An Introduction To Linux Concepts Information Technology Essay

An operating system is a package plan that acts as an interface between a user and a computing machine. It consists of instructions that are given to the hardware constituents of the computing machine to execute specific undertakings, such as making or copying paperss and sing them. Some illustrations of operating systems are Linux, Windows XP, Windows 7, Solaris, Mac, and UNIX.

Another ground for Linux ‘s popularity is that unlike proprietary operating systems, its beginning codification is freely available to anyone. As a consequence, big communities of users and developers have contributed to do the operating system rich and versatile in characteristics. Many persons and communities have used the Linux beginning codification to develop different types of Linux-based runing systems, which are called distributions. Some of the popular Linux distributions are: Debian, Fedora, Red Hat, SUSE, and Ubuntu.

1.2 Open Source Software

In this subject, you will larn what unfastened beginning package is and how it is different from closed beginning and free package. You will besides place the assorted unfastened beginning package and applications available. Last, you will larn about licensing.

1.2.1 Specifying Open Source

The unfastened beginning package is free package. The term free does non mention to the cost of the package. Alternatively, it refers to the freedom given to the users to suitably modify the plan. The unfastened beginning package allows users to freely utilize its beginning codification and custom-make it to run into single demands.

Note: The unfastened beginning package can be used as it is or can be redistributed after doing alterations to it.

The unfastened beginning package allows users to:

Access the beginning codification of the package.

Run the package for commercial or personal usage.

Custom-make the beginning codification to run into specific demands.

Redistribute transcripts of the package.

Let go of the customized package to the populace in general.

However, this redistribution of transcripts with or without alterations may or may non be free. The individual or bureau redistributing the package may bear down the terminal user the costs involved in media and redistribution.

You may besides better the beginning codification and redistribute the package for a fee. Alternatively, you may administer the improved beginning codification free of cost but charge the users for services, such as ascents, additions, or support.

For illustration, Fedora Linux is available free of cost for terminal users along with the ascents, sweetenings, and additions to the operating system. However, Red Hat Enterprise Linux beginning codification is free but end users have to pay a fee for ascents, additions, and support.

1.2.2 Comparing Open Source with Closed Beginning

Open beginning package is besides different from closed beginning or proprietary package. The proprietary package beginning codification is non released to stop users and is merely available in a compiled feasible province. The terminal users have to buy the package to utilize it for personal or commercial intents. In add-on, copying or redistribution of the package may be restricted by the licence understanding between the seller and the terminal user.

Closed beginning package are by and large owned, developed, and distributed by a individual seller to stop users who purchase the package for a license fee. Servicess, such as ascents, additions, and support are defined by the licence understanding between the seller and the terminal user. These may change as per the merchandising and distribution scheme of the seller.

1.2.3 Identifying Open Source Operating Systems and Applications

The assorted unfastened beginning runing systems are:

Open Solaris: Is an unfastened beginning runing system sponsored by Sun Microsystems.

Fedora Linux: Is an unfastened beginning Linux operating system sponsored by Red Hat. It has a release rhythm of six months.

Red Hat Enterprise Linux: Is an unfastened beginning Linux runing system by Red Hat. However, end users have to pay subscription fee for support and other public-service corporations shipped along with Red Hat Enterprise Linux.

Open SuSE: Is an unfastened beginning Linux-based operating system sponsored by Novell. Open SuSE is a German distribution. There are a batch of applications and public-service corporations packed along with Open SuSE Linux. It besides contains StarOffice ( Private Edition ) and Word Perfect ( Private Edition ) . It is really popular in Europe.

Mandrake Linux: Is an unfastened beginning Linux operating system. Mandrake offers the power and stableness of Linux to both single and enterprise users in a user-friendly environment. It contains assorted high-quality applications, such as a complete Office Suite of plans. It besides provides a constitutional installing support.

Debian Linux: Is an unfastened beginning Linux-based operating system sponsored by the Debian community. Debian is among the earliest distributions of Linux and is available free of cost. It offers precompiled package bundled with more than 8000 bundles and an easy installing process.

The assorted unfastened beginning applications are:

Apache Web Server: Is an unfastened beginning Web waiter sponsored by Apache Software Foundation. It runs on assorted runing system platforms including UNIX, Linux, Solaris, and Windows. It besides provides support for a assortment of characteristics runing from server-side scheduling linguistic communication to multiple hallmark strategies.

