Linux with Operating System Concepts

Reason
Rationale
Multiplatform 
experimentation
For organizations thinking of switching or branching out to different operating 
systems, virtualization gives you the ability to test out other operating systems 
without purchasing new equipment
Cost savings
Software with limited number of licenses can be easily shared via virtualization as 
opposed to placing copies of the software on specific machines. An alternative is to 
use a shared file server. Additionally, as one computer could potentially run many 
different operating systems through virtualization, you reduce the number of 
different physical computers that an organization might need
Scalability
Similar to cost savings, as an organization grows there is typically a need for more and 
more computing resources but virtualization can offset this demand and thus help 
support scalability
Power consumption 
reduction
As with cost savings and scalability, having fewer resources can lead to a reduction of 
overall power consumption
Cross-platform 
software support
Software that only runs on a specific platform can be made accessible to all users no 
matter what platform they are using
Security
The VM is an isolated environment that cannot directly impact the true (outer) 
computer. Thus, malware impacts only the VM
Fault tolerance
Using two or more VMs, you can achieve fault tolerance by shifting the work load 
from one of another in case one VM fails
Administrative 
experience
Virtualization allows you to set up VMs for people who are learning to be system 
administrators so that any mistakes made will not harm the outer (true) computer
Controlling users’ 
environments
An administrator can take remote control of a user’s VM to solve problems
Collaboration
Virtualization allows people to share the same desktop environment in support of 
collaboration
Remote access
Through a VM server, you can access VMs remotely and allow more than one user to 
access a VM at any time

---

Introduction to Linux
◾
21
VMware Player, Virtual Box, CoLinux, Windows Virtual PC, Parallels Desktop, VM from 
IBM, Virtual Iron, QEMU, and Xen. The latter two titles are open source and many of 
these titles have free versions available.
With VM software readily available, we can expand on its capabilities by implementing 
virtualization. With virtualization, an organization hosts a number of VMs through one 
or more VM servers. The servers operate in a client–server networking model where a cli-
ent runs a VM program on the user machine and requests access to one of the stored VMs. 
The VM servers typically store the VMs on a storage area network (SAN). The collection of 
VM servers, the SAN, and the data that make up individual VMs can be called a VM Farm.
Now, accessibility to your VM is one of starting your VM client software and logging 
into the VM server. You select your VM from a list of choices, log into it, and the VM server 
then runs (emulates) the VM for you. Your client operates as an input/output device while 
the processing and storage take place on the VM server. As you make modifications to your 
VM, they are saved in the SAN.
There are numerous advantages to virtualization. First is accessibility. You are able to 
access your VM from any computer that has Internet access and runs the proper VM client 
software. Second is cost savings. If your company is small and you cannot afford all of the 
hardware needed for your employees, you can lease or purchase time and space in a VM 
farm where the VM servers and SAN become the hardware that you use.
You can also rely on the company hosting your VMs to handle security and backups 
alleviating some of the IT needs from your own organization. Today, more and more orga-
nizations are taking advantage of virtualization to improve their efficiency and lower costs.
1.6 UNIX AND LINUX
Unix is an old operating system, dating back to 1969. Its earliest incarnation, known as 
MULTICS, was developed for a single platform. It was developed by AT&T Bell Labs. Two 
of the employees, Dennis Ritchie and Ken Thompson, wanted to revise MULTICS to run 
as a platform-independent operating system. They called their new system Unics, with its 
first version being written in the assembly language of the DEC PDP-11 computer so that it 
was not platform-independent. They rewrote the operating system in the C programming 
language (which Ritchie developed in part for Unix) to make it platform independent. This 
version they named Unix.
Numerous versions of Unix were released between 1972 and the early 1980s including 
a version that would run on Intel 8086-based computers such as the early IBM PC and 
PC-compatible computers. Unix was not a free operating system. In spite of it being imple-
mented as a platform-independent operating system, it was not available for all hardware 
platforms.
In 1983, Richard Stallman of MIT began the GNU Project, an effort to complete a Unix-
like operating system that was both free and open source. GNU stands for GNU’s Not 
Unix, an indication that GNU would be a Unix-like operating system but separate from 
Unix. His goal was to have anyone and everyone contribute to the project. He received help 
from programmers around the world who freely contributed to the GNU operating system, 
which they wrote from scratch. Although a completed version of GNU was never released, 

