TYPE OF BACKUP IN LINUX

INCREMENTAL BACKUP

An incremental backup is a type of backup that only copies files that have changed since the last backup. If a full backup was done on Monday, Tuesday's, incremental will backup files that have changed since Tuesday's incremental backup.

The main advantage of incremental backups is that fewer files are backed up daily, allowing for shorter backup windows. The disadvantages is that during a complete restore, the latest full and all subsequent incremental backups must be restored, which can take significantly longer.

DIFFERENTIAL BACKUP

A differential backup is a type of backup that copies all the data that's been changed since the last full backup. The size of a differential backup grows throughout the week and becomes progressively larger until the next full backup. A full restore from this type of backup only requires the last full backup and the last differential.

COMPARISON BETWEEN INCREMENTAL AND DIFFERENTIAL

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LINUX SHELLS

Shell is any interface through which a user can interact with the computer operating system.

TYPE OF SHELL

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COMMON FILE SYSTEM IN LINUX

File systems are one of the things any newcomer to Linux must become acquainted with. It is a file that organize the data and metadata on a storage device in computer.

EXT2

• This file system is the predecessor to the EXT3 file system.
• EXT2 is not journaled.
• Hence, it is not recommended any longer

EXT3

•  Most popular Linux file system, limited scalability in size and number of files.
• This file system journaled file system that has the greatest use in Linux.
• It is quite robust and quick, although it does not scale well large volumes nor great number of files.
• However, it is still not as scalable as some of the other file systems listed even with htrees.

FAT32

•  FAT32 is the crudest of the file systems listed.
• It is popular with its widespread use and in Windows desktop world. 
• It has made its way into being in the file system in flash RAM devices such as digital cameras, USB memory sticks and etc.
• It has no built in security access control, so is small and works well in these portable and embedded applications.
• It scales the least of the file systems listed and most systems have FAT32 compatibality due to its ubiquity.

GFS

•  The RedHat Global File System was open sourced in mid 2004.
• It is a parallel cluster file system which allows multiple machines to access common data on a SAN (Storage Area Network).
• This important for allowing multiple machines access to the same data to ease management such as common configuration files between multiple webservers.
• It also allows applications and services which are written to direct disk access to be scaled out to multiple nodes.

JFS

•  The IBM Journaled File System is the file system used by IBM in AIX and OS/2.
• It is a feature rich fie system ported to Linux to allow for ease of migration of existing data.
• It has been shown to provide excellent overall performance across a variety of workloads.

ReiserFS

•  The Reiser File System is the default file system in SUSE Linux distributions.
• It was designed to remove the scalability and performance limitations that exist in EXT2 and EXT3 file systems.
• It scales and performs extremely well on Linux, outscalling EXT3 with htrees.
• It is the best file system on Linux where there are a great number of small files in the file system.

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TYPE OF BOOT LOADERS IN LINUX

GRUB

• GNU GRUB short for GNU Grand Unified Bootloader.
• Reference implementation of the Multiboot Specification, which provides a user the choice to boot one of multiple operating system installed on a computer or select a specific kernel configuration available on a particular operating system's partitions 
• Features 
• - user can dynamically configure the GRUB sub-syste.
• - GRUB is highly portable and can be used in a variety of different user interfaces.
• - it can download operating-system images from a network and can support operating system that do not multi-boot.

LOADLIN

•  Loadlin is a Linux boot loader that runs under DOS or Microsoft Windows.
• Loadlin and the Linux kernel are both files on a file system accessible to DOS/Windows.
• It loads the Linux kernel into memory from a file. It also places various configuration parameters into memory and transfers control to the kernel. 
• The kernel reads these parameters, initializes and runs, replacing DOS/Windows completely.

 LILO

•  LILO was default boot loader for most Linux distributions in the years after the popularity of loadlin.
• LILO is a boot loader for Linux/x86 and other PC operating systems.
• It is responsible for loading your Linux kernel from either a floppy or a hard drive and passing control to it.
• It is capable of booting beyond cylinder 1024 of a hard disk if the BIOS supports EDD packet call extensions to the int 0x13 interface.
• LILO can also be used to boot many other operating systems, including DOS, Windows (all versions), OS/2, and the BSD variants
• The LILO distribution includes full source, documentation and support files.

SYSLINUX

• The Syslinux Project is suite of lightweight IBM PC MBR bootloaders for starting up computers with the Linux kernel.
• It normally used for booting full Linux installations since Linux is not normally on FAT file systems.
• Instead, it is often used for boot rescue floppy disks, USBs or other lightweight boot systems.
• Syslinux also presents a simple text interface that can be used to select between configurations defined in the configuration file and can be used to add parameters to the kernel.
  

