Os Lab Manual

Network-OS Lab Manual

LINUX - THE OS

Linux is a Unix-like computer operating system. Linux is one of the most prominent

examples of free software and open source development; its underlying source code can be

modified, used, and redistributed by anyone, freely.

The Linux kernel was first released to the public on 17 September 1991, for the Intel

x86 PC architecture. The kernel was augmented with system utilities and libraries from the

GNU project to create a usable operating system, which later led to the alternate term

GNU/Linux.Linux is now packaged for different uses in Linux distributions, which contain

the kernel along with a variety of other software packages tailored to requirements.

Predominantly known for its use in servers, Linux has gained the support of

corporations such as IBM, Sun Microsystems, Hewlett-Packard, and Novell, and is used as

an operating system for a wide variety of computer hardware, including desktop computers,

supercomputers, and embedded devices such as mobile phones and routers.

The Unix operating system was conceived and implemented in the 1960s and first

released in 1970. Its wide availability and portability meant that it was widely adopted,

copied and modified by academic institutions and businesses, with its design being

influential on authors of other systems.

A 2001 study of Red Hat Linux 7.1 found that this distribution contained 30 million

source lines of code. Using the Constructive Cost Model, the study estimated that this

distribution required about eight thousand man-years of development time. According to the

study, if all this software had been developed by conventional proprietary means, it would

have cost about 1.08 billion dollars (year 2000 U.S. dollars) to develop in the United States.

Most of the code (71%) was written in the C programming language, but many other

languages were used, including C++, Lisp, assembly language, Perl, Fortran, Python and

Department Of Computer Science BM II College Of Engineering, Sasthamcotta1

http://en.wikipedia.org/wiki/Python_(programming_language)

http://en.wikipedia.org/wiki/Fortran

http://en.wikipedia.org/wiki/Perl

http://en.wikipedia.org/wiki/Assembly_language

http://en.wikipedia.org/wiki/Lisp_(programming_language)

http://en.wikipedia.org/wiki/C++

http://en.wikipedia.org/wiki/Programming_language

http://en.wikipedia.org/wiki/Computer_programming

http://en.wikipedia.org/wiki/C_(programming_language)

http://en.wikipedia.org/wiki/Proprietary_software

http://en.wikipedia.org/wiki/COCOMO

http://en.wikipedia.org/wiki/Source_lines_of_code

http://en.wikipedia.org/wiki/Red_Hat_Linux

http://en.wikipedia.org/wiki/Unix

http://en.wikipedia.org/wiki/Routers

http://en.wikipedia.org/wiki/Mobile_phone

http://en.wikipedia.org/wiki/Embedded_devices

http://en.wikipedia.org/wiki/Supercomputers

http://en.wikipedia.org/wiki/Desktop_computer

http://en.wikipedia.org/wiki/Hardware

http://en.wikipedia.org/wiki/Novell

http://en.wikipedia.org/wiki/Hewlett-Packard

http://en.wikipedia.org/wiki/Sun_Microsystems

http://en.wikipedia.org/wiki/IBM

http://en.wikipedia.org/wiki/Server_(computing)

http://en.wikipedia.org/wiki/Linux_distribution

http://en.wikipedia.org/wiki/GNU

http://en.wikipedia.org/wiki/Library_(computer_science)

http://en.wikipedia.org/wiki/System_utility

http://en.wikipedia.org/wiki/Intel_x86

http://en.wikipedia.org/wiki/Intel_x86

http://en.wikipedia.org/wiki/1991

http://en.wikipedia.org/wiki/September_17

http://en.wikipedia.org/wiki/Linux_kernel

http://en.wikipedia.org/wiki/Source_code

http://en.wikipedia.org/wiki/Open_source

http://en.wikipedia.org/wiki/Free_software

http://en.wikipedia.org/wiki/Operating_system

http://en.wikipedia.org/wiki/Unix-like


various shell scripting languages. Slightly over half of all lines of code were licensed under

the GPL. The Linux kernel itself was 2.4 million lines of code, or 8% of the total

Programming on Linux

Most Linux distributions support dozens of programming languages. Core system

software such as libraries and basic utilities are usually written in C. Enterprise software is

often written in C, C++, Java, Perl, Ruby, or Python. The most common collection of utilities

for building both Linux applications and operating system programs is found within the GNU

toolchain, which includes the GNU Compiler Collection (GCC) and the GNU build system.

Amongst others, GCC provides compilers for C, C++, Java, and Fortran. The Linux kernel

itself is written to be compiled with GCC.

