Linux Directory Hierarchy Essentials

• /bin Contains ready-to-run programs (also known as an executables), including most of the basic Unix commands such as ls and cp.
• /dev Contains device files. Explained later probably...
• /etc This 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.
• /home Holds personal directories for regular users.
• /lib An 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)
• /proc Provides system statistics through a browsable directory-and-file interface. The /proc directory contains information about currently running processes as well as some kernel parameters.
• /sys This directory is similar to /proc in that it provides a device and system interface.
• /sbin The 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.
• /tmp skip
• /usr Although pronounced “user,” this subdirectory has no user files. Instead, it contains a large directory hierarchy, including the bulk of the Linux system.
• /var The 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/bin, /usr/sbin, and /usr/lib, /usr contains the following:

• /include Holds header files used by the C compiler.
• /info Contains GNU info manuals
• /local Is where administrators can install their own software. Its structure should look like that of / and /usr.
• /man Contains manual pages.
• /share Contains 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