Download UNIX-like Operating Systems

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OS
UNIX
UI
Security
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UNIX-like
Operating Systems
by Roman Szturc
Simple, Low-Power Machines
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user had sole use of the machine,
program was loaded into the machine and the
machine set to work,
task is responsible for everything,
task totaly determines behavior of computer.
machines came with libraries of support code which
were linked to the user’s program to assist in
operations such as input and output
This would become the genesis of the modern-day
operating system.
More Powerful Computers
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Later, more powerful computers appeared. They were
characterized as follows:
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CPU is much faster than R/W operations,
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CPU is idle while R/W operation in progress,
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CPU can perform other task while idle.
Need to manage multiple tasks
Task switching.
Task scheduling.
Operating System
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An operating system (OS) is the system (low-level)
software responsible for
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direct control and management of hardware,
task management,
storage allocation,
presentation of a default user interface.
Program and Process
process2
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data2
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process1
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data1
PSfrag replacements
program code
memory
Early Operating Systems
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Early OS had some problems. The OS
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were very diverse — each OS specific to particular
hardware,
used radically different models of commands and
procedures,
Typically, each time the manufacturer brought out
a new machine, there would be a new OS.
UNIX
History
UNIX is an OS developed in the 1960s and 1970s by
AT&T Bell Labs employees including K. Thompson, D.
Ritchie, and D. McIlroy. It was designed to be
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portable,
multi-tasking and
multi-user.
The UNIX systems are characterized by various
concepts:
plain text files,
command line interpreter,
hierarchical file system,
treating devices and certain types of inter-process
communication as files.
Unix Architecture
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PSfrag replacements
shell
utilities
kernel
hardware
Unix-like systems
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UNIX Philosophy
There are the following ideas characterizing the UNIX
philosophy:
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write simple parts connected by clean interfaces.
clarity is better than cleverness,
design programs to be connected to other
programs,
separate policy from mechanism; separate
interfaces from engines,
when a program has nothing surprising to say, it
should say nothing,
when you must fail, fail noisily and as soon as
possible,
design for the future, because it will be here
sooner than you think.
File System
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Every item in a UNIX file system can de defined as
belonging to one of four possible types:
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ordinary file,
directory,
special file,
links.
Pipe
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A pipe “|” sends data from standard output of source
process to standard input of destination process.
if [ $(wget -O - http://www.vltava.cz/...
| grep -c "Perl") -gt 0 ]; then
mail -s "Book" [email protected] << EOF
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You can order the Perl book at vltava.cz.
Your book notifier
.
EOF
fi
User Interfaces
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One of the most heated and ancient battles is over the
choice of Graphical User Interface (GUI) vs. Command
Line Interface (CLI).
Advantages of CLI
structure of UNIX and of its shells allows powerful
mechanisms of piping and redirection,
porting CLI utility to other system is relatively easy
task,
CLI utilities incur much less size and speed
overhead than their graphical counterparts,
textual information is also much smaller than
graphical, obviously making remote connections
less of a pain in the neck.
User Interfaces (continued)
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Advantages of GUI
prettier and more natural feel,
modern computing is very much focused on
media and that is naturally only done with
graphical environments,
graphical desktop allows true multitasking (for the
user) to take place,
an important benefit is the display of dynamically
modifiable abstract information — one click can
replace several commands.
User Interfaces (continued)
Learning Curve
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ability to
use an OS
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PSfrag replacements
CLI
GUI
time
X Window System
X display (Windows)
X screen
Solaris
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X server
X client
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net
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AIX
ag replacements X client
X display (Linux)
X server
X client
X screen
X screen
X client
Window Managers and Desktops
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Window Manager
A window manager is software that controls the
placement and appearance of application windows
under the X Window System. The most popular ones
are: AfterStep, Enlightenment, WindowMaker,
Metacity, TWM, Kwin, MWM, FWM, IceWM, Sawfish, . . .
Desktop
A desktop consists of what is on the screen before any
windows are opened, and what reappears when
windows are closed. It usually shows icons for
programs, documents or folders and possibly an
image as wallpaper. The most popular ones are:
GNOME, KDE, XFCE, CDE.
Security
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OS
Security is inherent part of multiuser OS. It grants
privacy of user data OS stability.
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Authentication
is process by which a computer attempts to
ensure that users are who they say they are.
Authorization
is a process that protects computer resources by
only allowing those resources to be used by
resource consumers that have been granted
authority to use them.
UNIX Distributions
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Over the years there were more than 250 versions of
UNIX-like systems released. The following are the
most significant ones:
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(Net,Free,Open)BSD
Darwin
Mac OS X
(Open)Solaris
Linux
z/OS Unix V1R7
AIX
IRIX
Leading Areas
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Internet backbone,
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multiprocessor systems,
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critical applications,
need of extremely high up-time,
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There are several frequently asked questions
concerning UNIX systems.
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UNIX is more than 30 years-old. Is it worth to
linger with such an antique?
Is UNIX dangerous?
Why should I type a complicated commands
instead of select menu items?
Why UNIX disallows users to do mistakes?