Most also include support for Perl, Ruby, Python and other dynamic languages.

Examples of languages that are less common, but still well-supported, are C# via the Mono

project, and Scheme. A number of Java Virtual Machines and development kits run on

Linux, including the original Sun Microsystems JVM (HotSpot), and IBM's J2SE RE, as well

as many open-source projects like Kaffe. The two main frameworks for developing graphical

applications are those of GNOME and KDE. These projects are based on the GTK+ and Qt

widget toolkits, respectively, which can also be used independently of the larger framework.

Both support a wide variety of languages. There are a number of Integrated development

environments available including Anjuta, Eclipse, KDevelop, MonoDevelop, NetBeans, and

Omnis Studio while the traditional editors Vim and Emacs remain popular.

Although free and open source compilers and tools are widely used under Linux,

there are also proprietary solutions available from a range of companies, including the Intel

C++ Compiler, PathScale, Micro Focus COBOL, Franz Inc, and the Portland Group.

We use here, vi editor for all entering and editing purposes. The commands used

in vi editors are….


http://en.wikipedia.org/wiki/Franz_Inc

http://en.wikipedia.org/wiki/Intel_C++_Compiler

http://en.wikipedia.org/wiki/Intel_C++_Compiler

http://en.wikipedia.org/wiki/Emacs

http://en.wikipedia.org/wiki/Vim_(text_editor)

http://en.wikipedia.org/wiki/Omnis_Studio

http://en.wikipedia.org/wiki/NetBeans

http://en.wikipedia.org/wiki/MonoDevelop

http://en.wikipedia.org/wiki/KDevelop

http://en.wikipedia.org/wiki/Eclipse_(computing)

http://en.wikipedia.org/wiki/Anjuta

http://en.wikipedia.org/wiki/Integrated_development_environment

http://en.wikipedia.org/wiki/Integrated_development_environment

http://en.wikipedia.org/wiki/Widget_toolkit

http://en.wikipedia.org/wiki/Qt_(toolkit)

http://en.wikipedia.org/wiki/GTK+

http://en.wikipedia.org/wiki/KDE

http://en.wikipedia.org/wiki/GNOME

http://en.wikipedia.org/wiki/Kaffe

http://en.wikipedia.org/wiki/HotSpot

http://en.wikipedia.org/wiki/Java_Virtual_Machine

http://en.wikipedia.org/wiki/Scheme_programming_language

http://en.wikipedia.org/wiki/Mono_(software)

http://en.wikipedia.org/wiki/C_Sharp

http://en.wikipedia.org/wiki/Python_programming_language

http://en.wikipedia.org/wiki/Ruby_programming_language

http://en.wikipedia.org/wiki/Perl

http://en.wikipedia.org/wiki/Fortran

http://en.wikipedia.org/wiki/Java_(programming_language)

http://en.wikipedia.org/wiki/C++

http://en.wikipedia.org/wiki/C_(programming_language)

http://en.wikipedia.org/wiki/GNU_build_system

http://en.wikipedia.org/wiki/GNU_Compiler_Collection

http://en.wikipedia.org/wiki/GNU_toolchain

http://en.wikipedia.org/wiki/GNU_toolchain

http://en.wikipedia.org/wiki/Programming_language

http://en.wikipedia.org/wiki/Shell_script


To Start

To use vi on a file type in vi filename. If the file named filename exist, then it

wthe file will be displayed,otherwise an empty file and screen are created into which you

may enter the text.

vi filename –edit filename startng at line 1

vi –r filename recover filename that was being edited when system crashed.

To Exit vi

Usually the new or modified filename is saved when you leave vi. However it also

possible to quit without saving the file.

:x<return> - quit vi, writing out modified file named in original invocation.

:wq<return> - quit vi, writing out the modified file to file named in original invocation.

:q< return> -quit(or exit) vi.

: q!<return> -quit vi even though latest cvhanges have not been saved for this vi call.

Moving the cursor

The symbol ^ shown below , before a letter means that the <ctrl>key should be

held down while the letter is pressed.

J or ,return>{or down arrow] - move the cursor down one line.

K[or up-arrow] - move the cursor up one line.

H or <Backspace>[or left arrow] –move cursor left one character.

L or <space>[or right arrow] -move cursor right one character.

0(zero) -move cursor to start of the current line.

$ -move cursor to end of current line.

w –move cursor to the beginning of the next word.

B -move the cursor back to beginning of the preceeding word.

:0<return>or 1G -move the cursor to first line in file.

:n<return> or nG -move the cursor to line n.

:$<return> or G -move cursor to last of the line.



