Commercial Linux vs Open Source Linux

Commercial Linux 

Many people might have no idea about Commercial Linux Distribution. Some think that it is like Microsoft or Apple. NO but it is different, Commercial Linux Distribution is free to use but if you want their support you need to pay.

Best example for Commercial Linux is Redhat Linux, it is free to use it, But if you need their support you have to pay for it.

There are million of companies use linux in their server system and also many educational institute use linux based server. 

These  Server system are difficult to configure for a individual so for that purpose there is Commercial linux Distribution.

If you are using Commercial linux Distribution for free and if you stuck with any problem in the linux Distribution you can subscribe it and take their help. 

CentOS / Red Hat Enterprise Linux

Red Hat Enterprise Linux is a commercial Linux distribution intended for servers and workstations. It’s based on the open-source Fedora project, but is designed to be a stable platform with long-term support.

Red Hat uses trademark law to prevent their official Red Hat Enterprise Linux software from being redistributed. However, the core software is free and open-source. CentOS is a community project that takes the Red Hat Enterprise Linux code, removes all Red Hat’s trademarks, and makes it available for free use and distribution. It’s a free version of RHEL, so it’s good if you want a stable platform that will be supported for a long time. CentOS and Red Hat recently announced they’re collaborating, so CentOS is now part of Red Hat itself.

Open Source Linux

Ubuntu

Ubuntu is probably the most well-known Linux distribution. Ubuntu is based on Debian, but it has its own software repositories. Much of the software in these repositories is synced from Debian’s repositories.

The Ubuntu project has a focus on providing a solid desktop (and server) experience, and it isn’t afraid to build its own custom technology to do it. Ubuntu used to use the GNOME 2 desktop environment, but it now uses its own Unity desktop environment. Ubuntu is even building its own Mir graphical server while other distributions are working on the Wayland.

Ubuntu is modern without being too bleeding edge. It offers releases every six months, with a more stable LTS (long term support) release every two years. Ubuntu is currently working on expanding the Ubuntu distribution to run on smartphones and tablets.

Linux Mint

Mint is a Linux distribution built on top of Ubuntu. It uses Ubuntu’s software repositories, so the same packages are available on both. Originally Mint was an alternative distribution loved mainly because it included media codecs and proprietary software that Ubuntu didn’t include by default.

This distribution now has its own identity. You won’t find Ubuntu’s own Unity desktop here — instead, you get a more traditional Cinnamon or MATE desktop. Mint takes a more relaxed approach to software updates and won’t automatically install critical software updates. Controversially, this has led some Ubuntu developers to label it insecure.

Debian

Debian is an operating system composed only of free, open-source software. The Debian project has been operating since 1993 — over 20 years ago! This widely respected project is still releasing new versions of Debian, but it’s known for moving much more slowly than distributions like Ubuntu or Linux Mint. This can make it more stable and conservative, which is ideal for some systems.

Ubuntu was originally founded to take the core bits of stable Debian and improve on them more quickly, packaging the software together into a user-friendly system that’s more frequently updated.

Fedora

Fedora is a project with a strong focus on free software — you won’t find an easy way to install proprietary graphics drivers here, although third-party repositories are available. Fedora is bleeding edge and contains the latest versions of software.

Unlike Ubuntu, Fedora doesn’t make its own desktop environment or other software. Instead, the Fedora project uses “upstream” software, providing a platform that integrates all this upstream software without adding their own custom tools or patching it too much. Fedora comes with the GNOME 3 desktop environment by default, although you can also get “spins” that come with other desktop environments.

Fedora is sponsored by Red Hat, and is the foundation for the commercial Red Hat Enterprise Linux project. Unlike RHEL, Fedora is bleeding edge and not supported for long. If you want a more stable release that’s supported for longer, Red Hat would prefer you use their Enterprise product.

openSUSE / SUSE Linux Enterprise

openSUSE is a community-created Linux distribution sponsored by Novell. Novell purchased SuSE Linux in 2003, and they still create an enterprise Linux project known as SUSE Linux Enterprise. Where Red Hat has the Fedora project that feeds into Red Hat Enterprise Linux, Novell has the openSUSE project that feeds into SUSE Linux Enterprise.

