Yellowdog Updater Modified (YUM)

- It is an interactive program use to install,       remove, upgrade or query the packages.
- Added from RHEL 5 onward.
- It automatically computes dependences and figures out what thing should occur to install packages.
- It can be used to install from a local media, ftp server or nfs server.

  Installing package
[root@power_pc]# yum [option] <package 1>* <package 2>*

Options:

Install   installs the packages from the repository

update  updates the packages from the repository

remove removes the installed package

list        displays the packages in the repository

Linux Shell

Shell is an environment or a program for interacting with operating system. It is not a part of kernel, but uses the system kernel to execute programs.

-        A program that interprets commands.

-        Allows users to execute cmds by typing them manually at terminal, or automatically in programs called shell scripts.

-        A shell is not O. S. It is a way to interface with the O.S. And run commands.

Eg: sh, ksh, bash etc.

The bash:

-        bash stands for Bourne Again Shell.

-        Bash is a Unix shell written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell (sh). Bash is successor of 'sh'. So it has all of the features of original bourne shell , plus additionals that make it easier to program with and use from the command line.

-        Since it is free software, it has been adopted as the default shell on most of linux systems.

# file Globbing

#Tab key

history:

bash stores the history of commands that can be used to repeat if needed.

$history

-        displays the list of cmds history.

-        Arrow can be used to recall the commands.

-        Also;

!c         - to repeat the last command started with c.

!!          - to repeat the last command.

!n         - to repeat the command by its number.

Shell variables:

in linux shell there are two types of variables:

-       system variables:         created by linux developers(inbuilt)

                                         defined in upper case.

-      User Defined variables:           created by users.

 Defined in lower case.

Eg:       $echo $HOME

                 $echo $PATH

Getting help:

1)    $info <cmd>

eg $info ls

2)    $man <cmd>

eg: $man logout

The Culture of Free Software

The copyright of Fedora and Red Hat Enterprise Linux systems is covered under the GNU public license. That license, which most free software falls under, provides the following:

Author rights: The original author retains the rights to his or her software.

Free distribution: People can use the GNU software, changing and redistributing it as they please. They do, however, have to include the source code with their distribution (or make it easily available).

Copyright maintained: Even if you were to repackage and resell the software, the original GNU agreement must be maintained with the software. This means that all future receipients of the software must have the oppurtunity to change the source code, just as you did.

File System in linux

File System In computing, a file system  is used to control how data is stored and retrieved. Without a file system, information placed in a storage area would be one large body of data with no way to tell where one piece of information stops and the next begins. By separating the data into individual pieces, and giving each piece a name, the information is easily separated and identified. Taking its name from the way paper-based information systems are named, each group of data is called a "file". The structure and logic rules used to manage the groups of information and their names is called a "file system".

There are many different kinds of file systems.

FAT (File Allocation Table): The family of FAT file systems is supported by almost all operating systems for personal computers, including all versions of Windows and MS-DOS. The FAT file system traces its roots back to an (incompatible) 8-bit FAT precursor. Over the years, the file system has been expanded from FAT12 to FAT16 and FAT32. Various features have been added to the file system including subdirectories, codepage support, extended attributes, and long filenames.

The FAT12 and FAT16 file systems had a limit on the number of entries in the root directory of the file system and had restrictions on the maximum size of FAT-formatted disks or partitions.

FAT32 addresses the limitations in FAT12 and FAT16, except for the file size limit of close to 4 GB, but it remains limited compared to NTFS. FAT12, FAT16 and FAT32 also have a limit of eight characters for the file name, and three characters for the extension (such as .exe). This is commonly referred to as the 8.3 filename limit.

NTFS (New Technology File System):

NTFS is a proprietary file system developed by Microsoft.  Starting with Windows NT 3.1, it is the default file system of Windows NT family.

NTFS has several technical improvements over FAT and HPFS (High Performance File System), the file systems that it superseded, such as improved support for metadata, and the use of advanced data structures to improve performance, reliability, and disk space utilization, plus additional extensions, such as security access control lists (ACL)

EXT(Extended File System):

The extended file system, or ext, was implemented in April 1992 as the first file system created specifically for the Linux kernel. It has metadata structure inspired by the traditional Unix File System (UFS) and was designed by Rémy Card to overcome certain limitations of the MINIX file system. It could handle file systems up to 2 gigabytes (GB) in size.

ext was the first in the series of extended file systems. It was immediately superseded by both ext2 and xiafs, which competed for a time, but ext2 won because of its long-term viability: ext2 remedied issues with ext, such as the immutability of inodes and fragmentation.

Features of Linux

Multiuser: Multiple users can log in and work on the system at the same time. Each users can have their own home directory for storing files and their own desktop interface. User accounts can be password protected, so that users can control who has access to their application and data.

Multitasking: In Linux it is possible to run many programs at the same time. Linux have many programs running at the background. Many of these processes make it possible for Linux to work as server, with these background processes listening to the network for requests to log in to your system, view a web page, print a document or copy a file. These background processes are referred to as daemons.

Hardware Support: You can configure support for almost every type of hardware device. There is support for floppy disk drives, CD-ROM’s, removable disks, sound cards, tape drives, video cards etc. Linux needs a driver, a piece of software that interfaces between the Linux kernel and the device.

Networking Connectivity: Linux offers support for variety of LAN cards, modems, serial devices. In addition to LAN protocols, all upper level protocols can be built-in. The most popular of these is TCP/IP but other protocols like IPX and X.25 are also available.