Sendmail: Is an unfastened beginning get offing application sponsored by the Sendmail Consortium. It is a general intent internetwork e-mail routing application. It besides supports assorted types of mail transportation and bringing methods, including Simple Mail Transfer Protocol ( SMTP ) . Sendmail is besides available in many proprietary versions.

MySQL: Is an unfastened beginning database application sponsored by Sun Microsystems.

1.2.4 Licensing

Open beginning package can be used for a assortment of intents to accommodate single demands. There are many types of licences that legalize the usage of unfastened beginning package for assorted intents.

Some illustrations of unfastened beginning licences include:

General Public License ( GPL ) : Allows users to box and redistribute the original or modified beginning codification of the package merely with other GPL licensed package. It does non let the unfastened beginning package to utilize any other proprietary package.

Lesser General Public License ( LGPL ) : Allows users to box and redistribute the original or modified beginning codification of the package merely with other LGPL licensed package. In add-on, it allows the usage of proprietary package with LGPL licensed unfastened beginning package.

Berkeley Software Distribution ( BSD ) : Allows redistribution of the unfastened beginning package with any other package. It allows distribution of original beginning codification after alteration even if it uses some other package non covered under the BSD licence. In add-on, it allows the usage of proprietary package with BSD covered package.

1.3 Beginning of Linux

In the earlier yearss of computing machines, developers were looking for an operating system, which was simple and elegant, flexible, and secure. At that clip, the developers of Bell Laboratories introduced an operating system that fulfilled all these demands. This bit by bit evolved into the UNIX runing system.

Linux was derived from UNIX to supply a free or really low-priced operating system to computing machine users. It is considered to be a really efficient and fast-performing operating system.

1.3.1 History of Linux

The name of the Linux operating system was coined by Linus Torvalds in 1991. Linux was developed on Minimal UNIX ( MINIX ) , a UNIX version, utilizing GNU ‘s Not UNIX GNU C compiler.

Unix

In 1965, Bell Labs and Massachusetts Institute of Technology ( MIT ) along with General Electric developed one of the first multiuser computing machine systems, called Multiplexed Information and Computing Service ( Multics ) . Ken Thompson and Dennis Ritchie, two Bell Labs applied scientists, worked on this undertaking until 1969.

Subsequently, they developed another operating system in C linguistic communication. This added flexibleness in porting the operating system to other calculating platforms, which was non easy with Multics as it was written in assembly linguistic communication. This operating system was named Uniplexed Information and Computing Service ( Unics ) , which was similar to the Multics operating system. The name Unics was so changed to UNIX.

In 1972, Ken Thompson and Dennis Ritchie re-wrote UNIX utilizing the C scheduling linguistic communication. Around 1974, UNIX was licensed to universities for educational intents and, a few old ages subsequently, it was made available commercially.

Berkeley Software Distribution ( BSD )

During 1976-1977, Ken Thompson was on sabbatical for six-months from Bell Labs to learn as a visiting professor at the Computer Science Department at the University of California-Berkeley ( UCB ) . He taught the UNIX runing system. His Sessionss were really popular.

When Thompson returned to Bell Labs, pupils and professors at Berkeley continued to heighten UNIX. Finally, all these sweetenings got incorporated into BSD Version 4.2.

Minix

MINIX was another version of UNIX, which was used as a instruction assistance in universities and colleges. It was a free UNIX ringer available with all the beginning codification. Due to its little size, micro kernel-based design, and ample certification, it was good suited to people who wanted to run a UNIX-like system on their personal computing machine.

It is interesting to observe that MS-DOS was created much later than UNIX. By that clip, the industry had begun to accept UNIX as the criterion operating system. Therefore, UNIX characteristics have influenced the design of MS-DOS. Many sellers, such as Sun, IBM, and Hewlett-Packard, purchased the beginning codification of UNIX. They developed their ain versions of UNIX.

This resulted in many differences amongst assorted versions of UNIX offered by assorted companies. To avoid the confusion, some criterions called Portable Operating System Interface ( POSIX ) , were outlined. POSIX is a set of criterions that enabled package to run on assorted UNIX-based runing systems without altering the beginning codification.