Screen Manipulation

The following commands allow the vi editor screen(or window) to move up or

down several lines and to be refreshed.

^f -move forward one screen.

^b –move backward one screen.

^d –move down(forward) one half screen.

^u –move up(back) one half screen.

^l – redraws the screen removing the deleted lines.

Inserting or Adding Text

The following commands allow you to insert and add text. Each of these

commands puts the vi editor into insert mode; thus the >Esc> key must be pressed to

terminate the entry of thetext and to put the vi editor back into command mode.

i - insert text before cursor, until<Esc> hit.

I - insert text at begginning of current line, until<Esc> hit.

a – append text after cursor, until <Esc> hit.

A –append text to end of the current line,until<Esc> hit.

o –open and put text in a new line below current line, until<Esc>hit.

O –open and put text in anew line above current line, until <Esc> hit.

Deleting Text

The following commands allow you to delete text.

x- delete single character under cursor.

Nx –delete N characters, starting with character under cursor.

dw – delete the single word beginning with the character under cursor.

dNw – delete N words beginning with the character under cursor.

D – delete the remainder of line,starting with current cursor position.

dd –delete entire curent line.

Ndd or dNd –delete N lines beginning with the curent line.



Cutting and Pasting Text

The following commands allow you to copy and paste text.

yy - copy(yank,cut)the curent line into buffer.

Nyy or yNy –copy(yank,cut) the next N lines, including the curent line, into the buffer.

p –put(paste) the line(s) in the buffer into the text after the current line.

Searching Text

A common occurences in text editing is to replace one word or phrase by

another.To locate instances of particular sets of characters(or strings), use the following

commands.

/string –search forward for occurrence of string in text.

?string –search back ward for occurences of string in text.

n –move to next occurrence of search string.

N –move the next occurence of search string in opposite direction.

Saving and Reading Files

These commands permit you to input and output files other than the named file

with which you are currently working.

:r filename<return> -read file named filename and insert after current line.

:w<return> -write current contents to file named in original vi call.

:w newfile<return> -write current contents to a new file bnamed newfile.

:12,35w smallfile<return> -write the contents of the lines numbered 12 through 35 to a new

file named smallfile.

:w! prevfile<return> - write curent contents over a pre-existing file named prevfile.

GCC Commands

gcc programname.c –This compile and link the program and a.out file is created . This can be

executed by ./a.out .

gcc –o outputprogramname programname.c- This compile and link the programand a.out file

is created. This can be executed by outputprogramname.

gcc –o outputprogramname programname.c-lpthread – To compile with threads



THREAD

Theory

Multiple strands of execution in a single program are called threads or thread is a

sequences of control within a process.Thread proces include thread creation, termination,

synchronization (joins,blocking), scheduling and process interaction.All threads within a

process share the same addresss space.

A thread in computer science is short for a thread of execution. Threads are a way

for a program to fork (or split) itself into two or more simultaneously (or pseudo-

simultaneously) running tasks. Threads and processes differ from one operating system to

another, but in general, the way that a thread is created and shares its resources is different

from the way a process does.

Multiple threads can be executed in parallel on many computer systems. This

multithreading generally occurs by time slicing, wherein a single processor switches between

different threads, in which case the processing is not literally simultaneous, for the single

processor is only really doing one thing at a time. This switching can happen so fast as to

give the illusion of simultaneity to an end user.

Threads are distinguished from traditional multi-tasking operating system processes in

that processes are typically independent, carry considerable state information, have separate

address spaces, and interact only through system-provided inter-process communication

mechanisms. Multiple threads, on the other hand, typically share the state information of a

single process, and share memory and other resources directly. Context switching between

threads in the same process is typically faster than context switching between processes.

Systems like Windows NT and OS/2 are said to have "cheap" threads and "expensive"

processes; in other operating systems there is not so great a difference.


http://en.wikipedia.org/wiki/OS/2

http://en.wikipedia.org/wiki/Windows_NT

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http://en.wikipedia.org/wiki/Resource_(computer_science)

http://en.wikipedia.org/wiki/Computer_storage

http://en.wikipedia.org/wiki/Inter-process_communication

http://en.wikipedia.org/wiki/Address_space

http://en.wikipedia.org/wiki/State_(computer_science)

http://en.wikipedia.org/wiki/Computer_process

http://en.wikipedia.org/wiki/Context_switch

http://en.wikipedia.org/wiki/Central_processing_unit

http://en.wikipedia.org/wiki/Computer_multitasking

http://en.wikipedia.org/wiki/Process_(computing)



http://en.wikipedia.org/wiki/Task_(computers)

http://en.wikipedia.org/wiki/Fork_(operating_system)

http://en.wikipedia.org/wiki/Computer_program

http://en.wikipedia.org/wiki/Computer_science


Thread Basics

Thread operations include thread creation, termination, synchronization

(joins,blocking), scheduling, data management and process interaction.

