CompTIA Linux+ What is Linux?

Linux is a 32 bit open source operating system. It is based on the very popular Unix operating system and it’s code is freely available (thus explaining the “open source” label as opposed to closed source where the code is not available freely). Linux is often referred to as being a “gathering of very cool software”. While this is not a bad description, a more precise definition would reveal that Linux refers to a specific part of the “gathering”. Linux points to it’s most basic element: the kernel. Everything else that is bundled with the Linux you get is an application.

 

The Linux kernel is the operating system itself. There are different versions and they are released by a non-profit organization using a version number system. Each time something is added to the kernel, a new beta or experimental version is released. Generally, there can be up to 11 latest versions of the kernel available.

 

 

The main ones being:

The last thing to know about kernel versions is the way the numbers are being assigned. For a X.Y.ZZ version, X would represent a major release version. Y is a minor release version and Z is a patch version number. In other words, when a bug is found and a patch released, only the Z number will change. When a bunch of new features are implemented and the need to do an upgrade is done, the Y number is changed and finally, when a collection of upgrades have been done, when a major improvement or code revision has been done, the X number will be revised. To learn more about kernel versions, make sure to visit www.kernel.org.

 

 

Here are some examples (at the time of this writing):

The latest stable Linux kernel tree is: 2.4.19
The latest prepatch for the stable Linux kernel tree is: 2.4.20-pre11
The latest beta version of the Linux kernel is: 2.5.44
The latest prepatch for the beta Linux kernel tree is: 2.5.8-pre3
The latest 2.2 version of the Linux kernel is: 2.2.22
The latest prepatch for the 2.2 Linux kernel tree is: 2.2.22-rc3
The latest -ac patch to the stable Linux kernels is: 2.4.20-pre10-ac2
The latest -ac patch to the beta Linux kernels is: 2.5.44-ac3
The latest -dj patch to the beta Linux kernels is: 2.5.39-dj2

 

 

 

Distributions
As mentioned before, Linux is often distributed in different formats; there exists many like it, each of them being bundled with loads of software by different companies or non-profit organizations. These formats are called distributions. They include a kernel and a collection of applications, software, wizards and specific tools.

 

 

Packaging
Originally, open source software like Linux was provided as source code. While this had interesting features, only hardcore developers could handle, compile and play with the necessary files. Soon, binary files were available and usually shipped with easy to follow instructions to compile them. Such instruction are usually found in a Makefile which is generally a simple set of scripts and instructions.

 

 

Even though source code is always available, binary files are now the most current way to handle program installation in Linux. By using special applications, it is possible to handle the installation of binaries without hard user intervention. However, the format in which they are provided can differ from one to another. Especially since some popular distributions have developed their own proprietary systems to resolve packaging problems. For the exam, you should know the major packaging solutions and some of their specific attributes. Here are some examples:

Licensing
Licensing in the Linux world is quite easy to understand. The software, applications and even the kernel will fall under one of the following license mode:

Linux Command Prompt
The Linux command Prompt is called the Shell. Just as the DOS shell is identified by a group of characters (C:\), the Linux shell is identified by its own set of characters. Many different shells exist. The most commonly used is probably Bash (Bourne Again Shell), but there are many others. Shells will vary with distributions or users’ taste.

 

To find out what your shell is type the echo $SHELL command.

 

 

 

 

 

Daemons
A daemon is more or less the Linux equivalent of a windows service. It is an automated process that manages resources, processes, etc.

 

 

Man pages
The man command is a small command utility that outputs information about a Linux command. This information is generally known as a “man page”. To learn more about the man command, simply type man man.

 

 

Case Sensitive
For many reasons including security reasons, Linux is a highly case sensitive operating system. New users often encounter frustration when typing in commands because they tend to forget this little detail!

 

 

Source By:<www.mcmcse.com>

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