Operating System

Operating system

   It is the system software which provides interface to the user and also coordinates the software and hardware components of the system.

     Types of operating systems

      Within the broad family of operating systems, there are generally four types, categorized based on the types of computers they control and the sort of applications they support. The categories are:

• Real-time operating system (RTOS)

Real-time operating systems are used to control machinery, scientific instruments and industrial systems. An RTOS typically has very little user-interface capability, and no end-user utilities, since the system will be a "sealed box" when delivered for use. A very important part of an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time, every time it occurs. In a complex machine, having a part move more quickly just because system resources are available may be just as catastrophic as having it not move at all because the system is busy.

• Single-user, single task

 As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS for Palm handheld computers is a good example of a modern single-user, single-task operating system.

• Single-user, multi-tasking–

This is the type of operating system most people use on their desktop and laptop computers today. Microsoft's Windows and Apple's MacOS platforms are both examples of operating systems that will let a single user have several programs in operation at the same time. For example, it's entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the Internet while printing the text of an e-mail message.

• Multi-user

 A multi-user operating system allows many different users to take advantage of the computer's resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.

It's important to differentiate between multi-user operating systems and single-user operating systems that support networking. Windows 2000 and Novell Netware can each support hundreds or thousands of networked users, but the operating systems themselves aren't true multi-user operating systems. The system administrator is the only "user" for Windows 2000 or Netware. The network support and all of the remote user logins the network enables are, in the overall plan of the operating system, a program being run by the administrative user.

Examples of operating systems

Some examples include versions of Microsoft Windows (like Windows 10, Windows 8, Windows 7, Windows Vista, and Windows XP), Apple's macOS (formerly OS X) Chrome OS, and flavors of the open source operating system Linux.

Introduction to Linux

What is Linux ?

Linux is an operating system , Linux mainly runs on the database servers, web servers, virtualization server etc.

History of Linux

Linux was created in 1991 to 1994, by Linus Torvalds this project made him created a new level of operating system, in the Linux most of commands looks like Unix. But Linux and Unix was its own type of operating system. Linus created the Linux from it ground and reason he want to make it open source and he also made the code to see everyone in this world.

Distributions of Linux

Distributions is nothing but different versions  of Linux operating systems.

1. Redhat Linux
2. Ubuntu
3. Centos
4. Fedora
5. Google android etc.

And there are over 100’s of Linux distributions available in the market now

In the Linux every distribution as its own features, in the Linux there is distribution called Trustix Secure Linux was intended for use on servers and focused on security and stability. Trustix Secure Linux includes the open standards based SoftWare UPdater, SWUP, which keeps all software packages up-to-date, resolves library dependencies and integrates public key cryptography to ensure safety and security. 

The Shell

Computers understand the language of zeros and ones known as binary language. In the early days of computing, instructions were provided using binary language, which is difficult for all of us to read and write. Therefore, in an operating system there is a special program called the shell. The shell accepts human readable commands and translates them into something the kernel can read and process.

The shell is a command prompt in the Linux where you can the type the commands.

 Different types of shells

Bourne Shell - This is the oldest shell and as such is not as feature rich as many of the other shells. It's feature set is sufficient for most programming needs however it does not have some of the user conveniences that are liked on the command line. There is no option to re-edit previous commands or to control background jobs. As the bourne shell is available on all UNIX systems it is often used for programming script files as it offers maximum portability between different UNIX versions. Bash is fully backwards compatible with the Bourne Shell so running the bourne shell on Linux will often call the bash shell (using a link between the files).

Korn Shell - This is based on the Bourne shell. One enhancement that is particularly useful is its command-line editing facility. It is possible using either vi or emacs keys to recall and edit previous commands. This is not as easy to use as some of the other shells, but work well across a network or using a physical terminal (rare these days). It also has more powerful programming constructs than the bourne shell, however these are not as portable. To run the Korn shell you can run either ksh or pdksh from the normal shell (assuming it is installed).

C Shell - The c shell syntax is taken from the C programming language. As such it is a useful tool for anyone familiar with programming C.

Bash Shell - The Bash shell is a combination of features from the Bourne Shell and the C Shell. It's name comes from the Bourne Again SHell. It has a command-line editor that allows the use of the cursor keys in a more "user friendly" manner than the Korn shell. It also has a useful help facility allowing you to get a list of commands by typing the first few letters followed by the "TAB" key. It is the default shell on most Linux distributions and unless otherwise specified is the shell used for the future examples.

tcsh - This is a different shell that emulates the C Shell. It has a number of enhancements and further features even than the bash shell. 

The different layers of the Linux operating system. 

The kernel is the heart of the operating system. This is the bit that is actually Linux. The kernel is a process that runs continuously managing the computer. The kernel is a very specific task so to allow programs to communicate with it there are a number of low level utilities that provide an interface between the application and the kernel.

The shell is an application that allows users to communicate with the computer. It is a text based application that allows programs to be started and tasks to be run. The shell is within a collections of utilities known as GNU. Without the kernel the computer cannot run and without the GNU utilities it can't do anything useful which is why the operating system is sometimes called GNU/Linux; although this ignores the host of other applications that are also included (for brevity I am just using Linux to mean everything included on the Linux distribution).

ROOT

Root is the user in the Linux and it is the administrator, if you log in as the root user we can do anything and what we want in the computer. Operating system is installed in the root user, in the Linux home is the directory every user.

Capitalization

Basically in the alphabets we have uppercase and lowercase letters, windows doesn’t care whatever the case we used but it’s different in the case of Linux all this will be dependent on ASCII stands for American Standard Code for Information Interchange.

Every Linux distro has two versions  i.e Server and Desktop 

Server

Server is a computer program that provided services to the other computer programs in the same or other computers.

In the client server architecture, there server responds when the client requests a request. And it waits till the request placed by the user.

Examples of the servers

Mail server, Application server, Proxy Server , Virtual server , File server and Policy server etc….

Desktop

Desktop version is nothing but what we are going to use in our devices.