A thread does not maintain a list of created threads, nor does it know the thread that

created it.

All threads within a process share the same address space.

Threads in the same process share:

o Process instructions

o Most data

o open files (descriptors)

o signals and signal handlers

o current working directory

o User and group id

Each thread has a unique:

o Thread ID

o set of registers, stack pointer

o stack for local variables, return addresses

o signal mask

o priority

o Return value: errno

pthread functions return "0" if OK.

Thread Creation

Function call : pthread_create

int pthread_create(pthread_t*thread,pthread_attr_t*attr,void *(*start_routine)

(void*),void *arg);

Arguments

->thread - returns the thread id.(unsigned long int defined in bits/pthreadtypes.h)



->attr-Set to NULL if default thread attributes are used.(else define members of the struct

pthread_attr_t defined in bits/pthreadtypes.h). Attributes include:

detached state(joinable? Default: PTHREAD_CREATE_JOINABLE.Other

option:PTHREAD_CREATE_DETACHED)

schedulingpolicy(realtime?

PTHREAD_INHERIT_SCHED,PTHREAD_EXPLICIT_SCHED,SCHED_OTHER)

scheduling parameter

inheritsched attribute(Default:PTHREAD_EXPLICIT_SCHED,inherit from parent

thread:PTHREAD_INHERIT_SCHED)

scope(Kernelthreads:PTHREAD_SCOPE_SYSTEM user threads

PTHREAD_SCOPE_PROCESS, pick one or the other not both)

guard size

stack address

stack size(default minimum PTHREAD_STACK_SIZE set in pthread.h)

->void *(start_routine)-pointer to the function to be threaded.Function has a single

argument:pointer to void.

->*arg-pointer to argument of function. To pass multiple arguments,sent a pointer to the

structure.

Termination Of Thread

Function call: pthread_exit

void pthread_exit(void *retval);

Arguments

retval – return value of the thread.

This routine kills the thread.The pthread _exit never returns. If the thread is not detached the

thread id and return value may be examined from another thread by using pthread_join.

Thread Synchronization

The thread libraries provide three synchronization mechanisms

mutexes – Mutual exclusion lock: Block access to variable by other threads. This

enforces exclusive access by thread to a variable or set of variables.



joins–Make athread wait till others are complete(terminated).

conditions variables- data type pthread_cond_t.

Benefits of Threads vs Processes

If implemented correctly then threads have some advantages of (multi) processes, They take:

Less time to create a new thread than a process, because the newly created thread uses

the current process address space.

Less time to terminate a thread than a process.

Less time to switch between two threads within the same process, partly because the

newly created thread uses the current process address space.

Less communication overheads -- communicating between the threads of one process

is simple because the threads share everything: address space, in particular. So, data

produced by one thread is immediately available to all the other threads.

POSIX Threads is a POSIX standard for threads. The standard defines an API for

creating and manipulating threads.

Libraries implementing the POSIX Threads standard are often named Pthreads.

Pthreads are most commonly used on POSIX systems such as Linux and Unix,

Algorithm

1. Start.

2. Provide function prototype and definition for the function that is used as thread.

3. Declare variables for storing the thread id and thread attributes.

4. Initialise the thread attributes.

5. Create the thread.

6. Call the thread for execution.

7. Wait for the thread to execute.

8. Stop.



http://en.wikipedia.org/wiki/Linux

http://en.wikipedia.org/wiki/Application_programming_interface

http://en.wikipedia.org/wiki/Thread_(computer_science)

http://en.wikipedia.org/wiki/POSIX


Program

/*Program for the creation of simple thread created in a non detached manner.

* This program illustrates the manner in which a thread can be created from within

the main() function.

* This program creates a thread called 'add' which accepts two integer values from

the user and prints the sum of it.

* NOTE:->This program should be compiled using the command 'cc

simplethread.c -lpthread' and executed using './a.out'.

*/

//inculsion part

#include<stdio.h>

#include<pthread.h>

void* add(void*); //prototype of the thread function.

int main() //main function (return type should be int in linux).

{

int error; //variable to check error (optional)

pthread_t thread_id; //variable to store thread id.

pthread_attr_t thread_attribute; //variable to store properties of thread.

pthread_attr_init(&thread_attribute); //function call for setting the default properties.

error=pthread_create(&thread_id,&thread_attribute,add,NULL); //function for thread

creation.

