Understanding unix file system

A conceptual understanding of file system, especially data structure and related terms will help you become a successful system administrator. I have seen many new Linux system administrator w/o any clue about file system. The conceptual knowledge can be applied to restore file system in an emergency situation.

What is a File?File are collection of data items stored on disk. Or it's device which can store the information, data, music (mp3), picture, movie, sound, book etc. In fact what ever you store in computer it must be inform of file. Files are always associated with devices like hard disk ,floppy disk etc. File is the last object in your file system tree.

What is a directory?
Directory is group of files. Directory is divided into two types:

Root directory - Strictly speaking, there is only one root directory in your system, which is denoted by / (forward slash). It is root of your entire file system and can not be renamed or deleted.
Sub directory - Directory under root (/) directory is subdirectory which can be created, renamed by the user.
Directories are used to organize your data files, programs more efficiently.

What is a UNIX File system?
A UNIX file system is a collection of files and directories stored. Each file system is stored in a separate whole disk partition. The following are a few of the file system:

/ - Special file system that incorporates the files under several directories including /dev, /sbin, /tmp etc
/usr - Stores application programs
/var - Stores log files, mails and other data
/tmp - Stores temporary files
See The importance of Linux partitions for more information.

But what is in a File system?
Again file system divided into two categories:

User data - stores actual data contained in files
Metadata - stores file system structural information such as superblock, inodes, directories