undefined | unit 5 case study

UNIT 5

Case Study

Q1) What is Linux? Write short notes.

A1) Just like Windows, iOS, and Mac OS, Linux is an operating system. In fact, one of the most popular platforms on the planet, Android, is powered by the Linux operating system. An operating system is software that manages all of the hardware resources associated with your desktop or laptop. To put it simply, the operating system manages the communication between your software and your hardware. Without the operating system (OS), the software wouldn?t function.

The Linux operating system comprises several different pieces:

Bootloader – The software that manages the boot process of your computer. For most users, this will simply be a splash screen that pops up and eventually goes away to boot into the operating system.

Kernel – This is the one piece of the whole that is actually called ?Linux?. The kernel is the core of the system and manages the CPU, memory, and peripheral devices. The kernel is the lowest level of the OS.

Init system – This is a sub-system that bootstraps the user space and is charged with controlling daemons. One of the most widely used init systems is systemd? which also happens to be one of the most controversial. It is the init system that manages the boot process, once the initial booting is handed over from the bootloader (i.e., GRUB or GRand Unified Bootloader).

Daemons – These are background services (printing, sound, scheduling, etc.) that either start up during boot or after you log into the desktop.

Graphical server – This is the sub-system that displays the graphics on your monitor. It is commonly referred to as the X server or just X.

Desktop environment – This is the piece that the users actually interact with. There are many desktop environments to choose from (GNOME, Cinnamon, Mate, Pantheon, Enlightenment, KDE, Xfce, etc.). Each desktop environment includes built-in applications (such as file managers, configuration tools, web browsers, and games).

Applications – Desktop environments do not offer the full array of apps. Just like Windows and macOS, Linux offers thousands upon thousands of high-quality software titles that can be easily found and installed. Most modern Linux distributions (more on this below) include App Store-like tools that centralize and simplify application installation. For example, Ubuntu Linux has the Ubuntu Software Center (a rebrand of GNOME Software? Figure 1) which allows you to quickly search among the thousands of apps and install them from one centralized location.

Q2) Why use Linux?

A2) This is the one question that most people ask. Why bother learning a completely different computing environment, when the operating system that ships with most desktops, laptops, and servers works just fine?

To answer that question, I would pose another question. Does that operating system you?re currently using really work ?just fine?? Or, do you find yourself battling obstacles like viruses, malware, slow downs, crashes, costly repairs, and licensing fees?
If you struggle with the above, Linux might be the perfect platform for you. Linux has evolved into one of the most reliable computer ecosystems on the planet. Combine that reliability with zero cost of entry and you have the perfect solution for a desktop platform.

That’s right, zero cost of entry… as in free. You can install Linux on as many computers as you like without paying a cent for software or server licensing.

Let’s take a look at the cost of a Linux server in comparison to Windows Server 2016. The price of the Windows Server 2016 Standard edition is $882.00 USD (purchased directly from Microsoft). That doesn’t include Client Access License (CALs) and licenses for other software you may need to run (such as a database, a web server, mail server, etc.). For example, a single user CAL, for Windows Server 2016, costs $38.00. If you need to add 10 users, for example, that’s $388.00 more dollars for server software licensing. With the Linux server, it?s all free and easy to install. In fact, installing a full-blown web server (that includes a database server), is just a few clicks or commands away (take a look at ?Easy LAMP Server Installation? to get an idea how simple it can be).

If zero cost isn’t enough to win you over? what about having an operating system that will work, trouble free, for as long as you use it? I’ve used Linux for nearly 20 years (as both a desktop and server platform) and have not had any issues with ransomware, malware, or viruses. Linux is generally far less vulnerable to such attacks. As for server reboots, they’re only necessary if the kernel is updated. It is not out of the ordinary for a Linux server to go years without being rebooted. If you follow the regular recommended updates, stability and dependability are practically assured.

Q3) What is a “distribution?”

A3) Linux has a number of different versions to suit any type of user. From new users to hard-core users, you’ll find a “flavor” of Linux to match your needs. These versions are called distributions (or, in the short form, “distros”). Nearly every distribution of Linux can be downloaded for free, burned onto disk (or USB thumb drive), and installed (on as many machines as you like).

Popular Linux distributions include:

LINUX MINT

MANJARO

DEBIAN

UBUNTU

ANTERGOS

SOLUS

FEDORA

ELEMENTARY OS

OPENSUSE

Each distribution has a different take on the desktop. Some opt for very modern user interfaces (such as GNOME and Elementary OS’s Pantheon), whereas others stick with a more traditional desktop environment (openSUSE uses KDE).

And don’t think the server has been left behind. For this arena, you can turn to:

Red Hat Enterprise Linux

Ubuntu Server

Centos

SUSE Enterprise Linux

Some of the above server distributions are free (such as Ubuntu Server and CentOS) and some have an associated price (such as Red Hat Enterprise Linux and SUSE Enterprise Linux). Those with an associated price also include support.