Like Fedora, openSUSE is a more bleeding edge version of Linux. SUSE was once one of the great user-friendly desktop Linux distributions, but Ubuntu eventually took that crown.

Mageia / Mandriva

Mageia is a fork of Mandriva Linux created in 2011. Mandriva — known as Mandrake before that — was once one of the great user-friendly Linux distributions.

Like Fedora and openSUSE, this is a community-created project to create an open-source Linux distribution. Mandriva SA no longer creates a consumer Linux distribution for desktop PCs, but their business Linux server projects are based on Mageia code — just like how Fedora and openSUSE provide code to their enterprise equivalents.

Arch Linux

Arch Linux is more old school than many of the other Linux distributions here. It’s designed to be flexible, lightweight, minimal, and to “Keep it Simple.” Keeping it simple doesn’t mean Arch provides tons of graphical utilities and automatic configuration scripts to help you set up your system. Instead, it means Arch dispenses with that stuff and gets out of your way.

You’re in charge of configuring your system properly and installing the software you like. Arch doesn’t provide an official graphical interface for its package manager or complex graphical configuration tools. Instead, it provides clean configuration files designed for easy editing. The installation disc dumps you at a terminal, where you’ll need to enter the appropriate commands to configure your system, partition your disks, and install the operating system yourself.

Arch uses a “rolling release” model, which means any installation image is just a snapshot of the current software. Every bit of software will be updated over time without you needing to upgrade to a new “release” of Arch.

This distribution has a bit in common with Gentoo, which was popular at one time. Both Linux distributions are designed for users who know how their systems work or who are at least willing to learn. However, Arch uses binary packages while Gentoo had an (unnecessary) focus on compiling every bit of software from source — this means it’s quick to install software on Arch as you don’t have to spend CPU cycles and time waiting for software to compile.

Slackware Linux

Slackware is another institution. Founded in 1993, Slackware is the oldest Linux distribution that’s still maintained and putting out new releases today.

Its pedigree shows — like Arch, Slackware dispenses with all those unnecessary graphical tools and automatic configuration scripts. There’s no graphical installation procedure — you’ll have to partition your disk manually and then run the setup program. Slackware boots to a command-line environment by default. It’s a very conservative Linux distribution.

Puppy Linux

Puppy Linux is another fairly well-known Linux  distribution. Previous versions have been built 

on Ubuntu, but the latest is built on Slackware. Puppy is designed to be a small, lightweight operating system that can run well on very old computers. The puppy ISO file is 161 MB, and Puppy can boot from that disc in a live environment. Puppy can run on PCs with 256 MB or RAM, although it does recommend 512 MB for the best experience.

Puppy isn’t the most modern and doesn’t have all the flashiest bells and whistles, but it can help you revive an old PC.

These aren’t the only Linux distributions out there.  Distrowatch lists many and tries to rank them by popularity.

