Linux has several filesystem drivers for the File Allocation Table (FAT) filesystem format. These are commonly known by the names used in the <code>mount</code> command to invoke particular drivers in the kernel: ', ', and '.

History and support

Most of the major Linux distributions, including RedHat, SuSE, and Debian, do not employ ' to permit installation of Linux on a FAT disc volume. A few distributions do, however. These include distributions such as Phat Linux, which installs in <code>C:\PHAT</code> on DOS by unpacking a ZIP file and is booted by running a COMMAND.COM script named <code>LINUX.BAT</code>, UVFAT, an extension of UMSDOS to use the Windows data structures for long filenames instead of its own, was discontinued before release. They should work in 2.4.x kernels.

Earlier Linux distributions which used UMSDOS are MuLinux, Monkey Linux and Winlinux 2000.

Feature comparison

All of the Linux filesystem drivers support all three FAT types, namely FAT12, FAT16 and FAT32. Where they differ is in the provision of support for long filenames, beyond the 8.3 filename structure of the original FAT filesystem format, and in the provision of Unix file semantics that do not exist as standard in the FAT filesystem format such as file permissions.

The ' filesystem driver provides no extra Unix file semantics and no long filename support. If a FAT disk filesystem is mounted using this driver, only 8.3 filenames will be visible, no long filenames will be accessible, nor will any long filename data structures of any kind on the disk volume be maintained. The ' filesystem driver provides long filename support using the same disk data structures that Microsoft Windows uses for VFAT long filename support on FAT format volumes, but it does not support any extra Unix file semantics. The ' filesystem driver provides long filename support, and extra Unix file semantics. However, it does so using on-disk data structures that are not recognized by any filesystem drivers for any operating systems other than Linux.

The key advantage to ' out of the three is that it provides full Unix file semantics. Therefore, it can be used in situations where it is desirable to install Linux on and run it from a FAT disk volume, which require such semantics to be available. However, Linux installed on and running from such a disk volume is slower than Linux installed on and running from a disk volume formatted with, for example, the ext2 filesystem format. Further, unless a utility program is regularly run every time that one switches from running Windows to running Linux, certain changes made to files and directories on the disk by Windows will cause error messages about inaccessible files in Linux.

', although lacking full Unix file semantics and lacking the ability to have Linux installed on and running from a FAT disk volume, does not have the aforementioned disadvantages of ' when it comes to simply sharing data on a FAT disk volume between Linux and other operating systems such as Windows. Its data structures are the same as those used by Windows for VFAT long filenames, and it does not require running a synchronization utility in order to prevent Windows and Linux data structures from becoming disjointed. For this reason, it is the most appropriate of Linux's FAT filesystem drivers to use in the majority of situations.

The installation of Linux into such a directory in the first place simply involves unpacking files from an archive into that directory and its subdirectories. Such an installation also generally requires the use of a swap file rather than a swap partition for Linux, however this is related to the desire not to repartition the hard disc and unrelated to the ' filesystem driver per se.

Alternately, one of the FUSE filesystem drivers may be used—FatFuse, FuseFat or .

POSIX overlay filesystem

A modern equivalent of UMSDOS is POSIX Overlay Filesystem (). It works in FUSE.

See also

  • DMSDOS (DoubleSpace/DriveSpace/Stacker compatible compressed FAT volumes for Linux)
  • Design of the FAT file system

References

Further reading

  • UMSDOS developer’s page
  • New Linux patch could circumvent Microsoft's FAT patents by Ryan Paul