Linux Provides a Secure Hierarchical Filesystem

A file is a collection of information, such as text for a memo or report, an accumulation of sales figures, an image, a song, or an executable program. Each file is stored under a unique identifier on a storage device, such as a hard disk. The Linux filesystem provides a structure whereby files are arranged under directories, which are like folders or boxes. Each directory has a name and can hold other files and directories. Directories, in turn, are arranged under other directories, and so forth, in a treelike organization. This structure helps users keep track of large numbers of files by grouping related files in directories. Each user has one primary directory and as many subdirectories as required.

Standards. With the idea of making life easier for system administrators and software developers, a group got together over the Internet and developed the Linux Filesystem Standard (FSSTND), which has since evolved into the Linux Filesystem Hierarchy Standard (FHS). Before this standard was adopted, key programs were located in different places in different Linux distributions. Today you can sit down at a Linux system and know where to expect to find any given standard program.

Links. A link allows a given file to be accessed by means of two or more names. The alternative names can be located in the same directory as the original file or in another directory. Links can make the same file appear in several users’ directories, enabling those users to share the file easily. Windows uses the term shortcut in place of link to describe this capability. Macintosh users will be more familiar with the term alias. Under Linux, an alias is different from a link; it is a command macro feature provided by the shell.

Security. Like most multiuser operating systems, Linux allows users to protect their data from access by other users. It also allows users to share selected data and programs with certain other users by means of a simple but effective protection scheme. This level of security is provided by file access permissions, which limit which users can read from, write to, or execute a file. More recently, Linux has implemented Access Control Lists (ACLs), which give users and administrators finer-grained control over file access permissions.

Source of Information : A Practical Guide to Ubuntu Linux