Q4) Which distribution is right for you?

A4) Which distribution you use will depend on the answer to three simple questions:

a) How skilled of a computer user are you?

b) Do you prefer a modern or a standard desktop interface?

c) Server or desktop?

If your computer skills are fairly basic, you’ll want to stick with a newbie-friendly distribution such as Linux Mint, Ubuntu (Figure 3), Elementary OS or Deepin. If your skill set extends into the above-average range, you could go with a distribution like Debian or Fedora. If, however, you’ve pretty much mastered the craft of computer and system administration, use a distribution like Gentoo. If you really want a challenge, you can build your very own Linux distribution, with the help of Linux From Scratch.

If you’re looking for a server-only distribution, you will also want to decide if you need a desktop interface, or if you want to do this via command-line only. The Ubuntu Server does not install a GUI interface. This means two things your server won’t be bogged down loading graphics and you’ll need to have a solid understanding of the Linux command line. However, you can install a GUI package on top of the Ubuntu Server with a single command like sudo apt-get install ubuntu-desktop. System administrators will also want to view a distribution with regards to features. Do you want a server-specific distribution that will offer you, out of the box, everything you need for your server? If so, CentOS might be the best choice. Or, do you want to take a desktop distribution and add the pieces as you need them? If so, Debian or Ubuntu Linux might serve you well.

Q5) Explain Linux Design Principles.

A5) As a result of the development of PC technology, the Linux kernel is also becoming more complete in implementing UNIX functions. Fast and efficient are important design goals, but lately the concentration of Linux development has focused more on the third design goal, standardization. The POSIX standard consists of a collection of specifications from different aspects of operating system behavior. There are POSIX documents for ordinary operating system functions and for extensions such as processes for threads and real-time operations. Linux is designed to fit the relevant POSIX documents; there are at least two Linux distributions that have received POSIX official certification.

Because Linux provides a standard interface to programmers and users, Linux does not make many surprises to anyone who is familiar with UNIX. But the Linux programming interface refers to the UNIX SVR4 semantics rather than BSD behavior. A different collection of libraries is available to implement the BSD semantics in places where the two behaviors are very different.

There are many other standards in the UNIX world, but Linux’s full certification of other UNIX standards sometimes becomes slow because it is more often available at a certain price (not freely), and there is a price to pay if it involves certification of approval or compatibility of an operating system with most standards . Supporting broad applications is important for all operating systems so that the implementation of the standard is the main goal of developing Linux even though its implementation is not formally valid. In addition to the POSIX standard, Linux currently supports POSIX thread extensions and subsets of extensions for POSIX real-time process control.

Q6) Explain in detail Linux System Components.

A6) The Linux system consists of three important code parts:

Kernel: Responsible for maintaining all important abstractions of the operating system, including things like processes and virtual memory.

System library: defines a set of standard functions where applications can interact with the kernel, and implements almost all operating system functions that do not require full rights to the kernel.

System Utility: is a program that performs management work individually and specifically.

Kernel:

Although various modern operating systems have adopted a message-passing architecture for their internal kernel, Linux uses the historical UNIX model: the kernel was created as a single, monolithic binary. The main reason is to improve performance: Because all data structures and kernel code are stored in one address space, context switching is not needed when a process calls an operating system function or when a hardware interrupt is sent. Not only scheduling core and virtual memory code occupies this address space; all kernel code, including all device drivers, file systems, and network code, come in the same address space.

The Linux kernel forms the core of the Linux operating system. It provides all the functions needed to run the process, and is provided with system services to provide settings and protection for access to hardware resources. The kernel implements all the features needed to work as an operating system. However, if alone, the operating system provided by the Linux kernel is not at all similar to UNIX systems. It does not have many extra UNIX features, and the features provided are not always in the format expected by the UNIX application. The interface of the operating system that is visible to the running application is not maintained directly by the kernel. Instead, the application makes calls to the system library, which then invokes the operating system services that are needed.

System Library:

The system library provides many types of functions. At the easiest level, they allow applications to make requests to the kernel system services. Making a system call involves transferring controls from non-essential user mode to important kernel mode; the details of this transfer are different for each architecture. The library has the duty to collect system-call arguments and, if necessary, arrange those arguments in the special form needed to make system calls.

Libraries can also provide more complex versions of basic system calls. For example, the buffered file-handling functions of the C language are all implemented in the system library, which results in better control of file I / O than those provided by the basic kernel system call. The library also provides routines that have nothing to do with system calls, such as sorting algorithms, mathematical functions, and string manipulation routines. All functions needed to support the running of UNIX or POSIX applications are implemented in the system library.

System Utilities:

Linux systems contain many user-mode programs: system utilities and user utilities. The system utilities include all the programs needed to initialize the system, such as programs for configuring network devices or for loading kernel modules. Server programs that are running continuously are also included as system utilities; This kind of program manages user login requests, incoming network connections, and printer queues.

