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UNIT-4, Linux Operating System, Introduction to Linux Operating System:LINUX is an operating system or a kernel distributed under an open-source license. Linux is, a community of open-source Unix like operating systems that are based on the Linux Kernel., Its functionality list is quite like UNIX. The kernel is a program at the heart of the Linux, operating system that takes care of fundamental stuff, like letting hardware communicate, with software., It was initially released by Linus Torvalds on September 17, 1991. It is a free and opensource operating system and the source code can be modified and distributed to anyone, commercially or non commercially under the GNU General Public License., Initially, Linux was created for personal computers and gradually it was used in other, machines like servers, mainframe computers, supercomputers, etc. Nowadays, Linux is also, used in embedded systems like routers, automation controls, televisions, digital video, recorders, video game consoles, smart watches, etc. The biggest success of Linux is Android, (operating system) it is based on the Linux kernel that is running on smart phones and tablets., Files of Linux:- There are three file types of Linux. They are:Ordinary Files/Regular Files:- All files created by a user come under this category of files., These include all data files, program files, object files and executable files. A user can make, changes to such files., Directory Files:- For each directory there is a file by the same name as the directory, which, contains information about files under that directory. A directory files is automatically, created by Linux whenever a directory is created. A directory files contains two fields for, each file- the name of the file, and its identification number. A directory file cannot be, modified by a user but is instead, modified automatically by the system when a new file or a, sub-directory is added to the directory., Device Files:- Devices files are special files typically associated with input-output devices,, such as printers, hard-disks, floppy disks, CD-ROMs etc. The output directed to device file is, transmitted onto the respective physical device associated with the files name. The kernel is, responsible for mapping the file names to their respective devices.

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Directories of Linux:- The Linux directory structure is like a tree. The base of the Linux file, system hierarchy begins at the root. Directories branch off the root, but everything starts at, root. The following some of the important directories in Linux., , Figure: LINUX system directories, , (1) / (The Root Directory):- Everything on Linux system is located under the / directory,, known as the root directory. (The / directory as being similar to the C:\ directory on, Windows, but this isn’t strictly true, as Linux doesn’t have drive letters. While, another partition would be located at D:\ on Windows, this other partition would, appear in another folder under / on Linux)., (2) /bin:- This directory contains executable program files (binary files). In this directory,, one can find the files for the LINUX commands. It is similar to command.com files in, DOS., (3) /dev:- This directory contains the special device files. For example, the printer may be, a file known as prn in this directory, the hard disk may be had file and its first, partition would be hda0., (4) /etc:- This directory contains all the system-wide configuration information as text, files. The /etc directory contains configuration files, which can generally be edited by, hand in a text editor. User specific configuration files are located in each user’s home, directory., (5) /lib:- This directory contains the library files. Library files contain the reusable, functions and routines for the programmer to use., The /lib directory contains libraries needed by the essential binaries in the /bin, and /sbin folder. Libraries needed by the binaries in the /usr/bin folder are located in, /usr/lib., (6) /tmp:- This directory contains all the temporary files, which will eventually be, deleted from the system. Applications store temporary files in the /tmp directory., These files are generally deleted whenever the system is restarted and may be deleted, at any time by utilities such as tmpwatch. This is similar to the C:\windows\temp, directory in Windows-based OS.

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(7) /mnt:- This is the directory where the storage devices other than hard disks(floppy, disks and CD disks) are mounted. This directory contains the sub-directories “floppy”, and “cdrom”. When these devices are mounted, this directory shows the contents of, the floppy disk and CD-ROM respectively., (8) /usr:- This directory contains the home directories of the users, source text for the, online manual (man) pages, games and other directories. There is one home directory, for each user. For example, for a user called “mini”, these will be a directory with the, same name in usr directory. The directory mini will contain all the files and subdirectories created by the user “mini”., (9) /kernel():- This directory contains all the kernel-specific code. Kernel is the heart of, the LINUX system. It is responsible for resource-allocation, security and low-level, hardware-interface., , XX##XX