DOC-20240821-WA0000..pdf

Ch.1 Introduction of Linux  Linux is an open-source operating system Like Windows, Mac, Android,Unix Unix and Linux commands are similar in nature What is operating system? An operating system is a software that enables communication between computer hardware and software. it co...

Ch.1 Introduction of Linux  Linux is an open-source operating system Like Windows, Mac, Android,Unix Unix and Linux commands are similar in nature What is operating system? An operating system is a software that enables communication between computer hardware and software. it conveys input to get processed by the processor and brings output to the hardware to display.  Types of system Single user Multi user Single user Single user Single user Single user single task multiple task Basic concept of multi user system A Multi-user operating system is a computer operating system which allows multiple users to access the single system with one operating system on it. the operating system should be capable of running multiple user programs. It uses the concept of scheduling There are two methods of scheduling: a) Time slice method b) Pre-emptive priority based scheduling  Terminal A Central Processor Terminal B Terminal C Components of Multi-User Operating System Memory-programs execution Kernel-interact with hardware(MM) CPU User interface Spooler-Simultaneous Peripheral Output on Line Features of the Multi-user Operating System 1. Multi-tasking 2. Resource sharing 3. Background processing Types of Multi-user Operating System 1. Distributed Systems: A distributed system contains multiple nodes that are physically separate but linked together using the network. All the nodes in this system communicate with each other and handle processes. Each of these nodes contains a small part of the distributed operating system software. Types of Distributed Systems 1. Client/Server Systems 2. Peer to Peer Systems 2. Time-sliced Systems: a short period is assigned to each task, i.e. each user is given a time slice of the CPU time. 3. Multiprocessor Systems: in this, the operating system utilises more than one processor. How to work the Multi-User operating system? The single master system is contained within the multi-user system. All network users can access the master system anytime and from any place and open their local version of the system. The local version is also known as a 'working model'. All users can update, delete, and create new files on their local working model, but this model will not be available to other users until it is saved to the master system. Characteristics of Multi-User Operating System 1.Resource Sharing Several devices, like printers, fax machines, plotters, and hard drives, can be shared in a multi-user operating system. Users can share their own documents using this functionality. All users are given a small slice of CPU time under this system. 2. Multi-Tasking Multi-user operating systems may execute several tasks simultaneously, and several programs may also execute at the same time. 3. Time-Sharing A strategy used by multi-user operating systems to operate on several user requests at the same time by switching between jobs at very short periods of time.  System The operating system must handle a computer's combination of hardware and software resources. Activity 1: Difference Between Single user and Multi user System  Single user Operating System Multi-user Operating System It is an operating system in which the user can manage one thing at a time It is an operating system in which multiple users can manage multiple effectively. resources at a time Example: MS DOS Example: Linux, Unix, windows 2000, windows 2003 etc. Single user Operating System has two types: Single user Single task Operating System and Single user Multi task Operating System. It is of three types: time-sharing operating system, distributed operating system and multiprocessor system. It is simple. It is complex. It provides a platform for one user at a time. It provides controlled access for the number of users by maintaining a database of known users. If another user wants to access the computer resources, then he/she has to wait There is no need to wait for accessing the computer resources. until the current process completes. This type of operating system is used for single user. This type of operating system is used for multiple users. Advantages of the Multi-user Operating System System efficiency. different users can access the same document on their computer. Disadvantages Private data sharing Virus Attack Characteristics of Linux OS 1.Multitasking 2.Multi user 3.Portability 4.Security 5. Communication 6. Graphical User Interface 7. Support's customized keyboard 8. File System 9. Open Source Linux provide 3 main security concepts Authentication: This simply implies claiming the person whom you are by assigning passwords and login names to individual users, ensuring that nobody can gain access to their work. Authorization: At the file level Linux has authorization limits to users, there are read, write and execute permissions for each file which decide who can access a particular file, who can modify it and who can execute it. Encryption: This feature encodes your files into an unreadable format that is also known as ‘cyphertext‘, so that even if someone succeeds in opening it your secrets will be safe. Structure Of Linux Operating System 1.Kernel 2. System Libraries 3. System Tools 4.Development tools 5.End User Tools Kernel kernel is the core of the operating system. It establishes communication between devices and software. it manages the system resources. it has four responsibilities: Middle Layer  Memory Management Device Kernel Management Process Management System Calls System Libraries System libraries are special programs that helps in accessing the kernel's features A kernel has to be triggered to perform a task and this triggering is done by the applications. Programmers have developed standard library of procedures to communicate with kernel. System Tools Linux OS has a set of utility tools which are usually simple commands With the help of command you can access your files, edit and manipulate data in your directories or files, change location of files or anything. Development Tools With the above three components your OS is running and working. But to update your system you have additional tools and libraries. End User Tools These end tools make a system unique for a user. Some example of end tools are graphic design tools, office suites, browsers, multimedia players, etc. Difference in unix and Linux Comparison Linux Unix Definition It is an open-source operating system which is freely It is an operating system which can be only used by its available to everyone. copyrighters. Example It has different distros like Ubuntu, Redhat, Fedora, IBM AIX, HP-UX and Sun Solaris. etc Users Nowadays, Linux is in great demand. Anyone can It was developed mainly for servers, workstations and use Linux whether a home user, developer or a mainframes. student. Usage Linux is used everywhere from servers, PC, It is used in servers, workstations and PCs. smartphones, tablets to mainframes and supercomputers. Cost Linux is freely distributed, downloaded, and