                      The choice is yours 

Linux Boot Process

1.BIOS(Basic Input/Output System)
        2.MBR(Master Boot Record)
        3.LILO or GRUB
            LILO:-LInux LOader
            GRUB:-GRand Unified Bootloader
        4.Kernel
        5.init
       6.Run Levels
1.BIOS:
     i.When we power on BIOS performs a Power-On Self-Test (POST) for all of the different hardware components in the system to make sure everything is working properly
     ii.Also it checks for whether the computer is being started from an off position (cold boot) or from a restart (warm boot) is
stored at this location.
     iii.Retrieves information from CMOS (Complementary Metal-Oxide Semiconductor) a battery operated memory chip on the motherboard that stores time, date, and critical system information.
     iv.Once BIOS sees everything is fine it will begin searching for an operating system Boot Sector on a valid master boot sector
on all available drives like hard disks,CD-ROM drive etc.
     v.Once BIOS finds a valid MBR it will give the instructions to boot and executes the first 512-byte boot sector that is the first
sector (“Sector 0″) of a partitioned data storage device such as hard disk or CD-ROM etc .
2.MBR
     i. Normally we use multi-level boot loader.Here MBR means I am referencing to DOS MBR.
     ii.Afer BIOS executes a valid DOS MBR,the DOS MBR will search for a valid primary partition marked as bootable on the hard disk.
     iii.If MBR finds a valid bootable primary partition then it executes the first 512-bytes of that partition which is second level MBR.
     iv. In linux we have two types of the above mentioned second level MBR known as LILO and GRUB
3.LILO
     i.LILO is a linux boot loader which is too big to fit into single sector of 512-bytes.
    It is divided into two parts :an installer and a runtime module.
     iii.The installer module places the runtime module on MBR.The runtime module has the info about all operating systems installed.
     iv.When the runtime module is executed it selects the operating system to load and transfers the control to kernel.
     v.LILO does not understand filesystems and boot images to be loaded and treats them as raw disk offsets
GRUB
     i.GRUB MBR consists of 446 bytes of primary bootloader code and 64 bytes of the partition table.
     ii.GRUB locates all the operating systems installed and gives a GUI to select the operating system need to be loaded.
     iii.Once user selects the operating system GRUB will pass control to the karnel of that operating system.
See below what is the difference between LILO and GRUBThe original file is /etc/grub.conf of which you can observe a symlink file at /boot/grub/grub.conf

Sample /boot/grub/grub.conf
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux Server (2.6.18-194.26.1.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-194.26.1.el5 ro root=/dev/VolGroup00/root clocksource=acpi_pm divisor=10
        initrd /initrd-2.6.18-194.26.1.el5.img
title Red Hat Enterprise Linux Server (2.6.18-194.11.4.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-194.11.4.el5 ro root=/dev/VolGroup00/root clocksource=acpi_pm divisor=10
        initrd /initrd-2.6.18-194.11.4.el5.img
title Red Hat Enterprise Linux Server (2.6.18-194.11.3.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-194.11.3.el5 ro root=/dev/VolGroup00/root clocksource=acpi_pm divisor=10
        initrd /initrd-2.6.18-194.11.3.el5.img

4.Kernel
     i.Once GRUB or LILO transfers the control to Kernel,the Kernels does the following tasks

• Intitialises devices and loads initrd module
• mounts root filesystem

5.Init
     i.The kernel, once it is loaded, finds init in sbin(/sbin/init) and executes it.
     ii.Hence the first process which is started in linux is init process.
     iii.This init process reads /etc/inittab file and sets the path, starts swapping, checks the file systems, and so on.
     

• Executes the system to boot into the run level as specified in /etc/inittab

Sample output defining the default boot runlevel inside /etc/inittab
# Default runlevel. The runlevels used by RHS are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode
#   4 - unused
#   5 - X11
#   6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:6.Runlevel
     i.There are 7 run levels in which the linux OS runs and different run levels serves for different purpose.The descriptions are
given below.

• 0  – halt
• 1  – Single user mode
• 2  – Multiuser, without NFS (The same as 3, if you don’t have networking)
• 3  – Full multiuser mode
• 4  – unused
• 5  – X11
• 6  – Reboot

     ii.We can set in which runlevel we want to run our operating system by defining it on /etc/inittab file.

Below are given some few  important differences about LILO and GRUB

LILO	GRUB
LILO has no interactive command interface	GRUB has interactive command interface
LILO does not support booting from a network	GRUB does support booting from a network
If you change your LILO config file, you have to rewrite the LILO stage one boot loader to the MBR	GRUB automatically detects any change in config file and auto loads the OS
LILO supports only linux operating system	GRUB supports large number of OS

Linux vs Windows vs Mac OS

Linux vs Macintosh vs Windows (unbiased comparison)In this article, I will be outlining the pros and cons of the three major operating systems: Linux, Mac and Windows (commonly referred to as "PC"). Keep in mind that there are many other operating systems, but I will not be reviewing them because of their very small market share.

