribution]]s also use cramfs for [[initrd]] images ([[Debian]] 3.1 in particular) and installation images ([[SUSE Linux]] in particular), where there are constraints on memory and image size.
== Design ==
Files on cramfs file systems are [[zlib]]-compressed one page at a time to allow random read access. The meta-data is not compressed, but is expressed in a terse representation that is designed to be more space-efficient than conventional file systems.
The file system is intentionally read-only to simplify its design; random write access for compressed files is difficult to implement. cramfs ships with a utility (<code>mkcramfs</code>) to pack files into new cramfs images.
File sizes are limited to less than 16MB.
Maximum file system size is a little over 256MB. (The last file on the file system must begin before the 256MB block, but can extend past it.)
== See also ==
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* [[List of file systems]]
* [[Comparison of file systems]]
* [[SquashFS]], a read-only compressed file system
* [[Util-linux]] contains the cramfs utilities
[[Category:Free special purpose file systems]]
[[Category:Compression file systems]]
[[Category:Linux file systems]]
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