Unix copyright vendors decide different costs for their distributed through magazines also. respective Unix Operating systems. Development As it is open source, it is developed by sharing and Unix was developed by AT&T Labs, various commercial collaboration of codes by world-wide developers. vendors and non-profit organizations. GUI Linux is command based but some Initially it was command based OS, distros provide GUI based Linux. but later Common Desktop Gnome and KDE are mostly used Environment was created. Most Unix GUI. distributions use Gnome. Interface The default interface is BASH It originally used Bourne shell. (Bourne Again SHell). But some distros have developed their own interfaces. File system support Linux supports more file system It also supports file system but than Unix. lesser than Linux Linux File System A file system is a logical collection of files on a partition or disk. is a layer which is under the operating system that handles the positioning of your data on the storage,  Ext: an old one and no longer used due to limitations. Ext2: first Linux file system that allows 2 terabytes of data allowed. Ext3: came from Ext2, but with upgrades and backward compatibility. The only problem about it that the servers don’t use this kind of file system because this file system doesn’t support file recovery or disk snapshots. Ext4: faster and allow large files with significant speed. XFS: old file system and works slowly Linux File System Directories /bin: Where Linux core commands reside like ls, mv. /boot: Where boot loader and boot files are located. /dev: Where all physical drives are mounted like USBs DVDs. /etc: Contains configurations for the installed packages. /home: Where every user will have a personal folder to put his folders with his name like /home/likegeeks. /lib: Where the libraries of the installed packages located since libraries shared among all packages /root: The home folder for the root user. /tmp: Contains the temporary files. /usr: Where the utilities and files shared between users on Linux. /var: Contains system logs and other variable data. Directory Structure uses a hierarchical file system structure root (/) at the base of the file system and all other directories spreading from there. Each file or directory is uniquely identified by its name, the directory in which it resides By convention, the root directory has an inode number of 2 and the lost+found directory has an inode number of 3. Inode numbers 0and 1 are not used. File inode numbers can be seen by specifying the -i option to ls command. Linux NIS The Linux NIS server (Network Information Service) is a server used for sharing critical data stored in files between systems on a network. it is used for storing user and group information that is traditionally stored in flat files like /etc/passwd. Virtual Memory Linux supports virtual memory, that is, using a disk as an extension of RAM The kernel will write the contents of a currently unused block of memory to the hard disk so that the memory can be used for another purpose When the original contents are needed again, they are read back into memory. It is termed as swap space  Shared Libraries Linux supports two classes of libraries, namely: Static libraries – are bound to a program statically at compile time. Dynamic or shared libraries – are loaded when a program is launched and loaded into memory and binding occurs at run time. Examples of libraries in Linux include libc (the standard C library) or glibc (GNU version of the standard C library), libcurl (multiprotocol file transfer library), libcrypt (library used for encryption, hashing, and encoding in C) CRON Schedular user can schedule and run tasks in the background automatically at regular intervals using Crontab command. Usedby system administrator you can automate process like backup, schedule updates and synchronization of files and many more. Each user can have their own crontab to create, modify and delete tasks By default cron is enable to users, however we can restrict adding entry in /etc/cron.deny file.  Crontab file consists of command per line and have six fields actually and separated either of space or tab. The beginning five fields represent time to run tasks and last field is for command. Minute (hold values between 0-59) Hour (hold values between 0-23) Day of Month (hold values between 1-31) Month of the year (hold values between 1-12 or Jan-Dec, you can use first three letters of each month’s name i.e Jan or Jun.) Day of week (hold values between 0-6 or Sun-Sat, Here also you can use first three letters of each day’s name i.e Sun or Wed. ) Command Advantages of Linux OS 1.Open Source 2.Security 3.Faster Software updates 4.Customization 5. Various Distributions 6. Free to use 7. Large Community Support: 8. Stability 9. Privacy 10. Performance: 11. Network Support 12. Compatibility 13. Fast and easy installation 14. Multitasking Evolution of Linux Linux is an operating system for personal computers developed by Linus Torvalds in 1991. Linux supported only the Intel 80x86 processor. Linux is one of very few operating systems that run on a wide range of processors, including Intel IA-32, Intel IA-64, AMD, DEC, PowerPC, Motorola, SPARC, and IBM S/390. Linux is similar to UNIX in that it borrows many ideas from UNIX and implements the UNIX API. It is used in areas such as embedded devices all the way to mainframes Structure of Linux OS The Linux Operating System’s architecture primarily has these components: the Kernel Hardware layer System library Shell System utility.  The kernel is the core part of the operating system, which is responsible for all the major activities of the LINUX operating system. This operating system consists of different modules and interacts directly with the underlying hardware. The kernel offers the required abstraction to hide application programs or low-level hardware details to the system. The types of Kernels are as follows: 1. Monolithic Kernel 2. Micro kernels 3. Exo kernels 4. Hybrid kernels 2. System libraries are special functions, that are used to implement the functionality of the operating system and do not require code access rights of kernel modules. 3. System Utility programs are liable to do individual, and specialized-level tasks. 4. Hardware layer of the LINUX operating system consists of peripheral devices such as RAM, HDD, CPU. 5. The shell is an interface between the user and the kernel, and it affords services of the kernel. It takes commands from the user and executes kernel’s functions. The Shell is present in different types of operating systems, which are classified into two types: command line shells graphical shells. Architecture  The architecture of a Linux System consists of the following layers − Hardware layer − Hardware consists of all peripheral devices (RAM/ HDD/ CPU etc). Kernel − It is the core component of Operating System, interacts directly with hardware, provides low level services to upper layer components. Shell − An interface to kernel, hiding complexity of kernel's functions from users. The shell takes commands from the user and executes kernel's functions. Utilities − Utility programs that provide the user most of the functionalities of an operating systems.