LINUX system

Linux is a free and open-source UNIX-like operating system. It is a multi-user, multi-tasking and time sharing operating system. Linux is a very stable OS and is used in many application areas, such as by Internet Service Providers (ISPs) and as a network OS for providing various services.

In the early 1990s, a Finnish student at the University of Helsinki named Linus Torvalds became fed up with the operating system choices available. Linus wanted to use Unix, but unfortunately or fortunately, depending on how you see it, Unix was far too expensive for a student. Left with only one choice, Linus started to build his kernel “Just for fun”1 from scratch.

The kernel of this operating system was first release by Linus Torvalds in 1991. After that, with the addition of user space applications, it became the Linux operating system. Linux source code is freely available and it is community based development project. Multiple teams’ works in collaboration to enhance the capability of Linux operating system and it is continuously evolving.

Linux is well-known as a stable and reliable platform, providing database and trading services for companies like Amazon, the well-known online bookshop, US Post Office, the German army and many others. Especially Internet providers and Internet service providers have grown fond of Linux as firewall, proxy- and web server.

Modern Linux not only runs on workstations, mid- and high-end servers, but also on "gadgets" like PDA's, mobiles, a shipload of embedded applications and even on experimental wristwatches.

There are 5 types of users available in Linux.
(i) System user (Admin user who control the whole system nothing but root user).
(ii) Normal user (Created by the Super user. In RHEL - 7 the user id's from 1000 - 60000).(iii) System user (Created when application or software installed ).(In RHEL - 7 the System users are Static system user id's from 1 - 200 and(
(iii) Dynamic system user user id’s from 201 - 999).
(iv) Network user (Nothing but remote user, ie., who are login to the system trough network created in Windows Active Directory or in Linux LDAP or NIS).
(v) Sudo user (The normal users who are having admin or Super user privileges)
LINUX system

UNIX operating system

The UNIX operating system is a set of programs that act as a link between the computer and the user. The origin of UNIX can be traced back to 1965, when a joint venture was under-taken by Bell Telephone Laboratories, the General Electric Company and Massachusetts Institute of Technology. The first Unix OS was developed by Ken Thompson and Dennis Ritchie at Bell Laboratories in 1969.

UNIX is written in high-level language. About 95% of the OS is written in C programming language. 'C' making it easy to port to different configurations. The ability to transport the UNIX system from one brand of computer to another has been the major reason for the acceptance of this system.

It uses a hierarchical file system that allows easy maintenance and efficient implementation. UNIX uses a consistent format for files, the byte stream, making application programs easier to write.

The main features of UNIX include multiuser, multitasking and portability capabilities. Multiple users access the system byconnecting to points known as terminals. Several users can run multiple programs or processes simultaneously on one system.

UNIX is now a family of operating systems:
– AIXfrom IBM
– HP-UXfrom Hewlett-Packard
– GNULinux from Free Software Foundation
– Solaris, SunOSfrom Sun Microsystems
UNIX operating system

Multi-user operating system

Operating systems may be single user, like a typical PC at home, or multi-user, where more than one person (usually many more) can use the same computer at apparently the same time.

Multi-user operating system can be defined as an operating system that can handle more than one user concurrently. Concurrent service of requests does not necessarily mean that the requests are serviced simultaneously. Instead, to the users they appear to be serviced at the same time.

The advantage of using multi-user operating system is that it facilitates the sharing of data and information among different users.

Multi-user operating systems are very similar to multi-tasking operating system. On the other hand, multi-tasking typically refers to system in which the tasks interact, while multi-user systems generally try to isolate the various tasks.

It allows multi-user to use programs that are simultaneously running on a single network server, called a terminal server.

A dedicated transaction processing system such as railway reservation system that supports hundreds of terminal under control of a single program is an example of multi-user operating system.
Multi-user operating system

What is operating system?

Operating system is the most important piece of software in a computer. The operating system is the software responsible for mediating the control of all three families of the computer’s resources: hardware, software and data.

The operating system s control how the system works. Controls the running of programs and provides such services as resource allocation, scheduling, input, and out control and data management.

The fundamental task is to control interaction among users and also between users and system services. Performance is a critical factor of all facets of an operating system. All the important parts of the operating system such as memory management, process and thread scheduler, file I/O and communication protocol should work as efficiently as possible.
What is operating system?

Multiprogramming operating systems

In batch operating system, the jobs are submitted in the batch and all the resources are reserved to one job at a time. This drawback of batch operating system may be overcome by multiprogramming operating systems.

When two or more programs are in memory at the same time, sharing the processor is referred to the multiprogramming operating system. Time sharing is a special case of multiprogramming where a single CPU serves a number of users at the interactive terminals.

Multiprogramming assumes a single processor that is being shared. Multiprogramming operating system monitors the state of all active programs and system resources. This ensures that the CPU is never idle unless there are no jobs.

In a multiprogramming system, several programs are in a state of partial completion at any time. Resources allocated to a program are utilized when the program is executed.

Multiprogramming improves both system throughout and resource utilization. The job submitted to the operating system requires CPU for computation and I/O for their I/O needs.

There are three different forms of multiprogramming operating system:
*Multitasking operating system
*Multiuser operating system
*Multiprocessing operating system
Multiprogramming operating systems

System Software

System software consists of programs that are used to control and operate the computer hardware.

System software is not application specific; it is oriented to the needs of the hardware and facilities the development and running of application.

There are three components in system software: operating system, utility programs and language processors. System software serves as the interface between the user, the application software and the computer’s hardware.

The operating system present in all computers except for a few very specialized applications. These programs enable the computer to boot, to launch application programs and to facilitate important jobs such as how to transfer data between input/output devices and to manage resources available (CPU).

The operating system must be loaded in the main memory before the computer can function. Other application software can then be loaded into the computer with the help of the operating system.
System Software

Definition of Operating System

An operating system is a program or software that controls the execution of application programs and acts as an interface between the user of a computer and the computer hardware.

To be more specific, the operating system is used to control the hardware memory, schedule the execution of programs, and schedule input output traffic between the CPU and other devices.

Operating systems are designed to present the various hardware resources of a computer to software and to a user.

A good operating system, can dramatically improve the effectiveness and the efficiency of program execution performance.

Every computer must have an operating system to run other program. The operating system controls and coordinates the use of the hardware among the various system programs an application program for a various users.

The operating system boots the computer, launches application software programs and ensures that all actions required by a user are valid and processed in orderly fashion.

Some operating systems are designed for a microcomputer single user environment, and others are for multiple users.

The complexity of operating system is much higher in a multiple user operating system due to the management of computer memory and CPU time shared by many users.

Different sizes of computers typically use different operating systems because operating systems generally are written to run on a specific type of computer. For example, a mainframe computer does not use the same operations system as personal computer.

Today, many computers use what is called an operating environment, which provides end users with a user friendly interface to use.

Definition of Operating System