http://www.ruanyifeng.com/blog/2012/02/a_history_of_unix_directory_structure.html
http://www.pathname.com/fhs/pub/fhs-2.3.html
http://lists.busybox.net/pipermail/busybox/2010-December/074114.html
/home : User home directories (optional)
Purpose
/home is a fairly standard concept, but it is clearly a site-specific filesystem. [9] The setup will differ from host to host. Therefore, no program should rely on this location. [10]
/root : Home directory for the root user (optional)
Purpose
The root account’s home directory may be determined by developer or local preference, but this is the recommended default location. [17]
/opt : Add-on application software packages
Purpose
/opt is reserved for the installation of add-on application software packages.
A package to be installed in /opt must locate its static files in a separate /opt/<package> or /opt/<provider> directory tree, where <package> is a name that describes the software package and <provider> is the provider’s LANANA registered name.
/etc : Host-specific system configuration
Purpose
The /etc hierarchy contains configuration files. A “configuration file” is a local file used to control the operation of a program; it must be static and cannot be an executable binary. [4]
