Editing FAT filesystem and Linux (section)

=== {{anchor|--LINUX-.---}}{{anchor|Data structures of umsdos}} Data structure ===
The ''{{Not a typo|umsdos}}'' FAT filesystem driver stores all of the extra information relating to Unix file semantics in what, to another FAT filesystem driver, appears to be just a normal file in each directory and subdirectory, named <code>--LINUX-.---</code>.<ref name="StanfieldSmith"/><ref name="Smith1"/><ref name="McCune"/><ref name="Smith2"/><ref name="Danesh"/>

In the absence of this file in any given directory, and thus by default, the ''{{Not a typo|umsdos}}'' filesystem driver provides the same semantics as the ''{{Not a typo|msdos}}'' filesystem driver does for the directory: only 8.3 filenames and no extra Unix file semantics.  To enable the ''{{Not a typo|umsdos}}'' driver's extra abilities, it is necessary to create that file in the directory and synchronize its internal data with the normal FAT data for any existing entries already in the directory.   This is done with a tool called <code>umssync</code>.<ref name="StanfieldSmith"/><ref name="Smith1"/><ref name="McCune"/>

This is the utility program that is run, across every directory on the disc volume, every time that one switches from running Windows to running Linux, in order for the ''{{Not a typo|umsdos}}'' filesystem driver to incorporate any changes made to files and directories by Windows into its private data structures in its <code>--LINUX-.---</code> file.  By default, the <code>umssync</code> tool creates <code>--LINUX-.---</code> files in directories if they do not already exist, resulting in such a file in every directory in the disc volume.  When switching between Windows and Linux this behaviour is not often considered desirable.  Therefore, the normal mode of operation when invoking <code>umssync</code> after switching from Windows to Linux (which is usually done by running the tool at Linux boot time from a startup script) is to employ the <code>-c</code> option to the command, which prevents the creation of any new <code>--LINUX-.---</code> files in directories that do not already possess them.<ref name="StanfieldSmith"/><ref name="Smith1"/><ref name="McCune"/>