The file system structure is the most basic level of
organization in an operating system. Almost all of the ways an
operating system interacts with its users, applications, and
security model are dependent upon the way it organizes files on
storage devices. Providing a common file system structure ensures
users and programs are able to access and write files.
File systems break files down into two logical categories:
Shareable files are those that can be
accessed locally and by remote hosts; unsharable files are only available locally.
Variable files, such as documents, can be
changed at any time; static files, such as
binaries, do not change without an action from the system
administrator.
The reason for looking at files in this manner is to help
correlate the function of the file with the permissions assigned to
the directories which hold them. The way in which the operating
system and its users interact with a given file determines the
directory in which it is placed, whether that directory is mounted
with read-only or read/write permissions, and the level of access
each user has to that file. The top level of this organization is
crucial. Access to the underlying directories can be restricted or
security problems could manifest themselves if, from the top level
down, it does not adhere to a rigid structure.