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METHOD OF LINUX INSTALLATION

1. DVD/CD ROM

•  For this method, user need to have a DVD/CD ROM drive and the CD installation.
• User can download the official release Linux iso image from whatever distributions they choose from distribution's official website and burn it into cd or dvd.
• They also have many mirrors in regions around the world which provide cd and dvd iso image download using FTP or HTTP for faster download.

2. Hard Drive

• User need to transfer the set of Scientific Linux Installation CD iso images to adirectory on their hard drive. Be sure to do amd5sum on the iso's. It is to ensure the user downloaded properly.
•  Be usre to keep track of what drive, partition and directory on that you have your iso images. 

3. NFS (Network File System)

• If you need to install Linux on many machines, you can use NFS . It makes it easier and faster because it allows you to install Linux on your local network.
• However, you need to configure the NFS server in order to make it available to remote machines.

4. FTP

• You can use this method if you don't have Red Hat Linux CD-ROM or a CD-ROM drive but do have network access.
• When installing via FTP, the Red Hat Linux packages you select are downloaded (using FTP) across the network to your computer and are installed on your hard drive.

5.HTTP

•  Select this option if you have a HTTP (web) or FTP server that you can install from.
• If you have a web server running and want to enable HTTP access to your install server then add sym links from your document root to the install server directory and this will grant access.
• Then, make the install directory visible to your web server by making it appear under the document root by some means.

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REASONS TO MAKE PARTITION

Partitioning is the act of dividing a hard disk drive into multiple logical storage units referred to as partiotions, to treat one physical disk drive as if it were multiple disks. Partitions are also termed "slices" for operating systems based on BSD, Solaris or GNU Hurd. A partition editor software program can be used to create, resize, delete and manipulate these partitions on the hard disk.

There are some of the reasons to make partition.

• Easy to manage
  If you keep your operating system and applications on a partition separate from your data, the data will be more easier to back up and easier to restore. Its make your system more manageable. Another more, if you need to reinstall the operating system, you can do it without worrying about the data on the other partition.
   
• Backup and Recovery
  You can store a complete backup image (an exact clone/duplicate) of your whole Windows installation on a second partition. This can be used quickly restore Windows in the event of major problems without losing anything, so your settings, programs and Windows would be the same as at the time you created the backup. It also make it easier to recover a corrupted file system or operating system installation.


• Security
  Separation of the operating system files from user files may result into a better and secure system. Restrict the growth of certain file systems is possible using various techniques.
   
• Secure the data from virus / data crash
  Viruses and malware target files on the main Windows C: partition. If your document are stored there, they are much more likely to become infected than if they are stored in a separate D: partition. So if part of your hard drive becomes corrupted or infected with virus or malware, the other partitions have a good  chance of remaining unscathed.
   
•  Different file system
  By creating the partition and separate the system files and user files into a different file system, it may decrease the chance of corruption or accidental deletion of crucial system files.
  
  
• Multi Operating System
  For creating multiple operating system boots sequences. Different partitions can be used for different operating systems like Windows, Linux and other else.
   
• Squeeze more performance
  Partitioning a large drive into smaller units improves performance by decreasing the amount of traveling the drive's read/write head has to do when it searches for data. A partition also shrinks the size of the tables the computer uses to keep track of where dara is stored, further improving performance.
   
• Stability and Efficiency
  You can increase disk space efficiency by formatting disk with various block sizes. It depends upon the usage.

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KERNEL (MONOLITHIC KERNEL AND MICROKERNEL)

Kernel is a program that constitutes the central core of  a computer operating system. It has complete control over everything that occurs in the system. A kernel can be contrasted with a shell, which is the outermost part of an operating system and a program that interacts with user commands.

Monolithic

A monolithic kernel is an operating system architecture where the entire operating system is working in the kernel space and alone as supervisor mode. The monolithic differs from other operating system architectures (such as the microkernel architecture) in that it defines alone a high-level virtual interface over computer hardware, with a set of primitives or system calls to implement all operating system services such as process management, concurrency, and memory management itself and one or more device drivers as modules.

Properties of Monolithic Kernels

• OS is all in one place, below the “red line”

• Applications use a well-defined system call interface to interact with kernel

• Examples:  Unix, Windows NT/XP, Linux, BSD, OS/161

• Common in commercial systems

Advantages and disadvantage

Microkernel

Microkernel is the only software executing at the most privileged level (generally referred to as supervisor or kernel mode).[citation needed] Traditional operating system functions, such as device drivers, protocol stacks and file systems, are removed from the microkernel to run in user space.[citation needed] In source code size, microkernels tend to be under 10,000 lines of code, as a general rule. MINIX's kernel, for example has less than 6,000 lines of code.

 

Properties of Microkernels

• Design Philosophy:  protected kernel code provides minimal “small, clean, logical” set of abstractions

• Tasks and threads

• Virtual memory

• Interprocess communication

• Everything else is a server process running at user-level

• Examples: Mach, Chorus, QNX, GNU Hurd

• Mixed results

Microkernel Advantages and disadvantage

 

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BENEFITS OF USING LINUX

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. There are some benefits of using the Linux.