//error checking (optional)

if(error!=0)

{

printf("\nError in thread creation.\n");

exit(0);

}

error=pthread_join(thread_id,NULL); //function for thread calling.

//error checking (optional)

if(error!=0)



{ printf("\nError in thread joining.\n");

exit(0);

}

} //function definition for the thread function.

void * add(void *args)

{ int a,b;

printf("\nEnter the first number.\n");

scanf("%d",&a);

printf("\nEnter the second number.\n");

scanf("%d",&b);

printf("\nThe sum is:\t%d\n",a+b);

}

Output

MULTIPLE THREAD



Algorithm

1. Start.

2. Provide function prototype and definition for the function that has to be used as thread.

3. Declare the variables for storing the thread id and thread attributes as required

depending on the no: of threads to be created.

4. Initialize the thread attribute variables to their default values.

5. Set detach property of the thread.

6. Create the threads as required.

7. Wait for the thread to execute.

8. Stop.

Program

//Inculsion part.

#include<stdio.h>#include<pthread.h>

//function prototype.void * add(void *);

//Variable to count the executed thread.int end;

//main function.int main(){ pthread_t tid1,tid2; pthread_attr_t attribute;

pthread_attr_init(&attribute); //function to set detach property of the thread.

pthread_attr_setdetachstate(&attribute,PTHREAD_CREATE_DETACHED);

pthread_create(&tid1,&attribute,add,(void *)1); pthread_create(&tid2,&attribute,add,(void*)2);

//to wait for the thread to finish execution. while(end<2) { }



}

//function prototype for the thread function.void * add(void * args){ int a,b; printf("\nEntered into %d thread\n",args); printf("\nEnter the first number for thread %d\n",args); scanf("%d",&a);

printf("\nEnter the second number for thread %d\n",args); scanf("%d",&b);

printf("The sum computed by thread %d:\t%d\n",args,a+b); end++;}

Output

DYNAMIC MULTITHREAD CREATION



Algorithm

1. Start.

2. Provide the function prototype and definition for the function that

has to be used as thread.

3. Declare variables to store the thread id and thread attributes.

4. Accept the no. of threads from the user.

5. Create the threads by suitably initialising the thread variables.

6. Wait until the threads execute.

7. Stop.

Program

/*Program to describe dynamic multiple thread creation and passing arguments to it.

* This program illustrates the steps involved in creating multiple threads dynamically.

* This program accepts the number of threads from the user and creates it at run time.

* The procedure is similar to that we used to create multiple threads.

NOTE:->This module can be compiled using the command 'cc dynamic multithread creation.c -lpthread' and executed using './a.out'

//inculsion.#include<stdio.h>#include<pthread.h>

//function prototype.void * thread_function(void *args[]);

//variable to know the end of threads execution.int end;int main(){ int i,count,j;



int args[2];

pthread_attr_t attribute; pthread_t tid;

pthread_attr_init(&attribute); pthread_attr_setdetachstate(&attribute,PTHREAD_CREATE_DETACHED);

//for accepting the number of threads to be created. printf("\nEnter the number of threads.\n"); scanf("%d",&count); for(i=0,j=count;i<count;i++,j--) {

//inserting the arguments for the thread args[0]=i+1; args[1]=j;

printf("\n\t\tCreating thread %d.\n",i+1);

pthread_create(&tid,&attribute,(void *)thread_function,(void *)args); printf("\n\t\tCreated thread %d\n",i+1); sleep(1); }

//waiting for the thread execution. while(end!=count) { }}

//function definition.void * thread_function(void *args[]){ int a,b;

a=(int)args[0]; b=(int)args[1]; printf("\n\t\tEntered into %d thread.\n",a);

printf("\nFirst value obtained from main function:\t%d\n",a); printf("\nSecond value obtained from main function:\t%d\n",b); end++;}



Output

SEMAPHORE



Theory

Semaphores are a programming construct designed by E. W. Dijkstra in the late

1960s. Dijkstra's model was the operation of railroads: consider a stretch of railroad in which

there is a single track over which only one train at a time is allowed. Guarding this track is a

semaphore. A train must wait before entering the single track until the semaphore is in a state

that permits travel. When the train enters the track, the semaphore changes state to prevent

other trains from entering the track. A train that is leaving this section of track must again

change the state of the semaphore to allow another train to enter. In the computer version, a

semaphore appears to be a simple integer. A process (or a thread) waits for permission to

proceed by waiting for the integer to become 0. The signal if it proceeds signals that this by

performing incrementing the integer by 1. When it is finished, the process changes the

semaphore's value by subtracting one from it.

