Transcript Unix and shell programming

Unix and shell
programming - 15CS35
SEMESTER – III
04-08-2016
Syllabus and course outcomes
Link for syllabus
Operating system
 The operating system (OS) is the most important
program that runs on a computer.
 Every general-purpose computer must have an
operating system to run other programs
and applications.
 It is like a traffic cop -- it makes sure that different
programs and users running at the same time do not
interfere with each other.
 The operating system is also responsible for security, it
ensuring that unauthorized users do not access the
system.
Diagram
Classification of Operating systems
 Multi-user: Allows two or more users to run programs at
the same time. Some operating systems permit hundreds
or even thousands of concurrent users.
 Multiprocessing : Supports running a program on more
than one CPU.
 Multitasking : Allows more than one program to run
concurrently.
 Multithreading : Allows different parts of a single program
to run concurrently.
 Real time: Responds to input instantly.
overview
Operating systems provide
a software platform on top of which other
programs,
called application programs, can run
The application programs must be written
to run on top of a particular operating
system.
Interacting With the Operating System
 As a user, you normally interact with the operating system
through a set of commands.
 For example, the DOS operating system contains
commands such as COPY and RENAME for copying files and
changing the names of files, respectively
 The commands are accepted and executed by a part of
the operating system called thecommand processor or
command line interpreter.
 Graphical user interfaces allow you to enter commands by
pointing and clicking at objects that appear on the screen.
System
 A group of interdependent items that interact regularly
to perform a task.
 A computer system refers to the hardware and software
components that run a computer or computers.
 An information system is a system that collects and stores
data.
 System often simply refers to the operating system.
Operating system
Definition
An operating system (OS)
Is system software that manages computer
hardware and software resources and provides
common services for computer programs.
Application programs usually require an
operating system to function.
Types of operating systems
Single- and multi-tasking
A single-tasking system can only run one program at a time,
while a multi-tasking operating system allows more than one
program to be running in concurrency.
Single- and multi-user
Single-user operating systems have no facilities to
distinguish users, but may allow multiple programs to
run. A multi-user operating system extends the basic
concept of multi-tasking with facilities that identify
processes and resources
Continued…..
Distributed
A distributed operating system manages a group
of distinct computers and makes them appear to
be a single computer.
Embedded
Embedded operating systems are designed to be
used in embedded computer systems. They are
designed to operate on small machines
Clear picture on what we understood
Memory Management
 Memory management refers to management of Primary
Memory or Main Memory.
 Main memory is a large array of words or bytes where
each word or byte has its own address.
 Main memory provides a fast storage that can be
accessed directly by the CPU.
 For a program to be executed, it must in the main
memory.
 Allocates the memory and De-allocates the memory
Processor Management
In multiprogramming environment, the OS decides
which process gets the processor when and for
how much time.
This function is called process scheduling.
An operating system keep track of Keeps tracks of
processor and status of process.. Also it Allocates
and De-allocates
the processor (CPU) to a
process.
Device Management
 An Operating System manages device communication via
their respective drivers.
OS does:
 Keeps tracks of all devices. Program responsible for this task
is known as the I/O controller.
 Decides which process gets the device when and for how
much time.
 Allocates the device in the efficient way and De-allocates
devices.
File Management
A file system is normally organized into directories
for easy navigation and usage. These directories
may contain files and other directions.
OS does:
 Keeps track of information, location, uses, status etc. The
collective facilities are often known as file system.
 Decides who gets the resources.
 Allocates the resources.
 De-allocates the resources.
Other Important Activities of OS
 Security
 Control over system performance
 Job accounting
 Error detecting aids
 Coordination between other software's and users
Components of Unix System
 Unix Operating System has primarily three components
Kernel − Kernel is the core part of Linux. It is responsible for all major activities of
this operating system. It consists of various modules and it interacts directly with
the underlying hardware.
System Library − System libraries are special functions or programs using which
application programs or system utilities accesses Kernel's features.
System Utility − System Utility programs are responsible to do specialized,
individual level tasks.
What is Unix ?
 The UNIX operating system is a set of programs that act as a link
between the computer and the user.
 The computer programs that allocate the system resources and
coordinate all the details of the computer's internals is called the
operating system or kernel.
 Users communicates with the kernel through a program known as the
shell.
 The shell is a command line interpreter; it translates commands entered
by the user and converts them into a language that is understood by
the kernel.
 Unix was originally developed in 1969 by a group of AT&T employees at
Bell Labs, including Ken Thompson, Dennis Ritchie
Continued…
There are various Unix variants available in the
market. Solaris Unix, AIX, HP Unix and BSD are
few examples. Linux is also a flavor of Unix which
is freely available.
