CramFS

from Wikipedia, the free encyclopedia

The cramfs ( Compressed ROM File System , alternatively: " cram a f ile s ystem Onto a small ROM" ) is a free and under the GPL standing Read-only file system with integrated data compression under Linux . It is mainly used in embedded systems , which is why a main focus was placed on the simplicity and the efficiency of the required storage space.

In contrast to a compressed conventional file system, a CramFS does not first have to be unpacked, but can be accessed directly. For this reason, some Linux distributions use CramFS as the file system for initial Ramdisks ( Debian ) or as installation images ( SuSE up to openSUSE 10.2), as these are subject to some restrictions with regard to their size. Also in embedded systems such as Wi-Fi - routers cramfs is used.

technology

Files in CramFS are compressed with the zlib . The meta information of these files is uncompressed, but is represented in a more concise structure than in conventional file systems. Since write access to a compressed file system is not easy to implement, CramFS can only be accessed for reading.

Machining

To create a CramFS file system and to include files in it, tools such as are mkcramfssupplied as standard . For editing under Linux, the content must be copied into a directory. A new image can then be created from the directory. Windows have tools for direct editing. One of them is newtuxflashtools.zip.

Technical characteristics

CramFS has some limitations such as:

  • File sizes are at 16  Mebibyte limited
  • The maximum size of a file system is a little over 256 Mebibytes. The last file on the file system must begin before the end of the 256 MiB block, but it can extend beyond that.

Alternatives

SquashFS is a compressed file system published in 2002, which compared to CramFS offers, among other things, more effective compression and can handle larger files, but requires more memory .

Web links