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RHCE tutorial : Part 1 - Introduction

In 1969, a team of developers in the Bell Labs laboratories started working on a solution for the software problem, to address these compatibility issues. They developed a new operating system, which was

  1. Simple and elegant.
  2. Written in the C programming language instead of in assembly code.
  3. Able to recycle code.
The Bell Labs developers named their project "UNIX."

Linux is a UNIX-base operating system. Its original creator was a Finnish student name Linus Torvalds, although being ‘open source’ it has change a great deal since its original conception. It belongs to nobody, and is free to download and use. Any changes to it are open for all to adopt, and as a result it has developed into a very powerful OS that is rapidly gaining in popularity worldwide

Because it is Open Source,  we got different flavours of Linux.

The UNIX operating system is made up of three parts; the kernel, the shell and the programs.

The kernel

The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls.
As an illustration of the way that the shell and the kernel work together, suppose a user types rm myfile (which has the effect of removing the file myfile). The shell searches the filestore for the file containing the program rm, and then requests the kernel, through system calls, to execute the program rm on myfile. When the process rm myfile has finished running, the shell then returns the UNIX prompt % to the user, indicating that it is waiting for further commands.

vmlinuz is the kernel in Redhat Linux operating system.

The shell

The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
The adept user can customise his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.
The tcsh shell has certain features to help the user inputting commands.
Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.
History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.

Examples: bash shell,
C-shell, (csh)
Basic Shell (sh)

Bash and chs are multiuser and sh is single user shell.

What is the difference between a shell and a kernel?

Basically the kernel is the center of the operating system that manages everything. The shell is just a particular program, a friendly interface that translates your commands into some low-level calls to the kernel

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