Scl 3 The Advantages and disadvantages of LINUX

The Advantages of LINUX OS

It’s not that hard to use	Many Linux distributions use graphical interfaces that look and work much the same way as the Windows interface does. In fact, a 2003 study by Relevantive, a Berlin-based company specializing in consulting companies on the usability of software and Web services, rated Linux almost as easy to use as Windows XP.
Less viruses	Windows currently has over a hundred thousand known viruses, while Linux has less than a hundred. Linux also uses smart authorisation management , so it requires you to authorise any action that may potentially harm your computer by entering your password. That means you are less likely to be tricked into installing malware and running virus programs, simply because it won’t let you.
No crashes	Windows users will be familiar with the infamous “blue screen of death” that greets them whenever the system crashes. In contrast, Linux users have reported uptimes exceeding over a year, which means that their computers have been continuously running over a year without a single crash or reboot.
Tech support	Get round-the-clock support when using Linux. You don’t have to make any calls; simply visit any of the Linux online forums and post the problem there. The Linux community is very active and generally friendly and helpful, so expect the solution to be posted within a day or two. Or do some forum surfing; your problem will most probably have been faced by other beginners before and already solved, so Google your specific problem first to find if there are previous forum threads solving it.
Free software	Linux users can download free software from huge repositories containing thousands of free programs and applications, from games to music players to office productivity tools. Most of them serve as free alternatives to commercial software, the most popular ones being OpenOffice and Mozilla Firefox, which replace Microsoft Office and Internet Explorer respectively.
Runs on old machines	Many new computers in the market still struggle to handle the memory and capacity demands of Vista, which requires 512MB RAM and a 800MHz processor. In contrast, the latest Ubuntu version, the Feisty Fawn, needs a measly 64MB RAM and a 300MHz processor. Other versions of Linux require even less. That means you can run Linux on your ten-year-old PC without a hitch.

The disadvantages of LINUX

Incompatibility issues

Because many hardware and software publishers deem the market for Linux users too small, you may encounter some incompatibility issues when installing programs or devices like printers. Many devices are supported though, and, as mentioned above, there are free alternatives to proprietary programs that are available for download. As a general rule of thumb, if two or more of your devices are not supported by a particular version of Linux, install another version.

Different working mechanism

If you’re a lifelong Windows user, you may take a while to get used to the way Linux works. From installing software to running programs, things are a little different in Linux-based systems. Be prepared to type a few new commands as well. However, there are programs within some versions of Linux, such as Ubuntu, which help you to download and install programs with just a few clicks. Most people take about a week to familiarise themselves to the new virtual surroundings.

SCL 3,QUESTION 1(HOW OPERATING SYSTEM WORKS - LINUX AND UNIX)

Linux and UNIX Operating System

What is Linux?

Linux is operating system for laptop/dekstop that assembled under the model of free and open software. It was created by Linus Torvalds.

Linus Torvalds

How Linux operating system works

Boot loader

This is the part of the system that is executed first. When you have only one operating system installed, it simply loads the kernel. If you happen to have multiple operating systems or multiple versions of the Linux kernel installed, it allows you to choose which one you want to start. The most popular bootloaders are GRUB (GRand Unified Bootloader) and LILO (LInux LOader). Most users don't need to care about the boot loader, because it is installed and configured automatically.

Kernel

The kernel is the central component of the system that communicates directly with the hardware. In fact, the name "Linux" properly refers to a particular kind of this piece of software. It allows programs to ignore the differences between various computers. The kernel allocates system resources like memory, processor time, hard disk space and external devices to the programs running on the computer. It separates each program from the others, so that when one of them encounters an error, others are not affected. Most users don't need to worry about the kernel in day-to-day use, but certain software or hardware will require or perform better with certain kernel versions.

Shell

The shell is a textual interface that allows you to run programs and control the system by entering commands from the keyboard. Without a shell (or something that can replace it, like a desktop environment) it would be hard to make your system actually do something. The shell is just a program - there are several different shells for Linux, each of them offering different features. Most Linux systems use the Bourne Again Shell (Bash). Linux shells support multitasking (running several programs at once).

X Window Server

The X window server is a graphical replacement of the command shell. It is responsible for drawing graphics and processing input from the keyboard, mouse, tablets and other devices. The X server is network transparent, that is, it allows you to work in a graphical environment both on your own computer as well as on a remote computer that you connect to across a network. The X server that is most used today is X.Org. Most graphical programs will only need the X server to run, so you can use them under any window manager and desktop environment.