Note: POSIX is produced by the Institute for Electrical and Electronic Engineers ( IEEE ) and recognized by International Organization for Standardization ( ISO ) and American National Standards Institutes ( ANSI ) .

In 1983, an MIT scientist, Richard M. Stallman, launched the GNU ‘s Not UNIX ( GNU ) undertaking. The chief purpose of this undertaking was to make a UNIX-like operating system but free from licensing charges. Under this undertaking, the GNU operating system was distributed to coders around the universe to better it.

To form the work on the GNU undertaking, Stallman and other people created the Free Software Foundation ( FSF ) . This organisation promoted the development and usage of free package. FSF developed the GPL to construct a organic structure of free package protected from those who would utilize it to make proprietary closed-source systems. The organisation charges a little fee to run the foundation. Around 1990, FSF had developed a figure of tools that could be freely modified and redistributed.

1.3.2 Development of Linux

Around 1991, Linus Torvalds, a pupil at the University of Helsinki, Finland, was working on Minix. Linus Torvalds liked the characteristics of the UNIX runing system and wanted to make his ain version of the UNIX runing system. After he created this operating system, he gave it free of charge for everybody to utilize. Torvalds worked on the undertaking, wrote the beginning codification for the meat, and named it Linux. The meat was the nucleus plan of the Linux operating system. Torvalds made the Linux kernel available on the Internet.

The Linux meat was combined with the GNU system ensuing in a complete operating system. This operating system was called GNU/Linux because it was a combination of the GNU system and Linux as the meat. The GNU/Linux operating system is referred to as the Linux operating system. Like other runing systems, it has a meat in its nucleus. The meat controls the resources of the computing machine and signifiers an interface between the user and the hardware.

Linux follows the unfastened development theoretical account. Torvalds has made the beginning codification of the Linux meat available for survey and alterations on the Internet. This means that the current development version of Linux is ever unfastened to everybody. Torvalds besides accepts alterations to the meat codification. The consequence is that whenever a new version of Linux with new functionality is released, people work on the new version to repair bugs, if any. To keep stableness, Torvalds exercises rigorous quality control and so merges all the new codification into the meat. This is in contrast to a closed theoretical account, in which a undertaking squad works on the package version and there are long intervals before people use the package and repair the mistakes in it.

By looking at the version figure of Linux, you can state if it is a stable or test version. In version 1.x.y, if x is an even figure, it signifies a stable version of Linux. Conversely, if x is an uneven figure, it signifies a beta ( test ) release of Linux.

The Internet has played a major function in the development of the Linux operating system. Today, many companies provide support for Linux on the Internet. Many Linux forums on the Internet allow free enrollment and subscription to the latest information. The official mascot for Linux is the Linux penguin, called Tux. This mascot was selected by Linus Torvalds.

The undermentioned figure ( Refer to Figure 1.1 ) shows the Linux functionary mascot.

Figure 1.1: The Linux Official Mascot

1.3.3 Features of Linux

The characteristics of the Linux operating system are:

Multiprogramming: Allows plans to be executed at the same time utilizing the same set of calculating resource. In Linux, concurrent execution is made possible by utilizing the construct of time-sharing. This means that the operating system has to pull off assorted plans to be executed. These plans are queued and Central Processing Unit ( CPU ) clip is shared among them. Each of the running plans get CPU clip for a specific period and are so put back in the waiting line to wait for its bend once more. In the average clip, the following plan in the waiting line is attended.

Multitasking: Is the ability of any operating system to manage the executing of multiple undertakings. While a undertaking is waiting for the completion of an activity, the CPU begins with the executing of the following task.while one undertaking is waiting for input from the user, another plan could be put ining an application. To explicate the construct of multitasking, see an illustration where you are holding your breakfast, watching a Television, and speaking to your female parent over the phone. You are executing more than one undertaking at the same time. However, at a given point in clip, you would be taking a bite, watching the Television, or talking on the phone. This means, you divide your clip amongst all the undertakings. Similarly, the CPU divides the clip among all the active undertakings. The meat is responsible for scheduling the undertakings.

Virtual memory: Is an extra memory that an application can utilize when the physical memory is already consumed. This means some portion of the difficult disc is made available for the application, to be used as the practical memory. The sum of physical memory may non ever be sufficient to run big applications or to hold multiple applications active at a point in clip. The system places infrequently required plans and informations in the practical memory and loads them in the memory, whenever required. Therefore, it uses the resources of the computing machine to the optimum.