Let's start with the most popular: Windows

With almost 90% of the operating system market share, you can't miss Windows. It's in commercial buildings, industrial facilities, as well as home computers. Windows, having been introduced in 1985, is a very mature and complete piece of software. Yet, it has it's flaws... Pros: 

1. Compatibility: Almost every application, driver or game will work on Windows.

1. Technical support: Having so many users, you can always find someone (either online or offline) who can help you with Windows.

1. Huge quantity of function: When you get to know Windows well, you'll find out that there are so many functions that you can do almost anything quite easily.

Cons:

1. Viruses: You may need to buy an antivirus program, although free ones exist.

1. Slow: Windows, especially Vista and 7, requires a lot of computer resources (memory, processor, disk space), and thus, runs slower.

1. Price: It easily costs over a hundred dollars.

Another big player: Macintosh

Apple's Macintosh OS is even older than Windows. It is the first ever successful graphical-based operating system, being released one year before it's Microsoft counterpart. Pros:

1. Viruses: Apple Macs get almost no viruses. This is mostly due to Window's superior market share.

1. Reliability: Macs only run on Apple computers, and are thus less prone to hardware and software crashing.

1. Looks: Let's face it, most of the time, Mac just looks better than Windows.

Cons: 

1. Expensive: Mac costs even more than Windows.

1. Only available on Apple computers: If you already have a computer, you cannot install MAC on it unless it's an Apple. Otherwise, you must buy a new computer.

1. Compatibility: Only a few programs will run on Mac, and almost no games.

Smaller but growing: LinuxLinux is GNU's answer to Mac and Windows. Yes, this means that Linux is FREE! By free, you can download, modify and redistribute it without spending a dime! . Linux is a younger player in the OS world, having been written in 1991, and is optimized for modern use (well, more than Windows and Mac). Unfortunately, it has some disadvantages also...Pros:

1. Price: Linux is F-R-E-E. You can download it, install it, use it, modify it... All for a whooping 0$.

1. Variety: Linux is not a full operating system. It is just a kernel. To use the kernel, additional software needs to be bundled with Linux. Several hundreds of these bundles (called "distributions" or simply "distros") exist. The most popular ones include Ubuntu, Mint and Fedora. The good thing is, with so many different flavours of Linux, there is always one to suit your needs!

1. Viruses: Although being more vulnerable to viruses than Mac (because it is open source), Linux still has very, very, very few viruses.

Cons:

1. Complicated: Although some distros are quite easy to use, most of them will required a good deal of computer knowledge in order to get them to work. 

1. Compatibility: Like Mac, representing only a few percents of the market share, Linux does not have as many programs and games as Windows.

1. Vendors: You won't find a lot of vendors selling Linux computers. Usually, you'll just end up having to buy Windows computer, reformatting the hard drive, and installing Linux yourself.

Bottom lineNo operating system is really better, the choice is up to you. If you're a gamer, then you have no choice, go for Windows. Programmers might prefer Linux and video/graphics producers will probably tend towards Mac. The best thing to do is probably to try each OS and see which is best for you!

Linux Filesystems Explained

Introduction to File systems:
File systems are one of the things any newcomer to linux must become acquainted with. In the world of Microsoft you never really have to worry about it, the default being NTFS. Linux however, being built on a world of open source and differing opinions, is not limited in this way and so the user should have an understanding of what a file system is, and how it affects the computer.
At the core of a computer, it's all 1s and 0s, but the organization of that data is not quite as simple. A bit is a 1 or a 0, a byte is composed of 8 bits, a kibibyte is 1024 (i.e. 2^10) bytes, a mebibyte is 1024 kibibytes and so on and so forth. All these bits and bytes are permanently stored on a Hard Drive. A hard drive stores all your data, any time you save a file, you're writing thousands of 1s and 0s to a metallic disc, changing the magnetic properties that can later be read as 1 or 0. There is so much data on a hard drive that there has to be some way to organize it, like a library of books and the old card drawers that indexed all of them, without that index, we'd be lost. Libraries, for the most part, use the Dewey Decimal System to organize their books, but there exist other systems to do so, none of which have attained the same fame as Mr. Dewey's invention. File systems are the same way. The ones most users are aware of are the ones Windows uses, the vFat or the NTFS systems, these are the Windows default file systems.
There are several different attributes which are necessary in defining file systems, these include their max file size, max partition size, whether they journal or not.