Semaphore is a variable that can take only the values 0 and 1, binary semaphore. This

is the most common form. Semaphore that can take many positive values are called general

semaphores.

The definition of P and V are surprisingly simple. Suppose we have semaphore

variable sv. The two operations are defined as follows:

P(sv) – If sv is greater than zero, decrement sv, if sv is zero, suspend execution of this

process.

V(sv) – If some other process has been suspend waiting for sv, make it resume execution. If

no process is suspended waiting for sv, Increment sv.

Semaphores let processes query or alter status information. They are often used to

monitor and control the availability of system resources such as shared memory segments.

POSIX semaphores are much lighter weight than are System V semaphores. A

POSIX semaphore structure defines a single semaphore, not an array of up to twenty five

semaphores. The POSIX semaphore functions are:

sem_open() -- Connects to, and optionally creates, a named semaphore



sem_init() -- Initializes a semaphore structure (internal to the calling program, so not a

named semaphore).

sem_close() -- Ends the connection to an open semaphore.

sem_unlink() -- Ends the connection to an open semaphore and causes the semaphore to be

removed when the last process closes it.

sem_destroy() -- Initializes a semaphore structure (internal to the calling program, so not a

named semaphore).

sem_getvalue() -- Copies the value of the semaphore into the specified integer.

sem_wait(), sem_trywait() -- Blocks while the semaphore is held by other processes or

returns an error if the semaphore is held by another process.

sem_post() -- Increments the count of the semaphore.

All POSIX semaphore functions and types are prototyped or defined in semaphore.h.

To define a semaphore object, use

sem_t sem_name;

To initialize a semaphore, use sem_init():

int sem_init(sem_t *sem, int pshared, unsigned int value);

sem points to a semaphore object to initialize

pshared is a flag indicating whether or not the semaphore should be shared with

fork()ed processes. LinuxThreads does not currently support shared semaphores

value is an initial value to set the semaphore to

Example of use:

sem_init(&sem_name, 0, 10);



To wait on a semaphore, use sem_wait:

int sem_wait(sem_t *sem);

Example of use:

sem_wait(&sem_name);

If the value of the semaphore is negative, the calling process blocks; one of the

blocked processes wakes up when another process calls sem_post.

To increment the value of a semaphore, use sem_post:

int sem_post(sem_t *sem);

Example of use:

sem_post(&sem_name);

It increments the value of the semaphore and wakes up a blocked process waiting on

the semaphore, if any.

To find out the value of a semaphore, use

int sem_getvalue(sem_t *sem, int *valp);

gets the current value of sem and places it in the location pointed to by valp

Example of use:

int value;

sem_getvalue(&sem_name, &value);

printf("The value of the semaphors is %d\n", value);

To destroy a semaphore, use

int sem_destroy(sem_t *sem);



destroys the semaphore; no threads should be waiting on the semaphore if its

destruction is to succeed.

Example of use:

sem_destroy(&sem_name);

Using semaphores - a short example

Consider the problem we had before and now let us use semaphores: Declare the semaphore global (outside of any funcion):

sem_t mutex;

Initialize the semaphore in the main function: sem_init(&mutex, 0, 1);

Thread 1 Thread 2 data

sem_wait (&mutex); --- 0

--- sem_wait (&mutex); 0

a = data; /* blocked */ 0

a = a+1; /* blocked */ 0

data = a; /* blocked */ 1

sem_post (&mutex); /* blocked */ 1

/* blocked */ b = data; 1

/* blocked */ b = b + 1; 1

/* blocked */ data = b; 2

/* blocked */ sem_post (&mutex); 2

[data is fine. The data race is gone.]

The basic operation of these functions is essence the same as described above, except

note there are more specialised functions, here.

Program

/* Program to demonstrate the usage of semaphore variable in controlling the access to specific resources.



* This program contains two functions which display their own messages.

* The display is suitably controlled by the use of semaphore variable.

* It is a program in which a semaphore variable is shared between the main function and a thread function.

