The UNIX and LINUX operating system is further divided into:

• The Kernel
• The Shell
• The Directory Hierarchy

Kernel: The Kernel is the core of the UNIX and LINUX operating system. Kernel’s role is to manage all the physical resources of the computer in the best possible way.

• File System and Structure
• Device management for storing data.
• Process management or CPU functions
• Memory management

The Shell: Shell is the interface between the Kernel and the user. Shell interprets the command to the Kernel and shows the response to the user. Kernel reacts when it gets the command from Shell.

Three default Shell available:

Bash Shell: also known as Bourne Shell. This is the default shell for the root users. Root user is a special user with unlimited access privileges for the System Administrator. The default Bourne shell prompt for regular user is $ and for root user is #.

C Shell: has many features the Bourne shell does not like command-line history, aliasing, and job control. The default C shell prompt for a regular user is the host name followed by a percent sign (hostname%); for the root user the default shell prompt is the host name followed by a pound sign (hostname#).

Korn Shell: this shell is the superset of Bourne shell and has more additional features than Bourne and C shell. The regular user prompt is $ and for root user is #.

Alternative Shells

TC shell: TC shell is compatible with C programming language. It is used by C programmers.

Z shell: It is similar to the Korn shell but included more additional features.

SA shell: this is a Stand alone shell. It has the minimal shell features that runs in most of the environment. It is used for system troubleshooting.

The Directory Hierarchy: in UNIX and LINUX environment, the file system is in the form of directory listing.

In UNIX and LINUX:

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