Window Manager

The window manager is a program that communicates with the X server. Its task is managing windows. It is responsible for drawing the window borders, bringing a window to the front when you click it, moving it on the screen and hiding them when you minimize a program. Examples of popular window managers are:

• Metacity - GNOME Desktop Environment window manager
• Kwin - KDE window manager
• Xfwm- Xfce window manager, a lightweight manager designed to consume as little resources as possible without compromising usability
• Compiz Fusion - an advanced window manager with lots of eye candy like customizable window animations, multiple desktops placed on a cube that you can rotate with your mouse, transparent window borders, wobbling windows while dragging them, etc.

Window manager of LINUX

Desktop Environment

Desktop environments, like GNOME Dekstop Environment, KDE and Xfec, are collections of programs designed to present a consistent user interface for most common tasks. This is the thing most people think about when they say "operating system" even though it is only a piece of the larger operating system. Replacing the desktop environment is a rather complex task, so most new users should stay with the default environment offered by their distribution.

File System

There are several file systems that Linux-based distributions use. They are BTRFS, EXT3/4, VFS, NILFS, and SquashFS.

The hard drive of your computer has a rather simple interface. It only accepts commands like "read block no. 550923 and put it in memory address 0x0021A400". Let's assume you are editing a piece of text and want to save it on the disk. Using block numbers (addresses) to identify pieces of data, like your text, is rather awkward. You would have to tell the program to save the file i.e. in blocks from 239012 to 239088. You would also have to remember what data you have stored where, so that you won't overwrite your family photo, your music collection or even your system's kernel. To solve this problem, the concept of a file was introduced - that is, a named area of disk storing some data. To organise files, they are collected in directories. Directories can contain other directories, which gives us a tree-like structure. Each file can be uniquely identified by a path, which describes its place in the directory hierarchy. For the remainder of this section, it will be assumed that you are familiar with files, directories and paths.

In Linux, the top-level directory is called the root directory and denoted with a forward slash: "/". Every file and directory in the system must be a descendant of the root directory (it is common to talk about directories using the terminology of family relations, like "parent", "child", "descendant", "ancestor", "sibling", etc.). Directories are separated with "/". Names of directories and files can contain all characters except "/" and the null character (you don't need to care about it, because it is impossible to enter from the keyboard). An example path would be:/var/logs/apache/error.log

This path refers to a file called "error.log" which is found in a directory called "apache", which is a subdirectory of a directory called "logs", which is subdirectory of a directory called "var", which is a subdirectory of the root directory (/).

The root directory usually contains only a small number of subdirectories. The most important are:

• bin - programs needed to perform basic tasks, i.e. change a directory or copy a file
• dev - special files that represent hardware devices
• etc - configuration files
• home - contains private directories of users
• media or mnt - Mount point for external drives connected to this computer, i.e. CDs or USB keys
• tmp - temporary files
• usr - programs installed on the computer
• var - variable data produced by programs, like error logs

Devices as files

Just as files can be written to and read, devices in the computer system may send and receive data. Because of this, Linux represents the devices connected to the system as files in the /devdirectory. These files can not be renamed or moved (they are not stored on any disk). This approach greatly simplifies application programming. If you want to send something to another computer through a serial port, you don't even need another program - you simply write to the file /dev/ttyS0, which represents a serial port. In the same manner the file representing the sound card (/dev/dsp) can be read to capture the sound from an attached microphone, or written to in order to produce sound through the speakers.

Where are the drive letters?

If you have used Windows, you might be surprised that there are no drive letters in Linux. The root directory represents the drive on which the system is installed (C: in Windows). Other drives can be "mounted" or "unmounted" in any directory (preferably, an empty one) in the file system. By mounting a disk, you attach the root directory of this disk to a directory in the file system. After that, you can access the disk like it were a part of your system disk. For example: if you have a disk that contains a directory text, which in turn contains a file called linux-intro.tex and you mount this drive in the directory /media/usbkey, you can access the file linux-intro.tex through the path /media/usbkey/text/linux-intro.tex.

In most Linux distributions, USB keys and CDs are automatically mounted when they are inserted or attached, and the default mount directory is a subdirectory of /media or /mnt. For example, your first CD-ROM drive might be mounted at /media/cdrom0, while the contents of a USB key might be accessible through /media/usb0. You may manually change the mount directory, but you will have to learn two shell commands and know the device file that represents your drive to do that (the one we talked about in the preceding section - disks also get their file representation in the /dev directory). We will cover this subject later.

Users

The user is a metaphor for somebody or something interacting with the system. Users are identified by a user name and a password. Internally, each user has a unique number assigned, which is called a user ID, or UID for short. You only need to know your UID in some rare situations. Users can additionally be organized in groups. There is one special user in all Linux systems, which has the user name "root" and UID 0. It is also called the superuser. The superuser can do anything and is not controlled in any way by the security mechanisms. Having such a user account is very useful for administrative tasks and configuring the system. In some distributions (like Ubuntu) direct access to the root account is disabled and other mechanisms are used instead.