* This module can be compiled using 'cc semaphore1.c -lpthread' and executed './a.out'

//inculsion part. #include<stdio.h>#include<pthread.h>#include<semaphore.h>

//function prototype for the thread function.void * display_function();

//global semaphore variable to be shared.sem_t sem_var;

int main(){ pthread_t tid; pthread_attr_t attr; int i;//initialising the semaphore variable with an initial value 0 (third arguement.) sem_init(&sem_var,0,0);

pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);

pthread_create(&tid,&attr,display_function,NULL);

for(i=0;i<5;i++) { printf("\n Displaying from the main function:\t%d\n",i+1);

//waiting for the resources. sem_wait(&sem_var); }

//destroying the semaphore variable. sem_destroy(&sem_var);}

void * display_function()



{ int i; for(i=0;i<5;i++) { printf("\n***** Displaying from the thread function.:\t%d\n",i+1);

//releasing resources. sem_post(&sem_var); sleep(1); }}

Output

SERIALISABILITY PROBLEM. (By using Semaphore Variable)

Program



* This program uses a variable 'data' whose value is used by two thread function.

* But the condition is that when a function uses it no other function should use it.

* This problem is tackled by definig two thread function and suitably making them access

it by the use of semaphore variable.

* This module can be compiled using 'cc semaphore2.c -lpthread' and executed './a.out'

//inculsion part.#include<stdio.h>#include<pthread.h>#include<semaphore.h>

//prototype for thread functions.void * thread_function1();void * thread_function2();

//global variables.int data=0,end=0;

//global semaphore variables.sem_t sem_var;

int main(){ pthread_t t1,t2; pthread_attr_t attr;

pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED);

sem_init(&sem_var,0,1);

pthread_create(&t1,&attr,thread_function1,NULL); pthread_create(&t2,&attr,thread_function2,NULL);

while(end!=2) { }

printf("\n\t****** The value of DATA is:\t%d ******\n",data);}

//definition of first thread function.void * thread_function1(){ int a;

printf("\nEntered into thread function:1\n");



printf("\nThread function:1 waiting to gain access\n");

sleep(1); sem_wait(&sem_var); printf("\nAccess gained by thread function:1\n");

printf("\nThread function:1 using the value of 'DATA' \n");

a=data; a=a+1; data=a;

sem_post(&sem_var); printf("\nResources released by thread function:1\n"); end++;}

//definition of second thread function.void * thread_function2(){ int b;

printf("\nEntered into thread function:2\n"); printf("\nThread function:2 waiting to gain access\n");

sleep(1); sem_wait(&sem_var); printf("\nAccess gained by thread function:2\n"); printf("\nThread function:2 using the value of 'DATA' \n"); b=data; b=b+1; data=b;

sem_post(&sem_var); printf("\nResources released by thread function:2\n"); end++;}

Output



DINING PHILOSOPHER’S PROBLEM



The problem

The dining philosophers problem is summarized as five philosophers sitting at a table

doing one of two things - eating or thinking. While eating, they are not thinking, and while

thinking, they are not eating. The five philosophers sit at a circular table with a large bowl of

spaghetti in the center. A fork is placed in between each philosopher, and as such, each

philosopher has one fork to his or her left and one fork to his or her right. As spaghetti is

difficult to serve and eat with a single fork, it must be assumed that in order for a philosopher

to eat, the philosopher must have two forks. In the case of the dining philosopher, the

philosopher can only use the fork on his or her left or right.

Illustration of the dining philosophers problem

In some cases, the dining philosophers problem is explained using rice and chopsticks

as opposed to spaghetti and forks, as it is generally easier to understand that two chopsticks

are required, whereas one could arguably eat spaghetti using a single fork, or using a fork and

a spoon. In either case, only one instrument (fork or chopstick) can be picked up at a time,

and the philosopher must have two instruments in order to eat.


http://en.wikipedia.org/wiki/Image:Dining_philosophers.png

http://en.wikipedia.org/wiki/Image:Dining_philosophers.png


The philosophers never speak to each other, which creates a dangerous possibility of

deadlock in which every philosopher holds a left fork and waits perpetually for a right fork

(or vice versa).

Originally used as a means of illustrating the problem of deadlock, this system

reaches deadlock when there is a 'cycle of ungranted requests'. In this case philosopher P1

waits for the fork grabbed by philosopher P2 who is waiting for the fork of philosopher P3

and so forth, making a circular chain.

Starvation (and the pun was intended in the original problem description) might also

occur independently of deadlock if a philosopher is unable to acquire both forks due to a

timing issue. For example there might be a rule that the philosophers put down a fork after

waiting five minutes for the other fork to become available and wait a further five minutes

before making their next attempt. This scheme eliminates the possibility of deadlock (the

system can always advance to a different state) but still suffers from the problem of livelock.

If all five philosophers appear in the dining room at exactly the same time and each picks up

their left fork at the same time the philosophers will wait five minutes until they all put their

forks down and then wait a further five minutes before they all pick them up again.

