What
Is UNIX Operating system?
InWhatthe
narrowestIsUNIX?senses
UNIX is a time-sharing operating system kernel: a program that controls the
resources of a computer and allocates them among its users. It lets users run
their programs; it controls the peripheral devices and it provides the file
system that manages the long-term storage of information.
In the broader sense, it is often taken
to include not only the kernel but also essential programs like compilers,
editors, command languages etc.
Still
more broadly, it may even include programs developed by you and other users.
The UNIX system is full duplex system: the characters that you type on the
keyboard are sent to the system which sends them back to the terminal to be
printed on the screen.
The UNIX
system primarily contains three components:
1.) The
user.
2.) The
Shell.
3.) The
kernel.
The user
means you who is using the operating system to fulfill the needs.
The
shell means the interface between the user and the kernel. A user never
directly talks to the kernel because it is pretty difficult to do that. Of
course you would never like to talk to the kernel in assembly language or so
making your job harder and time consuming. The shell does this job for you i.e.
it interacts with the kernel.
LinuxIntroductionanNix
operatingToRedhatsystemLinuxhas
all its inherent properties from open UNIX projects. Like all other UNIX like
systems it is a flavor of UNIX system and is most widely accepted worldwide at
present. In only less than a decade of its development it has gained worldwide
recognition in all phases of this Industry.
Linus Torvalds of the University of
Helsinki in Finland originally created Linux. In the year 1991 Linux was made
public. Linus made the source code freely available and encourage others to
freely develop it further. The current stable version of Linux is 2.2.5-15.
Much of the software is developed by Free Software Foundation’s GNU project. It
is therefore free.
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TheAdvantagesLinuxhaveOf
followingLinux advantages over UNIX:
1.) Linux is free.
2.) Linux
can run on as little as 150Mb of space and can run on as little as 2 Mb of Ram.
3.)
Full Multitasking OS.
4.) A
portion of the hard disk can be used as the Ram thus creating room for virtual
Ram.
5.)
It have got windows like X-Windows system. 6.) It uses standard TCP/IP
protocols.
7.) The
source code is freely available.
Why To
Use Redhat Linux
There1.) areItisseveralbasedonreasonscurrenttostableuseRedhatKernel
versionLinux:. 2.) It has got great
documentation to work on.
3.) Redhat
package manager is included to update the utilities or to delete the utilities.
4.)
Source Code is Included.
5.) Red
Hat is considered as the most secure Operating System
InterestinglyThFileSystemeverything
in UNIX is a file whether it be your keyboard, your terminal, your hard disk or
your Ram.
Here we will cover most of the details
of using the file system- what files are, how they are represented, directories
and file system hierarchy, permissions inodes and device files.
Basically
a file is a sequence of bytes. Magnetic tapes, mail messages, characters typed
on the keyboard, line printer output, data flowing in the pipes – each of these
is just a sequence of bytes as far as the system and the programs in it are
concerned.
The best way to know about files is to create a one by
yourself. There are several editors in Linux which you can use to create or to
edit the files. The most commonly used are PICO and VI.
We will be
working with the file systems in our next lecture.
YouLggingcanlogOnontotoa asystem:Linuxsystem
providing it your credentials. The credentials are your username and your
password. When you log onto the system your working directory becomes
/home/$Username where $Username is your user. You can work around with your
files and directories in your working directory. Working in your directory does
not
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hinder the functionality of the system
so you can play around with the system as and when you want.
EveryPermissions:filehas
a set of permissions associated with it, which determines what one can do with
the file. But there is a user superuser who
can do everything with any file.
There are three types of file permissions a file can have:
1.) Read permissions. (Denoted by r, numeric value=4)
2.) Write Permissions. (Denoted by w, numeric value = 2)
3.)
Executable Permissions. (Denoted by x, numeric value = 1)
Let us take an example of a file:
|
|||
-rwxrw-r--
|
test
|
day
|
testing
|
The above string –rw-rw-r- -indicates the permissions.
|
|||
You must note that there are
10 bits representing the permissions. The first bit tells that whether it is a
file or a directory. If the fist bit is d, it denotes a directory. In the above
case testing is a file. The second, third and the fourth bit denotes that there
are read,write and executable permissions to the owner of the file which in
this case is test. The fifth and sixth bit denotes that there are only read and
write permissions to the group to which this file belongs to which in this case
is day. The eighth bit denotes that others have only read permissions to the
file.
Make sure that only the owner of the file can change the permissions of
the file and no
|
||||
one else.
|
||||
So, the file is denoted by
|
Owner
|
group
|
Filename.
|
|
Permissions
string
|
||||
The
Directory hierarchy:
The
directory hierarchy in an orderly way starting from the top:
/bin
boot dev etc lib tmp unix usr
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Kochhar : kochhar77@yahoo.com
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These are
the main directories that are in the unix system.
Bin: (binaries) It is the basic
directory where the basic binary programs such as who and ed resides.
Dev: (devices) It is the directory where the device files
such as printers, harddisks etc are placed.
Etc:
(etcetera): It contains various administrative files such as the password
files. Lib: (library) It contains the parts and libraries of the C compiler.
Tmp: (temporaries): It is a repository
for short-lived files created during execution of the program.
Usr: (user):
It is called the “user File system”.
TheUsingShellthe-Stheell:programs that interprets your requests
to run programs- is the most important program for most UNIX users.
There are
mainly the following shells:
·
|
ash
|
/bin/sh
|
·
|
ash.static
|
/bin/ash.static
|
·
|
bash
|
/bin/bash
|
·
|
bash2
|
/bin/bash2
|
·
|
bsh
|
/bin/bsh
|
·
|
csh
|
/bin/csh
|
·
|
ksh
|
/bin/ksh
|
·
|
pdksh
|
/usr/bin/pdksh
|
·
|
rsh
|
/usr/bin/rsh
|
·
|
sh
|
/bin/sh
|
·
|
zsh
|
/bin/zsh
|
Introduction
to Some Commands:
Some commands with which you will feel working with the UNIX
system are as under:
These are the very basic implementation
of the commands for more options of the commands
: List the files and the directory.
Ls : displays who is logged in to the
machine.
Who :
Specifies the system date.
Date
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Kochhar : kochhar77@yahoo.com
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: echoes the typed matter onto the terminal. Echo:
sends mail to the specified sender.
Mail :
telnets you onto the specified machine. telnet:reads
and displays the file output.
Cat; word
count.
Wc :
change Mode Chmod : Change ownership. Chown:move
or rename the file. Mv : copy the file.
Cp: the text editor.
Vi : Change directory.
Cd :
Present working directory. Pwd : Make
directory.
Mkdir:
Creates the file with zero bytes. Touch:finds
a pattern in a particular file.
Grep: finds
a file or a directory in the unix system hierarchy. Find: finds
the difference between files.
Diff
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