Several people can use a UNIX computer at the
same time; hence UNIX is called a multiuser
system.
A user can also run multiple programs at the
same time; hence UNIX is called multitasking.
Following are some of the important
features of Unix Operating System
Portable
Open Source
Multi-User
Multiprogramming
Hierarchical File System
Shell
Security
ARCHITECTURE
Unix Architecture
Components
Kernel: The kernel is the heart of the operating
system. It interacts with hardware and most of the
tasks like memory management, task scheduling and
file management.
Shell: The shell is the utility that processes your
requests. When you type in a command at your
terminal, the shell interprets the command and calls
the program that you want.
C Shell, Bourne Shell and Korn Shell are most famous
shells which are available with most of the Unix variants.
Continued…
 Commands and Utilities: There are various command
and utilities which you would use in your day to day
activities. cp, mv, cat and grep etc.
 Files and Directories: All data in UNIX is organized into
files. All files are organized into directories. These
directories are organized into a tree-like structure called
the file system.
Features
Main Features of UNIX
 This section contains a brief overview of the main features
of UNIX.
 multi-user
more than one user can use the machine at a time
supported via terminals (serial or network connection)
 multi-tasking, more than one program can be run at a
time
 hierarchical directory structure, to support the
organization and maintenance of files
 portability
Hierarchical File System
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Shells
What is a shell?
A command interpreter
“protects you from the kernel”
It really protects the kernel from you
FSU COP 4342 Unix Tools
Spring 2004
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Many Shells
Bourne shell (sh)
Creator Steve Bourne in the early 80’s
First shell Used for shell programming
C shell (csh)
Created at UCB their Unix implementation in the
early 80’s
Users wanted more familiar syntax
More features (for interactive uses) than sh (e.g.
job control and history)
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Many Shells
 Korn shell (ksh)
 Created by David Korn in the mid 80’s
 Compatible with sh but having most features of csh
 Features history editing (a.k.a. command-line editing)
 Was available on System V
 Public-domain version is pdksh
 T-shell (tcsh)
 has all csh features and less bugs
 Bourne-again shell (bash)
 Offered by FSF (free software foundation)
 Similar to ksh and csh
 Command-line editing
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What’s my shell?
Check your prompt
Usually bash uses $
Usually csh uses %
Usually tcsh uses >
Superuser “root” usually is #
UNIX Commands Structure
 To give a command to a UNIX system you type the name of the
command, along with any associated information, such as a filename,
and press the <Return> key.
 The typed line is called the command line
 UNIX uses a special program, called the shell or the command line
interpreter
The components of the command line are:
 the command;
 any options required by the command
 the command's arguments (if required).
For example, the general form of a UNIX command is:
 command [-option(s)] [argument(s)]
POSIX Single UNIX Specification
Unix Commands
 UNIX commands:
– Internal (builtin) and external command
 Some commands are internal, built into the shell.
 cd command is built-in. (the shell interprets that command and
changes your current directory).
 ls command is an external program stored in the file /bin/ls. • The
shell does not start a separate process to run internal commands.
 External commands require the shell to fork and exec a new sub
process; this takes some time, especially on a busy system.
 Check a command is internal or external: – $type cd – cd is a shell
builtin
Internal and External Commands
 Unix commands are grouped into two categories-Internal
and External.
Internal
 There is a set of commands which are part of the shell and
to execute them the shell does not need to search the
given path in the PATH variable.
 These are also called shell builtins or Internal Commands.
External
 Commands that are available as independently compiled
C programs usually located in the /bin or the /usr/bin
directory are called External Commands.
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Internal and External Commands
Internal commands
built into the shell
the shell performs the command
E.g. chdir or cd
External commands
Require the shell to fork and exec and a subprocess
will start
E.g. ls
FSU COP 4342 Unix Tools
Spring 2004
Continued…
Example:
 $ type ls
 ls is /bin/ls
 the above command returns the location or the path of the ls
command .Therefore ls is an external command.
 $ type echo
echo is a shell builtin
 the 'echo' command is an Internal Command or a shell builtin.
 $ type LS
LS: not found
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Summary on same…!!
Shell checks what type of command the user is
trying to run
Check if built-in
Else check if absolute path
Else check alias (except bash)
Check for executable in search path
Search path is a list of dir that the shell must check
An environment variable PATH lists these dir
 Look at an example
Search path is specified in the shell start up files
System Boot-up
 If you have a computer which has UNIX operating
system installed on it, then you simply need to turn on its
power to make it live.
