What is a shell well a shell is software that provides an interface for users of an operating system which provides access to the services of a kernel. The command processor is the program that executes operating system commands. The shell, therefore, is the part of the command processor that accepts commands. After verifying that the commands are valid, the shell sends them to another part of the command processor to be executed. The shell is a program that takes your commands from the keyboard and gives them to the operating system to perform. In the old days, it was the only user interface available on a UNIX computer. Nowadays, we have graphical user interfaces (GUIs) in addition to command line interfaces (CLIs) such as the shell.

On most Linux systems a program called bash (which stands for Bourne Again Shell, an enhanced version of the original Bourne shell program, sh, written by Steve Bourne) acts as the shell program. Besides bash there are several additional shell programs available on a Linux system which includes sh, ksh, csh and tcsh. The differences between bash and the other shells is that bash has a command history features that allows you to recall, edit and rerun previous commands, and command completion when pressing the tab key. Whereas the ksh shell has a scripting features that is not included in bash shell.

Before you install linux you must have a plan on how you want your disk partition. The advantages of planning are you can isolate parts of the file system, so that they can be preserved if you reinstall the operating system. Separate data that changes frequently from data that change infrequently, which can reduce disk fragmentation and prolong the life of the system. Separating data that you want backed up into a separate partition can make your back up procedures much simpler. Make your system more resilient to attack, if your system becomes the target of an attack or one of your programs behaves badly, it can create large log files or other files which can fill up the whole disk, however if you have multiple partitions, it can only ever fill up one partition which means your system is less likely to crash.
The primary partition is one that is used to store the operating system. Primary partitions can hold operating system boot files, cannot be further subdivided into logical drives, and can be formatted. There can be a maximum of four primary partitions on a single hard disk drive. Extended partition is an optional partition that does not have an operating system installed on it and is not bootable. Extended partition can be subdivided into an unlimited number of logical drives, and cannot be formatted. There can be a maximum of one extended partition on a single hard disk drive. Using the fdisk utility will help you created these partitions on a hard disk.