Shared libraries: Are sets of maps or subprograms maintained as a set of files. Multiple applications can entree the needed maps from the shared library files alternatively of separately keeping codification for the maps. This saves difficult disc infinite and memory.

POSIX-compliance: Supports most of the criterions set for all UNIX systems.

Obeche: Is derived from the Server Message Block ( SMB ) protocol of the Microsoft runing systems to portion file and print services. Samba is a suite of plans that implement the SMB protocol in Linux. It allows you to portion a Linux file system with the Windows operating system and besides portion a Windows file system with Linux.

Note:

A protocol is a set of regulations that states the communicating criterions for informations transportation between two applications.

The term file system refers to a mechanism used by an operating system to hive away and pull off files and directories on a storage medium.

A divider is a logical part of the difficult disc, which is created utilizing either the operating system-based public-service corporation or any third-party public-service corporation.

Network Information Service ( NIS ) : Allows you to make user histories that can be shared across multiple computing machines in a web. It is a client and server database system that acts as a cardinal database of history information used for history hallmark.

Office suites: Are supported by Linux. Basically, Linux supports OpenOffice.org, which is a set of plans that has many in-built tools. OpenOffice.org enables you to make paperss, presentations and illustrations, and analyze informations. OpenOffice.org provides a set of applications merely like Microsoft Office Application for Windows.

Data file awaying public-service corporations: Are the public-service corporations provided by Linux for basic informations backup ( file awaying ) , such as pitch, cpio, and Doctor of Divinity. Advanced Maryland Automatic Network Disk Archiver or Amanda is a backup system supported by Linux. It enables the Local Area Network ( LAN ) decision maker in puting up a maestro backup waiter and do back up for multiple hosts in a big capacity tape thrust.

Web waiter: Linux comes with the Apache Web waiter, one of the most popular Web waiters in usage today. Apache besides supports the Squid placeholder waiter that helps to better the public presentation for accessing the Internet.

Licensing: For Fedora means that anyone can download, put in, or utilize the package and any updates to the package, irrespective of the bringing mechanism. Linux is a right of first publication under the GNU GPL.

Extra characteristics: Include utile and free package, such as text editors, browsers, and scientific applications.

1.4 Basic Principles of Linux

The basic rules of the Linux package include:

Stability and Dependability

Security

Stability and Dependability

Linux is a stable operating system, which does non necessitate to be restarted sporadically to keep public presentation degrees. It provides equal protection against stop deading up or decelerating down over clip due to issues, such as disc defragmentation and clogging of impermanent files. This consequences in increased uptime.

Linux is modular by design. This means that you can merely put in applications that are truly needed. This saves a batch of resources that would travel waste in pull offing unneeded applications and public-service corporations that otherwise come bundled with non-modular runing systems. It besides helps Linux to stay extremely customizable and easy to keep and pull off.

As a multiuser operating system, everything in Linux is managed as a file and all the constellations are stored in text format. The package constituents of Linux are individual purpose plans and are designed to work together to execute complex undertakings in a multiuser environment. This helps Linux perform better even with less resources.

The assorted public-service corporations and plans of the Linux operating system are majorly unfastened beginning. A big community of developers and users are at that place to prove, modify, and better them. Therefore, bugs are reported and fixed comparatively faster every bit compared to proprietary operating systems. A big developer base besides consequences in frequent ascents and improved releases to take attention of any defects in the operating system.

Security

Linux provides a figure of characteristics that cater to assorted security demands at personal, commercial, and organisational degrees. The assorted Linux security characteristics include:

File System Security: Linux has a hierarchal file system that keeps similar files, such as informations, plans and constellation files at fixed locations in a structured manner. This allows better arrangement of security policies to guarantee safety for the file system.

Firewall Security: Linux provides a extremely customizable and unafraid firewall that can provide to assorted personal and commercial demands. It supports really simple yet effectual constellations to really complex constellations providing to commercial or organisation scenarios.

Run Levels Security: Linux provides tally degrees with a predefined set of services being available in peculiar tally degrees. These tally degrees can besides be customized to include or except services accommodating to user demands. The tally degrees help users originate and run minimal figure of services required. This non merely helps in salvaging cherished calculating resources but besides reduces surface country for any security menaces.