If you have more than one user account on a Linux system, you do not need to log out and back again to switch impersonations. There are special shell commands that allow you to access files and execute programs as other users, provided you know their user names and passwords. Thanks to this mechanism, you can spend most of the time as a user with low-privileges and switch to a higher-privileged account only if you need to.

The advantage of running as a non-privileged user is that any mistakes you happen to make are very unlikely to damage the system. System-critical components can only be altered by the root user.

File permissions

Users exist to control the extent to which people and programs using the system can control it. This is accomplished by a system of file permissions. Each file belongs to one of the users - that is, each file has an owner. Additionally, a file can be assigned to a group of users, but the owner must be a member of that group. Each file has three kinds of permissions: read, write andexecute. These permissions can be assigned to three kinds of owner relations: owner, group and other. Other includes all users who are not the owner of the file and do not belong to the group which owns the file. Only the file owner or the superuser (root) can change the permissions or ownership of a file.

This system allows precise control over who can do what on a given computer. Users can be prevented from modifying system files by removing the "write" permission from them, or from executing certain commands by removing the "execute" permission. Notice that users may be allowed to execute programs but not alter them. This is very important, since most Linux systems include a compiler that allows you to create your own programs.

File permissions are usually given as three octal digits (each from 0 to 7). The digits represent the permissions for, respectively, owner, group and other users. Each digit is the sum of permission codes: 1 for execute, 2 for write and 4 for read. For example, "755" allows everyone to read or execute the file, but only its owner can write it. "400" allows the owner to read the file, and no one else is allowed to do anything. "540" allows the owner to read or execute the file, group members to only read the file and other users to do nothing.

chmod (change mode), chown (change owner), and chgrp (change group) are used to change file permissions.

SCL 2 : COMPUTER SOFTWARE

Question 2:

Discuss different types of threats and malicious program (malware) that can damage a computer, mobile devices or disrupt any system.

Search for information on current known malware program. Based on information that you have found, create a table to list different types of malware, what it does and how it can repaired or removed. These information is useful for you to prevent any malware from damage your computer system. 

Illustration of a Trojan horse

TROJAN HORSE

Trojan horse is defining as a malicious, security-breaking program that is disguised as something benign. For example, when you download what appear to be a music file from the internet but then you click on it, you unleash a program which do harmful things to your personal computer such as deleting your disk or letting someone to hijack your computer and commit crime from a remote location.

Computer viruses

Computer virus is programs that spreads malicious code by copying itself and infecting host computers and corrupt the computer system. Most viruses attached themselves to emails and media files such as CD, DVD and USB drivers that allow the virus to be downloaded when the files are opened.

Worms

Worms are similar to viruses which spread from computer to computer and disturb it. But unlike virus, worm can travel without any human action. Worms utilizes a computer network to send replicas of itself to connecting computes on that network.

ADWARE

Adware, also known advertising-supported software is any software application in which advertising banners are displayed while the program itself is running. Basically, the functions may be designed to analyze which Internet sites the user visits and to present advertising pertinent to the types of goods or services featured there. The term is sometimes used to refer to software that displays unwanted advertisements.

SPYWARE

Spyware is installed secretly on a computer system that collects and sends information about its usage and other confidential and personal data to the developer in an unethical manner. Basically, spyware is a tool that spammers use to attain personal information about users which is exploited and harvested without the user's consent and can be used to invade your privacy and compromise your personal data. They can collect personal information from your machine and also monitor your internet website viewing habits.

SUMMARIZATION ON TYPE OF MALWARE AND HOW CAN IT BE REPAIRED

Type of malware	What it does perform?	How it can be repaired or removed?
Computer viruses	To corrupt the computer system	Installing and running antivirus or antimalware programs
Worms	Worms utilizes a computer network to send replicas of itself to connecting computes on that network.	Using malware removing tools
Trojan horse	Trojan presented to the user as a form of a free useful software or add-on, once installed the Trojan gives access to hacker then carry out their criminal operations on the target computer from remote station.	It can removed either manually or using antivirus software program.
Spyware	It is installed secretly on a computer system that collects and sends information about its usage and other confidential and personal data to the developer in an unethical manner.	It can be repaired using antispyware tools.
Adware	The program is designed to display advertisements on a computer system.	Adware can be removed using trusted antispyware and antimalware software.

By:
Norazuwa Ramnor

Nurul Ain Zafirah Latif