Cramfs

CramFs (Compressed ROMANIAN/RAM System File) is a Filesystem compressed under Linux in reading alone; it was conceived for simplicity and to hold less possible place in random access memory (RAM). It is in particular used for the Onboard computing.

Contrary to a compressed image of a conventional filesystem, there does not need to start by decompressing the file. For this reason, this filesystem is used in the Distributions Linux:

for the Initrd (Initial RamDisk), by Debian
for images of installation (for example, on SuSE)

The type of compression is Zlib (see RFC 1950).

History

CRAMFS is used for initrd by the Noyau Linux since the version of development 2.5.46 of the core. The exact name of this form of initrd is initramfs.

Utilities

cramfsswap

A CramFs filesystem generated for a processor little endian will not function on a computer big endian. To mitigate this problem, the utility cramfsswap makes it possible to rock the generated filesystem from one mode to another.

mkcramfs

mkcramfs formate a Partition of hard drive to the CramFs format.

Technical limitations

the size of the files is limited to less than 16 Mo.
the maximum size of the filesystem is 256 Mo.
the Identifiant of group (GID) is truncated: only the 8 bits of weak weights are preserved. That can present security issues.
the physical bonds are supported, but the meter of bond will be always to 1.
It does not have there a repertory ". " (oneself) or ". " (the father). NB: it is useless to use the option - noleaf order find

Comparative

Example of other filesystems compressed under Linux in reading alone: squashFS, isoFS. The driver cloop (Compressed LOOPback device) of Knoppix makes it possible to decompress the contents of a LiveCD.

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