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Friday, January 11, 2013

Basic understanding of Unix and Linux

What is UNIX?

UNIX is an operating system which was first developed in the 1960s, and has been under constant development ever since. By operating system, we mean the suite of programs which make the computer work. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops.
UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment.
However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no windows interface available, for example, in a telnet session.

The UNIX operating system is made up of three parts:

1.      The kernel:
The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls

2.      The shell:
The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out.

3.      The programs:
The commands are themselves programs: when they terminate, the shell gives the user another prompt (%).
Files and processes: Everything in UNIX is either a file or a process.
A process is an executing program identified by a unique PID (process identifier).
A file is a collection of data. They are created by users using text editors, running compilers etc.

Starting an UNIX terminal: To open an UNIX terminal window, click on the "Terminal" icon from Applications/Accessories menus.An UNIX Terminal window will then appear with a % prompt, waiting for you to start entering commands

What is LINUX?

Linux is an open source operating system, which is kind of an adapted clone of a UNIX operating program. In the beginning, during the nineteen sixties to eighties computer devices were huge, cumbersome things that had been only depending on codes to get useful. A standard user wasn’t able to run a computer if he wasn’t very cognisant of various techniques of coding and he usually had to have access to the resources of a large corporation, the federal government or a well-funded university.
Computer geeks and nerds arrived with a hunger to acquire quicker, simpler and even more powerful systems that might not be restricted to large mainframe computer departments and programming gurus came up with a changed and improved model of UNIX named – Linux

Mainly because persons have grown to love the GUI program of Windows, Linux for a long time wasn’t commonly used by the ranked masses of home users. Even so, programmers, professional laptop developers and server-side buyers acclaim Linux for being the finest running system available.
Linux now has solid safety measures, and functions fantastically in the arena of server and hosting solutions. On the other hand, for most consumers this OS has some issues outstanding in that it appears incompatible with a variety of computer softwares, the being mostly Windows–based utils and games.

What is the difference between Linux and UNIX operating systems?
·        UNIX is copyrighted name only big companies are allowed to use the UNIX copyright and name, so IBM AIX and Sun Solaris and HP-UX all are UNIX operating systems. The Open Group holds the UNIX trademark in trust for the industry, and manages the UNIX trademark licensing program. Most UNIX systems are commercial in nature.

·        Linux is a UNIX Clone. If you consider Portable Operating System Interface (POSIX) standards then Linux can be considered as UNIX.
Linux is a Unix clone written from scratch by Linus Torvalds with assistance from a loosely-knit team of hackers across the Net. It aims towards POSIX compliance.

·        Linux is just a kernel.
All Linux distributions includes GUI system, GNU utilities (such as cp, mv, ls, date, bash etc.), installation & management tools, GNU (c/c++ Compilers), Editors (vi) and various applications (such as OpenOffice, Firefox).
Whereas, most UNIX operating systems are considered as a complete operating system as everything come from a single source or vendor.

·        Linux is Free. You can download it from the Internet or redistribute it under GNU licenses.
Whereas, Most UNIX like operating systems are not free (but this is changing fast, for example OpenSolaris UNIX). However, some Linux distributions such as Redhat / Novell provide additional Linux support, consultancy, bug fixing, and training on cost of additional fees.

·        Linux is considered as most user friendly unix-like operating systems. It makes it easy to install sound card, flash players, and other desktop goodies.
Whereas, Apple OS X is most popular UNIX operating system for desktop usage.

·        Linux comes with open source netfilter/iptables based firewall tool to protect your server or desktop.
Whereas, UNIX operating systems comes with its own firewall product (for example Solaris UNIX comes with ipfilter based firewall) or you need to purchase a 3rd party software such as Checkpoint UNIX firewall.

·        Linux by default supports and use ext3 or ext4 file systems.
Whereas, UNIX comes with various file systems such as jfs, gpfs (AIX), jfs, gpfs (HP-UX), jfs, gpfs (Solaris).

·        The differences are not that big for the average end user. They will use the same shell (e.g. bash or ksh) and other development tools such as Perl or Eclipse development tool.
Few popular UNIX Operating System Names:
1.      HP-UX
2.     IBM AIX
3.     Sun Solairs
4.     Mac OS X
5.     IRIX
Few popular Linux Distribution (Operating System) Names:
1.      Redhat Enterprise Linux
2.     Fedora Linux
3.     Debian Linux
4.     Suse Enterprise Linux
5.     Ubuntu Linux

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