=> Flexibility

Linux can be used for high performance server applications, desktop applications and embendded systems. You can save disk space by only installing the components needed for a particular use. You can restrict the use of specific computers by installing for example only selected office applications instead of the whole suite.

=> Security
Linux is one of the most secure operating systems. "Walls" and the flexible file access permission systems prevent access by unwanted visitors or viruses. Linux users have to option to select and safely download software, free of charge, from online repositories containing thousands of high quality packages. No purchase transactions requiring credit card numbers or other sensitive personal information are necessary.

=> Reliability
The majority of Linux variant and versions are reliable, Can often run for months and years without needing to rebooted.

=> Scalability
Linux is to be very accommodative of increasing needs of servers. Its scalability along from its cost makes Linux a most profitable option.

=> Open Source licensing model (ROI)
When Linux came around, hardware vendors thought of it as the opportunity to reduce customers total cost of ownership. ROI is return on investment where gain from investment minus cost of investment divide overall cost of investment

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TYPES OF OPEN SOURCE SOFTWARE LICENSES

Masschusetts Institute of Technology (MIT)

• It is a free software license, means that is permits reuse within proprietary software provided all copies of the licensed software include of the MIT license term
• Originally developed at the Masschusetts Institute of Technology
• It is permissive license that allows the programmers to put the code in proprietary software on the condition that the license is given with that software
• It may refer to the"Expat License" or more accurately called the "X11 license" because it was first written for the X Window System
• It already published on official site at open source Initiative

General Public License (GPL)

•  It created by the Free Software Foundation (FSF) as licenses applicable to software that can be use freely
• Also called as General Public License (GNU) or Library General Public License (LGPL)
• It was originally written by Richard Stallman for the GNU project
• GPL is an application of the copyleft principles that derivative work must be distributed under the same terms as the original
• Any modification of to GPL licensed software must also be released under the GPL license
• Compared to GPL, LGPL applies a narrower interpretation of derivative works whereas is a modified version of the original source code

Berkeley Software Distribution (BSD)

• Are family of permissive free software licenses
• BSD was first written at the University of California, Berkeley for distributing a Unix-like operating system  and because of this, it make the original owners of the BSD were the Regents of the University of California
•  Because it has a few restrictions, it is often used by universities and the like for the products of research
• The license places minimal restrictions on how the software can be redistributed
• The first version of the license was revised and the resulting licenses are more properly called modified BSD licenses

Mozilla Public Licenses (MPL)

• MPL are developed and maintained by Mozilla Foundation
• This software license also created by Netscape for its open-source web browser
• It is characterized as a hybridization of the modified BSD license and GNU General Public License (GPL) that seeks to balance the concerns of proprietary and open source developers
• MPL has been approved as both a free software license by the Free Software Foundation (FSF) and an open-source software license by the Open Source Initiative
• Its allows covered source code to be mixed with other files under a different, even proprietary license
• If we modify source code that was published under this license, we are obliged to release it under the same license. However, if  we develop an original module as an addition to it, that restriction does not apply
• MPL is the license for the Mozilla Application suite, Mozilla Firefox, Mozilla Thunderbird and other Mozilla software but it has been used by such as Adobe to license their Flex product line

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OPEN SOURCE SOFTWARE LICENSES

An open-source software license is a statement that anyone is free to use your source code in whatever way they want.

 Open source rights:

* a user can create and distribute copies of the source code

* a user can obtain a program's source code

* a user can modify the source code

:) Academic

• Generally, academic software is stapled together in a tight deadline an expert user has to coerce it into running and it's not pretty code. 
• Academic code is about "proof of concept".
• Most open source licenses requires source and modifications to be shared with binaries and absolved author of legal liability.
• It should require that source and modifications used to validate scientific claims be released with those claims.
• Openness should also hinge on publication, once a paper is accepted, the licenses should force the release of modifications.

:) Community

•  Colleges and universities have used the term community source to refer to a type of community coordination mechanism that builds on the practices of open source communities.
• The software these collective efforts are distributed via an approved Open Source Initiative (OSI) license.
• Copyright of the software often is held by and independent foundation.
•  An important distinctive characteristic of community source as opposed to plain open source is that the community includes some organizations or institutions that are committing their resources to the community, in the form of human resources or other financial elements.
• In this way, the open source project will have both more solid support, rather than purely volunteer efforts as found in other open source communities and will possibly be shaped by the strategic requirements of the institution committing the resource.
  

:) Companies

• Open source software can be sold and use commercially.
• The use of dual-licensing provides an offer of the software under an open source license but also under a separate proprietary license term.
• With permissive software, any copany can distribute the package without the source or software freedoms.

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