Journaling:
A journaling file system is more reliable when it comes to data storage. Journaling file systems do not necessarily prevent corruption, but they do prevent inconsistency and are much faster at file system checks than non-journaled file systems. If a power failure happens while you are saving a file, the save will not complete and you end up with corrupted data and an inconsistent file system. Instead of actually writing directly to the part of the disk where the file is stored, a journaling file system first writes it to another part of the hard drive and notes the necessary changes to a log, then in the background it goes through each entry to the journal and begins to complete the task, and when the task is complete, it checks it off on the list. Thus the file system is always in a consistent state (the file got saved, the journal reports it as not completely saved, or the journal is inconsistent (but can be rebuilt from the file system)). Some journaling file systems can prevent corruption as well by writing data twice.
Table
Now below is a very brief comparison of the most common file systems in use with the Linux world.

File System	Max File Size	Max Partition Size	Journaling	Notes
Fat16	2 GiB	2 GiB	No	Legacy
Fat32	4 GiB	8 TiB	No	Legacy
NTFS	2 TiB	256 TiB	Yes	(For Windows Compatibility) NTFS-3g is installed by default in Ubuntu, allowing Read/Write support
ext2	2 TiB	32 TiB	No	Legacy
ext3	2 TiB	32 TiB	Yes	Standard linux filesystem for many years. Best choice for super-standard installation.
ext4	16 TiB	1 EiB	Yes	Modern iteration of ext3. Best choice for new installations where super-standard isn't necessary.
reiserFS	8 TiB	16 TiB	Yes	No longer well-maintained.
JFS	4PiB	32PiB	Yes (metadata)	Created by IBM - Not well maintained.
XFS	8 EiB	8 EiB	Yes (metadata)	Created by SGI. Best choice for a mix of stability and advanced journaling.
GiB = Gibibyte (1024 MiB) :: TiB = Tebibyte (1024 GiB) :: PiB = Pebibyte (1024 TiB) :: EiB = Exbibyte (1024 PiB)

Above you'll see a brief comparison of two main attributes of different filesystems, the max file size and the largest a partition of that data can be.
Of the above file systems the only one you cannot install Linux on is the NTFS. It is not recommended to install Linux on any type of FAT file system, because FAT does not have any of the permissions of a true Unix FS.

Editing Files:
Those used to a Windows file system (NTFS, FAT) know that it isn't normally possible to change files while they are open. This restriction does not exist in a Unix file system. This is because in Unix file systems, files are indexed by a number, called the inode, and each inode has several attributes associated with it, like permissions, name, etc. When you delete a file, what really happens is the inode is unlinked from the filename, but if some other program is using the file, it still has a link open to the OS, and will continue to be updated. A file is not really deleted until all links have been removed (even then, the data is still on the disk, but not indexed in anyway and thus very hard to recover). All of this means that you can delete executing programs while they're running without crashing and move files before they're finished downloading without corruption.

Fragmentation:
Another common Windows practice that is not needed in Unix is defragmenting the hard drive. When NTFS and FAT write files to the hard drive, they don't always keep pieces (known as blocks) of files together. Therefore, to maintain the performance of the computer, the hard drive needs to be "defragged" every once in a while. This is unnecessary on Unix File systems due to the way it was designed. When ext3 was developed, it was coded so that it would keep blocks of files together or at least near each other.
No true defragmenting tools exist for the ext3 file system, but tools for defragmenting will be included with the ext4 file system.

In what ways Linux Filesystem is different from Windows Filesystem

What is a file system?

Any computer file is stored on some kind of a storage with a given capacity. Actually, each storage is a linear space for reading or both reading and writing digital information. Each byte of information on the storage has its own offset from the storage start (address) and is referenced by this address. A storage can be presented as a grid with a set of numbered cells (each cell is a single byte). Any file saved to the storage gets a number of these cells.