Network Servers: Providing networking services to the client computers is what Linux does best. A variety of software packages are available that enable you to use Linux as a print server, file server, FTP server, mail server, web server, news server,or workgroup (DHCP or NIS) server

Disadvantages of Linux

Many Windows programs will not run in Linux:  iTunes, Microsoft Office, Internet Explorer and many other Windows programs will not run natively in Linux.

There is a smaller selection of peripheral hardware drivers for Linux:  There is a smaller selection of peripheral hardware drivers (for printers, scanners, and other devices) in Linux as compared to Windows, though many new Linux hardware drivers are constantly being added.

There is a learning curve for people who are new to Linux:  Despite this, most Linux distros, especially the major ones, are very intuitive and user-friendly. Also, the desktop environments in Linux are in many ways similar to Windows in their appearance. One thing which should be emphasized is that there is also a learning curve for Windows XP users who switch to Windows 7 or Windows 8.

Advantages of Linux

Freedom:  Most Linux distros are free..... users do not need to pay for a copy, but this is only one aspect of freedom enjoyed by Linux users! In addition, Linux distros can be freely downloaded and legally installed on as many computers as you want and freely (and legally) given to other people. Because most distros are open source, you have access to the source code and can customize Linux to be whatever you want it to be; you can even create your own distro if you like!

Linux is easy to install:  In many instances, it is actually easier to install Linux to your computer than Windows.

Linux is very stable:  Linux systems rarely crash, and when they do, the whole system normally does not go down. The "blue screen of death" familiar to Windows users is not a worry for Linux users.

Linux is less vulnerable to computer malware:  Because most computer malware are designed to attack Windows (often through Active X which is not typically found in Linux) the odds are considerably less for Linux to be infected with a virus than Windows

Linux typically does not slow down over time: Unlike Windows, Linux does not easily become bogged down with spyware, viruses, trojans, etc., which can greatly reduce a computer's performance. Also, because Linux does not have a registry like Windows, it is not plagued with registry errors which can slow down a computer over time. Finally, the hard drives on Windows (especially Windows XP and older) computers need to be defragmented on a regular basis in order to maintain faster performance, due to being formatted in NTFS. On the other hand, because Linux is normally formatted in a different way using ext4 among others, there is no need to defragment a Linux hard drive.

Linux can breathe new life into old computers:  If you have an older computer (especially Pentium III or later) laying around, you can install Linux and in essence have a new computer. In many cases Linux will run faster and you can do all of the basics such as browse the Internet, email, play games, and create and edit documents, spreadsheets, and PowerPoint presentations. It should also be mentioned that Linux runs great on newer computers as well.

With Linux, you have so many choices in a wide variety of distros:  Linux comes in all sizes and flavors, which offers a wide variety from which to choose the distro which will best suit your needs. Another advantage of this variety is the innovation that is taking place in the Linux world because it is open source.

With many Linux distros, you have access to free software which numbers in the thousands!  Popular distros such as Ubuntu, PCLinuxOS, and OpenSUSE offer excellent software repositories within their package managers where virtually any type of software can be downloaded and installed to your Linux system for free.

what is Shell?

Shell In computing, a shell is a user interface for access to an operating system's services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation.

Shell program in Window: cmd

Shell programs in Linux: bash, ksh, tcsh and zsh.

What is Kernel?

Kernel In computing, the kernel is a computer program that manages input/output requests from software, and translates them into data processing instructions for the central processing unit and other electronic components of a computer. The kernel is a fundamental part of a modern computer's operating system.

History of Linux

When Linus Torvalds was studying at the University of Helsinki, he was using a version of the UNIX operating system called 'Minix'. Linus and other users sent requests for modifications and improvements to Minix's creator, Andrew Tanenbaum, but he felt that they weren't necessary. That's when Linus decided to create his own operating system that would take into account users' comments and suggestions for improvements.

This philosophy of asking for users' comments and suggestions and using them to improve computer programs was not new. Richard Stallman, who worked at the Massachusetts Institute of Technology, had been advocating just such an approach to computer programming and use since the early 1970's. He was a pioneer in the concept of 'free software', always pointing out that 'free' means 'freedom', not zero cost. Finding it difficult to continue working under conditions that he felt went against his concept of 'free software' he left MIT in 1984 and founded GNU. The goal of GNU was to produce software that was free to use, distribute and modify. Linus Torvalds' goal 6 years later was basically the same: to produce an operating system that took into account user feedback.

In 1991, ideal conditions existed that would create Linux. In essence, Linus Torvalds had a kernel but no programs of his own, Richard Stallman and GNU had programs but no working kernel.

Late in 1991, Linus Torvalds had his kernel and a few GNU programs wrapped around it so it would work well enough to show other people what he had done. And that's what he did. The first people to see Linux knew that Linus was on to something. At this point, though, he needed more people to help him.

People all over the world decided to take him up on it. At first, only people with extensive computer programming knowledge would be able to do anything with that early public version of Linux. These people started to offer their help. The version numbers of Linux were getting higher and higher. People began writing programs specifically to be run under Linux. Developers began writing drivers for different video cards, sound cards and other gadgets inside and outside your computer could use Linux. 

What is Linux?

Linux is an operating system that evolved from a kernel created by Linus Torvalds when he was a student at the University of Helsinki.

To say that Linux is an operating system means that it's meant to be used as an alternative to other operating systems, Windows, Mac OS, MS-DOS, Solaris and others.

 Linux is not a program like a word processor and is not a set of programs like an office suite. Linux is an interface between computer/server hardware, and the programs which run on it.