---

22
◾
Linux with Operating System Concepts
the approach taken was to lead to what we now call the open source community. Stallman 
formed the Free Software Foundation (FSF) and defined the GNUs General Public License 
(GPL). We explore open source and its significance in Chapter 13.
At around the same time as the initiation of the GNU Project, researchers at the 
University of California Berkeley developed their own version of Unix, which was given 
the name BSD (Berkeley Standard Distribution) Unix. This version includes networking 
code to support TCP/IP so that these Unix computers could easily access the growing 
Internet. In time, BSD 4.2 would become one of the most widely distributed versions of 
Unix.
The result of several competing forms of Unix led to what some have called the “Unix 
Wars.” The war itself was not restricted to fighting over greater distribution. In 1992, Unix 
System Laboratories (USL) filed a lawsuit against Berkeley Software Design, Inc and the 
Regents of the University of California. The lawsuit claimed that BSD Unix was built, at 
least partially, on source code from AT&T’s Unix, in violation of a software license that UC 
Berkeley had been given when they acquired the software from AT&T. The case was settled 
out of court in 1993.
By 1990, the open software foundation, members of the open source community had 
developed standardized versions of Unix based on BSD Unix. Today, there are still many 
different distributions of Unix available which run on mainframe, minicomputers, and 
servers.
In 1991, a student from Finland, Linus Torvalds, was dissatisfied with an experimen-
tal operating system that was made available through an operating systems textbook of 
Andrew Tanenbaum. The operating system was called Minix. It was a scaled down Unix-
like operating system that was used for educational purposes. Torvalds decided to build his 
own operating system kernel and provide it as source code for others to play with and build 
upon.
*
Early on, his intention was just to explore operating systems. Surprisingly, many 
programmers were intrigued with the beginnings of this operating system, and through 
the open source community, the operating system grew and grew.
The development of Linux in many ways accomplished what Stallman set out to do with 
the GNU project. Stallman and many in the FSF refer to Linux as GNU/Linux as they 
claim that much of Linux was built on top of the GNU project code that had been devel-
oped years earlier.
According to some surveys, roughly 75% of Linux has been developed by program-
mers who work for companies that are investing in Linux. The GPL causes many of these 
programmers to publish their code rather than keeping the code proprietary for the com-
panies they work for. Additionally, 18% of the code is developed strictly by volunteers who 
are eager to see Linux grow.
Today, Linux stands on its own as a different operating system from Unix. In many 
cases, Linux is freely available in source code and the open source community continues to 
contribute to it. And like Unix, there are many distributions. Unlike Unix, however, Linux’ 
*
Torvalds has claimed that had the GNU project kernel been available, he would not have written his own; cited from 
http://web.archive.org/web/20121003060514/http://www.dina.dk/~abraham/Linus_vs_Tanenbaum.html.

---

Introduction to Linux
◾
23
popularity is far greater because, while Unix can run on personal computers, Linux is 
geared to run on any platform and is very effective on personal computers.
Although there are dozens of dialects of Unix, there are hundreds of different Linux 
distributions. Navigating between the available dialects can be challenging. Nearly all of 
the dialects can be categorized into one of four ancestor paths.
• 
Debian
: This branch includes the very popular Ubuntu which itself has spawned doz-
ens of subdialects. Another popular spin-off of Debian is Knoppix.
• 
Red Hat
: There are as many or more subdialects of Red Hat as Debian. The most 
popular subdialect is Fedora. Another popular descendant is Mandrake and another 
is CentOS. Another distribution that is increasing in popularity is Scientific Linux, 
produced by Fermi National Accelerator Laboratory and CERN.
•