Generally, computer storages use a pair of sector and in-sector offset to reference any byte of information on the storage. The sector is a group of bytes (usually 512 bytes) that is a minimum addressable unit of the physical storage. For example, byte 1040 on a hard disk will be referenced as a sector #3 and offset in sector 16 bytes ([sector]+[sector]+[16 bytes]). This scheme is applied to optimize storage addressing and use a smaller number to reference any portion of information on the storage.

To omit the second part of the address (in-sector offset), files storing begins in the sector start and occupy the whole sectors (e.g.: 10-byte file occupies the whole sector, 512-byte file also occupies the whole sector, at the same time, 514 byte file occupies two whole sectors).

Each file is stored on 'unused' sectors and can be read then by a known position and size. However, how do we know what sectors are used or unused? Where are file size and position stored? Where is a file name? These answers are given by a file system.

As a whole, file system is structured data representation and a set of metadata describing the stored data. A file system not only serves for the purposes of the whole storage but is also a part of an isolated storage segment – disk partition. Usually, the file system operates blocks, not sectors. File system blocks are groups of sectors which optimize storage addressing. Modern file systems generally use block sizes from 1 to 128 sectors (512-65536 bytes). Files are usually stored from the start of a block and take entire blocks.

Immense write/delete operations to file system cause file system fragmentation. As a result files aren't stored as whole fragments and are divided into fragments. For example, a storage is entirely taken by files with size about 4 blocks (e.g. a collection of pictures). User wants to store a file that will take 8 blocks and therefore deletes the first and the last files. By doing this it clears the space on 8 blocks, however, the first segment is near to the storage start, and the second – to the storage end. In this case 8-block file is split into two parts (4 blocks for each part) and takes free space 'holes'. The information about both fragments as parts of a single file is stored to file system.

In addition to user’s files, the file system also contains its own parameters (such as block size), file descriptors (including file size, file location, its fragments etc.), file names and directory hierarchy. It may also store security information, extended attributes and other parameters.

To comply with diverse requirements as storage performance, stability and reliability plenty of file systems are developed to serve certain user purposes.

Windows file systems:

Microsoft Windows OS uses two major file systems: FAT, inherited from old DOS with its later extension FAT32, and widely-used NTFS file systems. Recently released ReFS file system was developed by Microsoft as a new generation file system for Windows 8 Servers.

FAT:
FAT (File Allocation Table) is one of the simplest types of a file system. It consists of a file system descriptor sector (boot sector or superblock), a file system block allocation table (referred as File Allocation Table) and plain storage space to store files and folders. Files on FAT are stored in directories. Each directory is an array of 32-byte records, each defining file or file extended attributes (e.g. long file name). File record attributes the first block of a file. Any next block can be found through a block allocation table by using it as linked-list.

Block allocation table contains an array of block descriptors. Zero value indicates that the block is not used and non-zero – relates to the next block of the file or a special value for file end.

The numbers in FAT12, FAT16, FAT32 stands for the number if bits used to enumerate file system block. This means that FAT12 can use up to 4096 different block references, while FAT16 and FAT32 can use up to 65536 and 4294967296 accordingly. Actual maximum count of blocks is even less and depends on implementation of a file system driver.

FAT12 was used for old floppy disks. FAT16 (or simply FAT) and FAT32 are widely used for flash memory cards and USB flash sticks. The system is supported by mobile phones, digital cameras and other portable devices.

FAT or FAT32 is a file system, used on Windows-compatible external storages or disk partitions with size under 2GB (for FAT) or 32GB (for FAT32). Windows cannot create FAT32 file system over 32GB (however Linux supports FAT32 up to 2TB).

NTFS:
NTFS (New Technology File System) was introduced in Windows NT and is major file system for Windows at present. This is a default file system for disk partitions and the only file system that is supported for disk partitions over 32GB. The file system is quite extensible supporting many file properties, including access control, encryption etc. Each file on NTFS is stored as file descriptor in a Master File Table and file content. Master file table contains all information about the file: size, allocation, name etc. The first and the last sectors of the file system contain file system settings (boot record or superblock). This file system uses 48 and 64 bit values to reference files, thus supporting quite large disk storages.