Servicess: Linux services are known as devils. These devils can be configured to run under mulct grained user degree security. For illustration, a user in Linux can merely run the services meant to be run by him or her merely. This prevents the possibility of an onslaught that can compromise the full computing machine at a clip.

Security Enhanced Linux: Linux provides Security Enhanced Linux ( SELinux ) which provides better entree control and security at the meat degree through security policies. SELinux runs applications into assorted sandboxes and isolates them from each other and the underlying operating system.

Discretionary Access Control ( DAC ) : Linux utilizations DAC to guarantee security in a multiuser environment. This means that the files and directories are labeled with a set of permissions to bespeak:

The user or group, the object belongs to

The types of operation they can execute on it, such as read, compose, or run

Advantages of Linux Operating System

The Linux operating system has several advantages. Some of the advantages are listed in Table 1.1.

Advantages

Description

Dependability

Linux waiters need non be shut down for old ages together. This means that users do non confront any operating system failures.

Backward compatibility

This means that Linux supports older hardware. It can run on assorted types of processors, such as 386 and 486 Intel processors. In add-on, it can run on DEC Alpha, Sun SPARC, PowerPC, and SGI MIPS.

Simple installing and upgrade procedure

Most Linux versions have menu-driven and easy installing processs. In add-on, it provides the ability to upgrade from anterior versions easy. In the upgrade procedure, the system uses the bing constellation files and maintains a list of its actions during installing.

Low entire cost of ownership

The entire cost of implementing Linux waiter package is low. In add-on, the cost of support can besides cut down as there are a batch of people and organisations supplying free support for Linux. The system constellation demands for put ining a Linux computing machine are less. For this ground, the hardware and care cost goes down.

Support for bequest devices

Linux can besides run on a computing machine which has low constellation.

Graphic User Interface ( GUI )

Ten Windows system is the graphical interface for Linux. It is divided into two subsystems dwelling of a waiter and a client. The assorted GUIs provided by Linux are K Desktop Environment ( KDE ) and GNU Network Object Model Environment ( GNOME ) . Both of these GUIs are the versions of the X Window system.

Excellent security characteristics

Linux offers a secure firewall, entree control, and customized tally degrees to guarantee security.

Support for development libraries

Linux offers assorted platforms for many development linguistic communications, such as C, C++ , JAVA, Python, and Perl. It besides supports Integrated Development Environments ( IDE ) , such as KDevelop and Glade.

Support for high user burden

Linux can back up a big figure of users working at the same time. The restriction is typically because of the waiter hardware.

Table 1.1: Advantages of Linux Operating System

1.5 Red Hat Operating System Distributions

Red Hat Inc. provides different discrepancies for assorted types of users. It has divided its users into the undermentioned two classs:

Business Users: The first class includes the concern users who need an operating system that requires fewer updates. Red Hat provides the Red Hat Enterprise Linux merchandise suite for these users. These users need to pay a license fee for the package. The alterations in the operating system are made at a low gait so that concern users need non upgrade the operating system at frequent intervals.

Other Users: The 2nd class includes the users who use Linux for experimental intent and do usage of its new and advanced characteristics. These users use the package without paying any license fee. They can download the package from the Internet and utilize it free of charge. For illustration, Fedora is a freely downloadable runing system.

The assorted Linux discrepancies provided by Red Hat Inc. are:

Red Hat Enterprise Linux suite: Runs on multiple hardware architecture such as IBM PowerPC, AMD64, Intel EM64T, and Intel x86/x64. The runing systems of the Red Hat Enterprise Linux suite are:

Red Hat Enterprise Linux AS: Used for big waiters and supports up to 16 CPUs. This operating system supports databases, Enterprise Resource Planning ( ERP ) , and Customer Relationship Management ( CRM ) applications.

Red Hat Enterprise Linux ES: Used for little and in-between scope waiters and supports up to two CPUs. It is used for concern applications, such as printing, mailing, and networking applications.

Red Hat Enterprise Linux WS: Used as desktop operating system and supports up to two CPUs. This operating system is compatible with Red Hat Enterprise Linux AS and Red Hat Enterprise Linux ES. This operating system is suited for client applications, such as papers processing and package development applications.

