This standard assumes that the operating system underlying an FHS-compliant file system supports the same basic security features found in most UNIX filesystems
It is possible to define two independent distinctions among files: shareable vs. unshakable and variable vs. static. In general, files that differ in either of these respects should be located in different directories. This makes it easy to store files with dirfferent usage characteristics on different filesystem.
"Shareable" files are those that can be stored on one host and used on others. "Unshakable" files are those that are not shareable. For example, the files in user home directories are shareable whereas device lock file are not.
"Static" files include binaries, libraries, documentation files and other files that do not change without system administrator intervention.
"Variable" files are files that are not static.