ReFS:
ReFS (Resilient File System) is the latest development of Microsoft presently available for Windows 8 Servers. File system architecture absolutely differs from other Windows file systems and is mainly organized in a form of B+-tree. ReFS has high tolerance to failures due to new features included into the system. And, namely, Copy-on-Write (CoW): no metadata is modified without being copied; data is written not over the existing data, but into a new disk space. With any file modifications a new copy of metadata is created into free storage space, and then the system creates a link from older metadata to the newer ones. As a result, a system stores significant quantity of older backups in different places providing easy file recovery unless this storage space is overwritten.

Linux file systems

Open-source Linux OS aims at implementing, testing and using different concepts of file systems. The most popular Linux file systems nowadays are:

• Ext2, Ext3, Ext4 - 'native' Linux file system. This file system falls under active developments and improvements. Ext3 file system is just an extension to Ext2 which uses transactional file write operations with a journal. Ext4 is a further development of Ext3, extended with support of optimized file allocation information (extents) and extended file attributes. This file system is frequently used as a 'root' file system for most Linux installations.
• ReiserFS - alternative Linux file system is created to store huge amount of small files. It has good capability of files search and enables compact files allocation by storing file tails or small files along with metadata in order not to use large file system blocks for the same purpose.
• XFS - file system derived from SGI company and was initially used for company’s IRIX servers. Now XFS specifications are implemented in Linux. XFS file system has great performance and is widely used to store files.
• JFS - file system is developed by IBM for the company’s powerful computing systems. JFS1 usually stands for JFS, JFS2 is the second release. Currently this file system is open-source and implemented in most modern Linux versions.

The concept of 'hard links' used in this kind of OS is a common feature of Linux file systems of not regarding the file name as file attribute and rather defined as an alias for a file in certain directory. File object can be linked from many locations, even multiply from the same directory under different names. This may present serious and even insurmountable difficulties for recovery of file names after file deletion or file system damage.

More about Linux File System Layout:

For convenience, the Linux file system is usually thought of in a tree structure. On a standard Linux system you will find the layout generally follows the scheme presented below.

Subdirectories of the / (root) directory:

Directory	Content
/bin	Common programs, shared by the system, the system administrator and the users.
/boot	The startup files and the kernel, vmlinuz. In some recent distributions also grub data. Grub is the GRand Unified Boot loader and is an attempt to get rid of the many different boot-loaders we know today.
/dev	Contains references to all the CPU peripheral hardware, which are represented as files with special properties.
/etc	Most important system configuration files are in /etc, this directory contains data similar to those in the Control Panel in Windows
/home	Home directories of the common users.
/initrd	(on some distributions) Information for booting. Do not remove!
/lib	Library files, includes files for all kinds of programs needed by the system and the users.
/lost+found	Every partition has a lost+found in its upper directory. Files that were saved during failures are here.
/misc	For miscellaneous purposes.
/mnt	Standard mount point for external file systems, e.g. a CD-ROM or a digital camera.
/net	Standard mount point for entire remote file systems
/opt	Typically contains extra and third party software.
/proc	A virtual file system containing information about system resources. More information about the meaning of the files in proc is obtained by entering the command man proc in a terminal window. The file proc.txt discusses the virtual file system in detail.
/root	The administrative user's home directory. Mind the difference between /, the root directory and /root, the home directory of the root user.
/sbin	Programs for use by the system and the system administrator.
/tmp	Temporary space for use by the system, cleaned upon reboot, so don't use this for saving any work!
/usr	Programs, libraries, documentation etc. for all user-related programs.
/var	Storage for all variable files and temporary files created by users, such as log files, the mail queue, the print spooler area, space for temporary storage of files downloaded from the Internet, or to keep an image of a CD before burning it.

How can you find out which partition a directory is on? Using the df command with a dot (.) as an option shows the partition the current directory belongs to, and informs about the amount of space used on this partition:

yadnesh:/lib> df -h . Filesystem Size Used Avail Use% Mounted on /dev/hda7 980M 163M 767M 18% /