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Linux Basics

So what is Linux all about? Is it only a bunch of files for the operating system and a few utility programs? No it's more than that. The following section gives you the lowdown on this powerful OS.

What Is Linux?
Linux is a freely distributed operating system that resembles Unix in more ways than one. Linux was designed specifically for the PC platform and takes advantage of its design to give users performance comparable to high-end Unix workstations. Many big-name companies like IBM and Compaq have joined the Linux bandwagon, offering systems pre-installed with Linux. Ditto for Linux distributions and applications. Red Hat, Corel, Caldera, Apache, Oracle, etc. are few among the long list of companies offering Linux distributions or applications. More and more businesses are using Linux as an efficient and economical way to run their networks.

Linux is a complete multitasking, multi-user operating system that behaves like Unix in terms of kernel behavior and peripheral support. What's more, it's free! You can download most Linux distributions directly off the Web.

The History Behind Linux
Unix is one of the most popular operating systems for networking worldwide because of its large support base and distribution. Linus Torvalds, who was then a student at the University of Helsinki in Finland, developed Linux in 1991.

From then on Linux fired the imagination of geeks who quickly migrated to this new OS as an alternative to Windows and more expensive Unix systems. Linux gained greater acceptance and popularity when Red Hat released the commercial version of Linux packaged with tech support and documentation. This brought Linux into the limelight as a possible replacement for Windows or Unix on commercial platforms.

Today many corporate enterprises are experimenting with this OS. And with Oracle and IBM migrating their enterprise applications to Linux, this is one OS that promises to capture a major chunk of the enterprise server space.

Linux vs. Other OS
How does Linux compare with other OS? Here's a small comparison of Linux with other OS that may help you understand what makes it so special.

Linux versus Windows 95/ 98
Windows 95/98 is more of a PC operating system and is not used to manage anything more than a small home network. The popularity of Windows 95/98 is based on its low cost and ease of use. As an alternative, Linux can be run on a personal PC, albeit without unleashing its full networking power.

Though commercial software applications for Linux are growing, the number of popular applications is still pitifully small when compared to Windows 95/98.

Linux versus Windows NT
Although, both Linux and Windows NT exhibit different strengths and weaknesses, Linux prevails over NT in the area of networking. Linux is also much smaller that NT and uses less system resources. In addition, Linux crashes less frequently than NT. Linux has been known to run continuously on systems for several months, while NT has a notorious reputation for crashing often.

In the application arena too Linux is slowly catching on with NT. With Oracle, IBM among the few biggies already porting their enterprise applications to Linux, this is one OS that holds the potential to upset Windows dominance.

Linux versus Unix
In terms of features, Unix and Linux are quite similar. However, the major difference between Unix and Linux is that Unix was designed specifically for networking. Linux runs perfectly fine as a personal Unix system and on large servers. Also, unlike Unix, Linux is free.

Linux supports a much wider range of hardware than Unix and because of the open source model, any driver for certain hardware can be written for Linux as long as someone has the time to do so.

System Features
Linux is a complete multitasking, multi-user operating system that behaves like Unix in terms of kernel behavior and peripheral support. Linux has all the features of Unix, plus several recent extensions that add new versatility. The source code for Linux, as also most common utilities are available for free.

The Linux kernel was originally developed for the Intel 80386 CPU's protected mode. The 80386 was designed with multitasking in mind (despite the fact that most Intel CPUs then ran on the single-tasking DOS), and Linux makes good use of the features built into the CPUs instruction set. Linux works well on any 80486, Pentium—class, Celeron, as also on competing Intel clones from AMD.

Linux allows shared executables, so if more than one copy of a particular application is loaded (by either one user running several identical tasks or several users running the same task), all the tasks can share the same memory.

The Linux kernel also supports demand paging, which means that only sections of a program that are necessary are read into RAM. To further optimize memory usage, Linux uses a unified memory pool. To support large memory requirements when only small amounts of physical RAM are available, Linux supports swap space. Swap space enables pages of memory to be written to a reserved area of a disk and treated as an extension of physical memory.

Linux uses dynamically shared libraries extensively. Dynamically shared libraries use a common library section for many different applications, effectively reducing the size of each application. Linux does not allow full library linking (called statically linked libraries) for portability to machines that may not have dynamic libraries.

Linux supports a number of different file systems, including those compatible with DOS, Windows NT and OS/2. Linux's own primary file system, called ext2fs, is designed for optimal use of hard disk space.

Linux is ideally suited for networking (as a print and file server), Web hosting, and application development. Many of the Linux compilers, tools, debuggers, and editors are from the Free Software Foundation's GNU project.

X Windows
X Windows is a graphical user interface (GUI) designed at MIT to provide portable GUI applications across different platforms. The version of X supplied with Linux also called Xfree86 and is a direct port of the standard X11R5 system to 80386-based architectures. Xfree86 has been extended to provide compatibility with some other GUIs, including OpenLook.

Xfree86 supports several different video cards at different resolutions, offering a high-resolution graphical interface. Any X application can be recompiled to run properly under Linux, and a number of games, utilities, and add-ons have been developed and supplied as part of the X system. The Xfree86 system also includes application development libraries, tools, and utilities using which programmers can write applications specifically for X Windows.

DOS Interface
Linux provides emulators, which allow many DOS and Windows applications to be executed directly from within Linux as part of the distribution system. Don't expect complete portability of applications though, as some applications are written to access peripherals or disk drives in a manner that Linux can't handle. Although Linux can emulate DOS and Windows, the emulation feature is not intended to support full usage. Instead, it provides the occasional user the ability to run an application under Linux. For heavy use, your system should be set up with Windows, and Linux in separate partitions, enabling you to enter any one at boot time.

Linux allows you to transfer files seamlessly between the Linux file system and DOS/Windows by accessing FAT partitions on a hard disk directly, if configured accordingly. This capability makes it easy to move files and applications back and forth between the two operating systems.

How Secure Is A Linux Server?
User Accounts: The root (superuser) controls all user accounts and can lock out one or more at any time.

Discretionary Access Control: With DAC, the root can control how users access files and restrict their degree of access.

Network Access Control: The superuser can control who has access to the server and to what extent.

Encryption: Linux provides a wide variety of encryption mechanisms.

Logging, Auditing And Network Monitoring: Logs all system & kernel messages, network connections, remote user requests, processes under user control and every command issued by a specified user.

Intrusion Protection: Linux is inbuilt with wide range of tools to build Firewalls.

Intrusion Detection: Linux logs intrusion attempts and can alert the superuser.

What Platforms Does Linux Run On?