Linux Introduction (CENTOS/RHEL5)

LINUX INTRODUCTION:

Linux is a high performance, yet completely free, Unix-like operating system that is suitable for use on a wide range of computers and other products. Most distributions (i.e., versions) consist of a kernel (i.e., the core of the operating system) together with hundreds of free utilities and application programs in a coordinated package.

A narrower, and somewhat less common, meaning of the term Linux is just the kernel itself. However, when referring to just the kernel, usually the expression the Linux kernel is used.

Nowadays Linux Operating System is spreading all over the world, not only as a Server Platform but also as a Desktop Platform. In many developed country most of the people are using Linux, as it is illegal to use Windows O/s without License.

SMALL HISTORY:

Linux was started as a hobby in 1991 by Linus Torvalds while a student at the University of Helsinki (in Finland) because he was unhappy with the MS-DOS operating system that came with his new personal computer (with Intel 80386 CPU). He greatly preferred the much more powerful and stable UNIX that he had been using on the university's computers, but he was not able to afford the high licensing fees for any of the commercial versions then available. So he put together kernel to allow some OS components to communicate with computer hardware. By 1995 several companies assembled Linux Kernel with the GNU software of the FSF to produce the first Linux distributions. Today, Torvalds remains the spiritual leader of the Linux movement, and he still coordinates the development of the Linux kernel.

Linux Distribution: (more than 250 distributions)

Virtual Consoles:

When you boot a Linux system without a desktop you see a black screen with a Login: prompt. This is commonly referred to as a Virtual Console (or Virtual Terminalor or Linux Console or Linux Terminal). At this point, you can log in with any user ID available in you system, and the Linux command line prompt appears. At this prompt, you can run Linux commands.

As Linux is a multi terminal (by default 7) operating system, you can log into Linux, even with the same user ID, several times. You can switch between adjacent virtual consoles by pressing ALT + RIGHT ARROW or ALT + LEFT ARROW. For example, to move from virtual console 2 to virtual console 3, press ALT + RIGHT ARROW.

CLI (Command Linux Interface): by default 6 terminals (can be increased upto 63)
GUI (Graphical User Interface): by default 1 (can be increased 33/34)

You can switch between virtual terminals by just press the ALT+CTRL+Funcation key combinations.

ALT + CTRL + F1  for terminal 1
ALT + CTRL + F2  for terminal 2
ALT + CTRL + F3  for terminal 3
ALT + CTRL + F4  for terminal 4
ALT + CTRL + F5  for terminal 5
ALT + CTRL + F6  for terminal 6
ALT + CTRL + F7  for terminal 7

Terminal 7 is by default graphic mode beside it all six terminal are CLI based. Open any terminial by press ALT+CTRL+F1 key combinations.

Kernel: Package, Program etc.

The kernel is the heart of Operating system or we can say a core part of an Operating system which provide the interaction between OS and hardware. It is responsible to run each and every process in the system.

Note:

1970: Dos launched by a third person and brought by Microsoft
(in reverse revenue should have been given to him but not given)
1983: Windows launched by Microsoft
In September 2008 Microsoft CEO Steve Ballmer admitted that 60% of web-servers run Linux versus 40% that run Windows Server.
Desktop market 1 to 2 % of linux and more than 85 % of Windows.
GNU (GNU's Not Unix): To create a Unix like OS
GPL: General Public License
FSF: Free Software Foundation
Finally a kernel Minix (mini unix) was developed

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