Red Hat Desktop: Is used for little and medium concern groups, back uping a individual CPU. It is compatible with Red Hat Enterprise Linux AS, Red Hat Enterprise Linux ES, and Red Hat Enterprise Linux WS. This operating system is suited for papers processing, Web browse, package development, and instant messaging.

Fedora Core: Represents a all-purpose operating system holding capablenesss comparable to other runing systems, such as Windows NT and Macintosh. Fedora Core is a Red Hat-sponsored undertaking but Red Hat Inc. does non back up it. You can download Fedora free of charge from assorted Web sites. The official Web site for Red Hat is http: //www.Red Hat.com.

Red Hat Enterprise Linux has the undermentioned versions released over clip:

Red Hat Enterprise Linux 2.1 ( Panama )

Red Hat Enterprise Linux 3 ( Taroon )

Red Hat Enterprise Linux 4 ( Nahant )

Red Hat Enterprise Linux 5 ( Tikanga )

Red Hat Enterprise Linux 6 ( Santiago )

Red Hat Enterprise Linux is closely related to the Fedora Linux community undertaking sponsored by Red Hat. Every Red Hat Enterprise Linux version takes engineerings from Fedora after considerable stabilisation and quality confidence attempt. While Fedora nucleus has a six month release rhythm, Red Hat Enterprise Linux has a more conservative release rhythm of two old ages.

Even earlier, Red Hat Enterprise Linux versions were besides based on Red Hat ‘s unfastened beginning Red Hat Linux runing system. But afterwards, Red Hat Linux split into community-based Fedora undertaking and commercial Red Hat Enterprise Linux. The latest Red Hat Enterprise Linux 6 has many characteristics of Fedora 13 and Fedora 14.

However, Fedora is a community undertaking that serves as an upstream version for Red Hat Enterprise Linux. Red Hat Enterprise Linux serves as a commercial endeavor runing system that is released as alpha and beta versions before concluding release.

Since Red Hat Enterprise Linux is an unfastened beginning runing system and its beginning codification can be accessed by anyone, there are certain runing systems, which use Red Hat Enterprise Linux beginning codification. Users compile their ain versions of Red Hat Enterprise Linux. One such popular operating system is CentOS. These rebuilds provide free updates from non-Red Hat waiters. However, these runing systems do non acquire any support from Red Hat.

Drumhead

In this session, you learned that:

An operating system is a package plan that acts as an interface between a user and a computing machine.

Linux is chiefly derived from the UNIX runing system.

The unfastened beginning package is a free package and closed beginning package are by and large proprietary package owned,

Some of the illustrations of the unfastened beginning licences include:

General Public License ( GPL )

Lesser General Public License ( LGPL )

Berkeley Software Distribution ( BSD )

Linux was developed on MINIX, a UNIX version, utilizing GNU C compiler.

The official mascot for Linux is the Linux penguin, called Tux.

The characteristics of the Linux operating system are:

Multiprogramming

Multitasking

Virtual memory

Shared libraries

POSIX-compliance

Obeche

Network Information Service ( NIS )

Office suites

Data archiving public-service corporations

Web waiter

Licensing

The basic rules of the Linux package include:

Stability and Dependability

Security

The Linux operating system provides assorted advantages, such as backward compatibility, simple installing and upgrade procedure, and low sum cost of ownership.

Exercise

Linux is chiefly derived from the _____ operating system.

The unfastened beginning package is a ____ package.

Open Solaris is an unfastened beginning runing system sponsored by _________ .

The official mascot for Linux is the Linux penguin, called ______ .

_________ allows plans to be executed at the same time utilizing the same set of calculating resource.

The basic rules of the Linux package include ________ and _______ , and _______ .

Answers to Exert

Unix

free

Sun Microsystems

Dinner jacket

Multiprogramming

stableness, dependability, security

Glossary

A

Apache Web Server:

It is an unfastened beginning Web waiter sponsored by Apache Software Foundation.

C

Closed Beginning Software

Closed beginning package are by and large owned, developed, and distributed by a individual seller to stop users who purchase the package for a license fee.

Meter

MySQL

It is an unfastened beginning database application sponsored by Sun Microsystems.

Oxygen

Open Source

The unfastened beginning is a free package that allows users to freely utilize its beginning codification and custom-make it to run into single demands.

Second

Sendmail

It is an unfastened beginning get offing application sponsored by the Sendmail Consortium. It is a general intent internetwork e-mail routing application.