Structure of Linux OS

In Linux the file system is based on one root directory, or hierarchical top point with subdirectories below it. In which each sub-directories has its own importance like some act as mount points, some for log messages, some for all hardware devices etc.

You can find a brief description of all the directories and sub directories below:

/: Its the top most directory in any of the Unix based system.
/bin: Essential command binaries that need to be available in single user mode; for all users, e.g., cat, ls, cp.
/boot: Boot loader files, e.g., kernels, initrd etc.
/dev: Information of all the hardware devices.
/etc: All the config files.
/home: Home directories of all the users in a particular machine.
/media: Mount points for removable media such as USB, CD etc.
/mnt: For temporary mount points.
/opt: Optional software packages like openoffice etc.
/root: Home directory of root user.
/sbin: System binaries like init, ip etc.
/tmp: Temporary files. Often not preserved between system reboots.
/var: Variable files—files whose content is expected to continually change during normal operation of the system—such as logs, spool files, and temporary e-mail files.
/usr: Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.
/lib: Libraries essential for the binaries in /bin and /sbin.