 As soon as you turn on the power, system starts booting
up and finally it prompts you to log into the system,
which is an activity to log into the system and use it for
your day to day activities.
Login Unix
To log in
 Have your userid (user identification) and password ready.
Contact your system administrator if you don't have these yet.
 Type your userid at the login prompt, then press ENTER. Your userid
is case-sensitive, so be sure you type it exactly as your system
administrator instructed.
 Type your password at the password prompt, then press ENTER.
Your password is also case-sensitive.
 If you provided correct userid and password then you would be
allowed to enter into the system. Read the information and
messages that come up on the screen something as below.
UI
to check calendar you need to type
cal command as follows −
Change Password
 All Unix systems require passwords to help ensure that
your files and data remain your own and that the system
itself is secure from hackers and crackers.
Here are the steps to change your password −
 To start, type passwd at command prompt as shown
below.
 Enter your old password the one you're currently using.
 Type in your new password. Always keep your password
complex enough so that no body can guess it. But make
sure, you remember it.
 You would need to verify the password by typing it
again.
UI
Listing Directories and Files
All data in UNIX is organized into files.
All files are organized into directories.
These directories are organized into a tree-like
structure called the file system
You can use ls command to list out all the files
Following is the example of using ls command
with -l option.
UI
Who Are You?
 While you're logged in to the system, you might be
willing to know : Who am I?
 The easiest way to find out "who you are" is to enter the
who am i command −
Who is Logged In?
 Sometime you might be interested to know who is logged in to the
computer at the same time.
 There are three commands are available to get you this
information, based on how much you'd like to learn about the other
users: users, who, and w.
Logging Out
When you finish your session, you need to log
out of the system to ensure that nobody else
accesses your files while masquerading as you.
just type logout command at command
prompt, and the system will clean up everything
and break the connection
System Shutdown
Flexibility in using commands
$Wc note; ls –l note
Command line can overflow
$echo “ this is
>a three line
>text message”
o/p
This is
A three line
Text message
To break – press ctrl+z
When things go wrong
 Terminal and keyboard have no uniform behaviroul
pattern
 Backspacing will not work all time
 Wen you use backspace u can see ^H^H
 Ctrl+h or delete hey
Killing a line
 Ctrl+u
Break by
Ctrl+d
Ctrl+z
Knowing the user terminal
 About tty
 Print the file name of the terminal connected to
standard input.
tty syntax
 tty [OPTION]...
Options
 -s, --silent, --quiet Print nothing, only return an exit
status.
 --help display this help and exit.
 --version output version information and exit.
Continued….
tty examples
$tty
Running tty by itself will display the current tty
session as shown below:
/dev/pts/0
stty
About stty
$Stty
changes and prints terminal line settings.
Description
stty displays or changes the characteristics of
the terminal.
displaying its characteristics and setting
characteristics
Root
 root is the user name or account that by default has access to all
commands and files on a Linux or other Unix-like operating system.
 The root directory, which is the top level directory on a system That is, it is
the directory in which all other directories, including their subdirectories
and files reside. The root directory is designated by a forward slash ( / ).
 Root privileges are the powers that the root account has on the system.
 root's powers are the ability to modify the system in any way desired and to
grant and revoke access permissions
 Login in terminal
Su: Acquiring superuser status
$su
Password:******
#pwd
/home/sh
Prompt changes but directory dosen’t
From super user access we can switch to other user by using
$su – username
Without password
Administrators Privileges
 Change the contents or attributes of any file like its
permissions and ownerships
 He can delete the file even if the directory is write
protected
 Initiate or kill any process
 Change any user password without knowing the existing
one
 Set system clock with date
 Address all users concurrently ----- wall
 Limit the file size fir each users
 Control overall access with FTP as well.
Date setting
Wall : communicating with users
 It address all users simultaneously
#wall
 Welcome all for the day 3 session
All the user who are currently logged in will this message
 Ulimit
Restricts the size
As super user we can also modify the same.
Continued…
user management
Creating the user involves the following parameters
 UID and user Name
 GID and group name
 The home directory
 The login shell
 Mailbox in var/mail
 The password
----------------------------------------------------- Most of these are found in single line identifying the user
in /etc/passwd
useradd and usermod , userdel
 Adds the new user to the system
 All parameters related to the user should be provided in command
line
 Example:
#useradd –u 210 –g dba –c “the rdbms” –d /home/oracle –s /bin/ksh –
m oracle
Usermod and userdel
#usermod
#userdel
/etc/passwd and /etc/shadow
All user information except the password
encryption is now stored in /etc/passwd
The encryption itself is stored in
/etc/shadow
Discussions
Thank you