| Module | Unit | Topics | Links | Resources |
|---|---|---|---|---|
| 1 | 1.1 | Linux and its features | Open | |
| 1.2 | Linux History | Open | ||
| 1.3 | Linux OS internals | Open | ||
| 1.4 | Linux Distributions | Open | ||
| 2 | 2.1 | Process states in Linux | Open | |
| 3 | 3.1 | Linux Directories | Open | |
| 4 | 4.1 | Linux Basic Commands | Open | |
| 5 | 5.1 | Linux Networking | Open | |
| 5.2 | Apache2 Server Configuration | Open | ||
| 5.3 | NFS server Configuration | Open | ||
| 5.4 | Samba Server Configuartion | Open | ||
| 5.5 | FTP Server Configuration | Open | ||
| 6 | 6.1 | Shell Script | Open |
Linux is a Unix-like open-source computer operating system (OS) that directly manages hardware and resources of a system such as CPU, memory and storage and manages the communication between hardware and software. It was released on 5 October 1991 by Linus Torvalds and is considered more secure and faster. It is freely distributable and is generally built around Linux Kernel. Furthermore, it can be installed in mobiles, laptops, computers, notebooks, etc.
Today, supercomputers, smart phones, desktop, web servers, tablet, laptops and home appliances like washing machines, DVD players, routers, modems, cars, refrigerators, etc use Linux OS.
In earlier days, computers were as big as houses or parks. So you can imagine how difficult it was to operate them. Moreover, every computer has a different operating system which made it completely worse to operate on them. Every software was designed for a specific purpose and was unable to operate on other computer. It was extremely costly and normal people neither can afford it nor can understand it.
In 1969, a team of developers of Bell Labs started a project to make a common software for all the computers and named it as 'Unix'. It was simple and elegant, used 'C' language instead of assembly language and its code was recyclable. As it was recyclable, a part of its code now commonly called 'kernel' was used to develop the operating system and other functions and could be used on different systems. Also its source code was open source.
Initially, Unix was only found in large organizations like government, university, or larger financial corporations with mainframes and minicomputers (PC is a microcomputer).
In eighties, many organizations like IBM, HP and dozen other companies started creating their own Unix. It result in a mess of Unix dialects. Then in 1983, Richard Stallman developed GNU project with the goal to make it freely available Unix like operating system and to be used by everyone. But his project failed in gaining popularity. Many other Unix like operating system came into existence but none of them was able to gain popularity.
In 1991, Linus Torvalds a student at the university of Helsinki, Finland, thought to have a freely available academic version of Unix started writing its own code. Later this project became the Linux kernel. He wrote this program specially for his own PC as he wanted to use Unix 386 Intel computer but couldn't afford it. He did it on MINIX using GNU C compiler. GNU C compiler is still the main choice to compile Linux code but other compilers are also used like Intel C compiler.
He started it just for fun but ended up with such a large project. Firstly he wanted to name it as 'Freax' but later it became 'Linux'.
He published the Linux kernel under his own license and was restricted to use as commercially. Linux uses most of its tools from GNU software and are under GNU copyright. In 1992, he released the kernel under GNU General Public License.
- What are basic elements or components of Linux? Linux generally consists of five basic elements or components as given below:
Kernel: It is considered a core or main part of Linux and is generally responsible for all major activities of OS such as process management, device management, etc.
System Library: These are special functions or programs with the help of which application programs or system utilities can access features of the kernel without any requirement of code. It is simply used to implement the functionality of the OS.
System Utility: These are utility programs that are responsible to perform specialized and individual-level tasks. They are considered more liable and allow users to manage the computer.
Hardware: It is physical hardware that includes items such as a mouse, keyboard, display, CPU, etc.
Shell: It is an environment in which we can run our commands, shell scripts, and programs. It is an interface between user and kernel that hides all complexities of functions of the kernel from the user. It is used to execute commands.
There are on an average six hundred Linux distributors providing different features. Here, we'll discuss about some of the popular Linux distros today.
- Ubuntu It came into existence in 2004 by Canonical and quickly became popular. Canonical wants Ubuntu to be used as easy graphical Linux desktop without the use of command line. It is the most well known Linux distribution. Ubuntu is a next version of Debian and easy to use for newbies. It comes with a lots of pre-installed apps and easy to use repositories libraries.
Earlier, Ubuntu uses GNOME2 desktop environment but now it has developed its own unity desktop environment. It releases every six months and currently working to expand to run on tablets and smartphones.
- Linux Mint Mint is based on Ubuntu and uses its repository software so some packages are common in both.
Earlier it was an alternative of Ubuntu because media codecs and proprietary software are included in mint but was absent in Ubuntu. But now it has its own popularity and it uses cinnamon and mate desktop instead of Ubuntu's unity desktop environment.
