How Linux Works -- Directory Hierarchy --
Linux Directory Hierarchy Essentials
/binContains ready-to-run programs (also known as an executables), including most of the basic Unix
commands such as ls and cp.
/devContains device files. Explained later probably...
/etcThis core system configuration directory (pronounced EHT-see) contains the user password, boot,
device, networking, and other setup files. Many items in /etc are specific to the machine’s hardware. For
example, the /etc/X11 directory contains graphics card and window system configurations.
/homeHolds personal directories for regular users.
/libAn abbreviation for library, this directory holds library files containing code that executables can use.
There are two types of libraries: static and shared. The /lib directory should contain only shared libraries (cf. /usr/share)
/procProvides system statistics through a browsable directory-and-file interface. The /proc
directory contains information about currently running processes as well as some kernel parameters.
/sysThis directory is similar to /proc in that it provides a device and system interface.
/sbinThe place for system executables. Programs in /sbin directories relate to system management, so
regular users usually do not have /sbin components in their command paths.
/usrAlthough pronounced “user,” this subdirectory has no user files. Instead, it contains a large directory
hierarchy, including the bulk of the Linux system.
/varThe variable subdirectory, where programs record runtime information. System logging, user tracking,
caches, and other files that system programs create and manage are here.
About /usr directory
/usr is where most of the user-space programs and data reside. In addition to
/usr contains the following:
/includeHolds header files used by the C compiler.
/infoContains GNU info manuals
/localIs where administrators can install their own software. Its structure should look like that of / and /usr.
/manContains manual pages.
/shareContains files that should work on other kinds of Unix machines with no loss of functionality.
Contents above are entirely based on How Linux Works, 2nd Edition: What Every Superuser Should Know