UNIX Filesystems: Evolution, Design, and Implementation

The Filesystem Hierarchy

There are many different types of files in a complete UNIX operating system. These files, together with user home directories, are stored in a hierarchical tree structure that allows files of similar types to be grouped together. Although the UNIX directory hierarchy has changed over the years, the structure today still largely reflects the filesystem hierarchy developed for early System V and BSD variants.

For both root and normal UNIX users, the PATH shell variable is set up during login to ensure that the appropriate paths are accessible from which to run commands. Because some directories contain commands that are used for administrative purposes, the path for root is typically different from that of normal users. For example, on Linux the path for a root and non root user may be:

# echo $PATH
/usr/sbin:/sbin:/bin:/usr/bin:/usr/local/bin:/usr/bin/X11:/root/bin
$ echo $PATH
/home/spate/bin:/usr/bin:/bin:/usr/bin/X11:/usr/local/bin:/home/spate/office52/program

The following list shows the main UNIX directories and the type of files that reside in each directory. Note that this structure is not strictly followed among the different UNIX variants but there is a great deal of commonality among all of them.

/usr. This is the main location of binaries for both user and administrative purposes.

/usr/bin. This directory contains user binaries.

/usr/sbin. Binaries that are required for system administration purposes are stored here. This directory is not typically ...