- Debian Debian has its existence since 1993 and releases its versions much slowly then Ubuntu and mint.
This makes it one of the most stable Linux distributor.
Ubuntu is based on Debian and was founded to improve the core bits of Debian more quickly and make it more user friendly. Every release name of Debian is based on the name of the movie Toy Story.
- Red Hat Enterprise / CentOS Red hat is a commercial Linux distributor. There products are red hat enterprise Linux (RHEL) and Fedora which are freely available. RHEL is well tested before release and supported till seven years after the release, whereas, fedora provides faster update and without any support.
Red hat uses trademark law to prevent their software from being redistributed. CentOS is a community project that uses red hat enterprise Linux code but removes all its trademark and make it freely available. In other words, it is a free version of RHEL and provide a stable platform for a long time.
- Fedora It is a project that mainly focuses on free software and provides latest version of software. It doesn't make its own desktop environment but used 'upstream' software. By default it has GNOME3 desktop environment. It is less stable but provides the latest stuff.
The process, from its creation to completion, passes through various states. The minimum number of states is five.
The names of the states are not standardized although the process may be in one of the following states during execution.
-
New A program which is going to be picked up by the OS into the main memory is called a new process.
-
Ready Whenever a process is created, it directly enters in the ready state, in which, it waits for the CPU to be assigned. The OS picks the new processes from the secondary memory and put all of them in the main memory.
The processes which are ready for the execution and reside in the main memory are called ready state processes. There can be many processes present in the ready state.
-
Running One of the processes from the ready state will be chosen by the OS depending upon the scheduling algorithm. Hence, if we have only one CPU in our system, the number of running processes for a particular time will always be one. If we have n processors in the system then we can have n processes running simultaneously.
-
Block or wait From the Running state, a process can make the transition to the block or wait state depending upon the scheduling algorithm or the intrinsic behavior of the process.
When a process waits for a certain resource to be assigned or for the input from the user then the OS move this process to the block or wait state and assigns the CPU to the other processes.
-
Completion or termination When a process finishes its execution, it comes in the termination state. All the context of the process (Process Control Block) will also be deleted the process will be terminated by the Operating system.
-
Suspend ready A process in the ready state, which is moved to secondary memory from the main memory due to lack of the resources (mainly primary memory) is called in the suspend ready state.
If the main memory is full and a higher priority process comes for the execution then the OS have to make the room for the process in the main memory by throwing the lower priority process out into the secondary memory. The suspend ready processes remain in the secondary memory until the main memory gets available.
- Suspend wait Instead of removing the process from the ready queue, it's better to remove the blocked process which is waiting for some resources in the main memory. Since it is already waiting for some resource to get available hence it is better if it waits in the secondary memory and make room for the higher priority process. These processes complete their execution once the main memory gets available and their wait is finished.
-
Creation Once the process is created, it will be ready and come into the ready queue (main memory) and will be ready for the execution.
-
Scheduling Out of the many processes present in the ready queue, the Operating system chooses one process and start executing it. Selecting the process which is to be executed next, is known as scheduling.
-
Execution Once the process is scheduled for the execution, the processor starts executing it. Process may come to the blocked or wait state during the execution then in that case the processor starts executing the other processes.
-
Deletion/killing Once the purpose of the process gets over then the OS will kill the process. The Context of the process (PCB) will be deleted and the process gets terminated by the Operating system.
In Linux/Unix operating system everything is a file even directories are files, files are files, and devices like mouse, keyboard, printer, etc are also files. Here we are going to see the Directory Structure in Linux. Types of files in the Linux system.
General Files – It is also called ordinary files. It may be an image, video, program, or simple text files. These types of files can be in ASCII or Binary format. It is the most commonly used file in the Linux system.
- Directory Files – These types of files are a warehouse for other file types. It may be a directory file within a directory (subdirectory).
- Device Files – In a Windows-like operating system, devices like CD-ROM, and hard drives are represented as drive letters like F: G: H whereas in the Linux system device are represented as files. As for example, /dev/sda1, /dev/sda2 and so on.
We know that Windows-like operating system, files are stored in different folders on different data drives like C: D: E: whereas in the Linux/Unix operating system files are stored in a tree-like structure starting with the root directory as shown in the below diagram.
The base of the Linux/Unix file system hierarchy begins at the root and everything starts with the root directory. These are the common top-level directories associated with the root directory:
/bin – binary or executable programs. /etc – system configuration files. /home – home directory. It is the default current directory. /opt – optional or third-party software. /tmp – temporary space, typically cleared on reboot. /usr – User related programs. /var – log files.