Not all standard utilities perform important system administration functions. The UNIX user environment contains a large number of standard utilities for doing daily work, such as making directory listings, moving and deleting files, or showing the contents of a file. More complex utilities can perform text-processing functions, such as compiling textual data or performing pattern-searches on text input. When combined, these utilities form the standard toolset expected by users on any UNIX system; even if it doesn’t perform any operating system functions, utilities are still an important part of a basic Linux system.

Q7) What is Process Scheduling and what is process scheduling queues?

A7) Process Scheduling is an OS task that schedules processes of different states like ready, waiting, and running.

Process scheduling allows OS to allocate a time interval of CPU execution for each process. Another important reason for using a process scheduling system is that it keeps the CPU busy all the time. This allows you to get the minimum response time for programs.

Process Scheduling Queues

Process Scheduling Queues help you to maintain a distinct queue for each and every process states and PCBs. All the process of the same execution state are placed in the same queue. Therefore, whenever the state of a process is modified, its PCB needs to be unlinked from its existing queue, which moves back to the new state queue.

Three types of operating system queues are:

Job queue – It helps you to store all the processes in the system.

Ready queue – This type of queue helps you to set every process residing in the main memory, which is ready and waiting to execute.

Device queues – It is a process that is blocked because of the absence of an I/O device.

In the above-given Diagram,

Rectangle represents a queue.

Circle denotes the resource

Arrow indicates the flow of the process.

Every new process first put in the Ready queue .It waits in the ready queue until it is finally processed for execution. Here, the new process is put in the ready queue and wait until it is selected for execution or it is dispatched.

One of the processes is allocated the CPU and it is executing

The process should issue an I/O request

Then, it should be placed in the I/O queue.

The process should create a new subprocess

The process should be waiting for its termination.

It should remove forcefully from the CPU, as a result interrupt. Once interrupt is completed, it should be sent back to ready queue.

Q8) What are the types of process schedulers?

A8) Type of Process Schedulers

A scheduler is a type of system software that allows you to handle process scheduling.

There are mainly three types of Process Schedulers:

Long Term .

Short Term.

Medium Term .

Long Term Scheduler:

Long term scheduler is also known as a job scheduler. This scheduler regulates the program and select process from the queue and loads them into memory for execution. It also regulates the degree of multi-programing.

However, the main goal of this type of scheduler is to offer a balanced mix of jobs, like Processor, I/O jobs., that allows managing multiprogramming.

Medium Term Scheduler:

Medium-term scheduling is an important part of swapping. It enables you to handle the swapped out-processes. In this scheduler, a running process can become suspended, which makes an I/O request.

A running process can become suspended if it makes an I/O request. A suspended processes can't make any progress towards completion. In order to remove the process from memory and make space for other processes, the suspended process should be moved to secondary storage.

Short Term Scheduler:

Short term scheduling is also known as CPU scheduler. The main goal of this scheduler is to boost the system performance according to set criteria. This helps you to select from a group of processes that are ready to execute and allocates CPU to one of them. The dispatcher gives control of the CPU to the process selected by the short term scheduler.

Q9) Difference between Schedulers

A9) Long-Term Vs. Short Term Vs. Medium-Term

Long-Term	Short-Term	Medium-Term
Long term is also known as a job scheduler	Short term is also known as CPU scheduler	Medium-term is also called swapping scheduler.
It is either absent or minimal in a time-sharing system.	It is insignificant in the time-sharing order.	This scheduler is an element of Time-sharing systems.
Speed is less compared to the short term scheduler.	Speed is the fastest compared to the short-term and medium-term scheduler.	It offers medium speed.
Allow you to select processes from the loads and pool back into the memory	It only selects processes that is in a ready state of the execution.	It helps you to send process back to memory.
Offers full control	Offers less control	Reduce the level of multiprogramming.

Q10) What is CPU Scheduling and what are its types?

A10) CPU Scheduling is a process of determining which process will own CPU for execution while another process is on hold. The main task of CPU scheduling is to make sure that whenever the CPU remains idle, the OS at least select one of the processes available in the ready queue for execution. The selection process will be carried out by the CPU scheduler. It selects one of the processes in memory that are ready for execution.

Types of CPU Scheduling

Here are two kinds of Scheduling methods:

Preemptive Scheduling

In Preemptive Scheduling, the tasks are mostly assigned with their priorities. Sometimes it is important to run a task with a higher priority before another lower priority task, even if the lower priority task is still running. The lower priority task holds for some time and resumes when the higher priority task finishes its execution.

Non-Preemptive Scheduling

In this type of scheduling method, the CPU has been allocated to a specific process. The process that keeps the CPU busy will release the CPU either by switching context or terminating. It is the only method that can be used for various hardware platforms. That's because it doesn't need special hardware (for example, a timer) like preemptive scheduling.

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