The lack of available forks is an analogy to the locking of shared resources in real

computer programming, a situation known as concurrency. Locking a resource is a common

technique to ensure the resource is accessed by only one program or chunk of code at a time.

When the resource the program is interested in is already locked by another one, the program

waits until it is unlocked. When several programs are involved in locking resources, deadlock

might happen, depending on the circumstances. For example, one program needs two files to


http://en.wikipedia.org/wiki/Concurrent_programming

http://en.wikipedia.org/wiki/Deadlock#Livelock

http://en.wikipedia.org/wiki/Resource_starvation

http://en.wikipedia.org/wiki/Deadlock

http://en.wikipedia.org/wiki/Image:Dining_philosophers.gif


process. When two such programs lock one file each, both programs wait for the other one to

unlock the other file, which will never happen.

Algorithm

* The algorithm for the process is..........

1.Start.

2.Initialise the thread variables as required.

3.Create the threads representing philosophers.

4.Wait until the threads finishes execution.

5.Stop.

The algorithm for the philosopher is as..........

1.Start.

2.Wait for the left fork/spoon.

3.Wait for the right fork/spoon.

4.Start eating.

5 Release the left fork/spoon.

6.Release the right fork/spoon.

7.Stop.

Program

/* Program to implement the solution to dinning philosophers' problem.

* This program uses five thread functions as five philosophers.

* The spoons or forks are represented with five semaphore variables.

* To use shared memory just include the code after the sem_wait() in each thread.

* To compile use 'cc diningphilosopher.c -lpthread'.

* To run './a.out'.



//inculsion#include<stdio.h>#include<pthread.h>#include<semaphore.h>

//macro definition#define cls() printf("\033[H\033[J")#define EATINGTIME 1

//function prototype for the thread function.void * philosopher1();void * philosopher2();void * philosopher3();void * philosopher4();void * philosopher5();

//global decalration of semaphore variables.sem_t sem15,sem12,sem23,sem34,sem45;

//global variable to control the execution of main.int end=0;

int main(){ char a[2];

pthread_t t1,t2,t3,t4,t5; pthread_attr_t at1;

pthread_attr_init(&at1); pthread_attr_setdetachstate(&at1,PTHREAD_CREATE_DETACHED);

sem_init(&sem15,0,1); sem_init(&sem12,0,1); sem_init(&sem23,0,1); sem_init(&sem34,0,1); sem_init(&sem45,0,1);

cls(); printf("\n\n\n\n\n\n"); printf("_____________________________________________________________________________________");

printf("\n\n\n\t\t\tDINNING PHILOSOPHER PROBLEM."); printf("\n\t\t\t____________________________");

printf("\n\n\t\tNO. OF PHILOSOPHERS :5");printf("\n\n\t\tNO. OF FORKS(SPOONS):5\n\n"); printf("_____________________________________________________________________________________");



printf("\n\n\n\t\tPRESS ENTER TO CONTINUE....................."); fgets(a,2,stdin);

cls(); pthread_create(&t1,&at1,philosopher1,NULL); pthread_create(&t2,&at1,philosopher2,NULL); pthread_create(&t3,&at1,philosopher3,NULL); pthread_create(&t4,&at1,philosopher4,NULL); pthread_create(&t5,&at1,philosopher5,NULL);

while(end!=5) { }}

//definition of philosopher1.void * philosopher1(){ int i=0;

printf("\n\t\tPHILOSOPHER-1 THINKING.\n");

while(i<EATINGTIME) { sleep(1);

//waiting to acquire the forks. sem_wait(&sem15); sem_wait(&sem12);

printf("\n\t\t\t* PHILOSOPHER-1 EATING.*\n");

sleep(1);//releasing the forks

sem_post(&sem15); sem_post(&sem12);


i++; } end++;}

//philosopher2.void * philosopher2(){



int i=0;



sem_wait(&sem12); sem_wait(&sem23);


sleep(1);



i++; } end++;}

//philosopher 3void * philosopher3(){ int i=0;





sleep(1);





i++; } end++;}

//philosopher 4.void * philosopher4(){ int i=0;





sleep(1);



i++; } end++;}

//philosopher 5.void * philosopher5(){ int i=0;






printf("\n\t\t\t* PHILOSOPHER-5 EATING.*\n"); sleep(1); sem_post(&sem45); sem_post(&sem15);

printf("\n\t\tPHILOSOPHER-5 THINKING.\n"); i++; } end++;}

Output



BANKER’S ALGORITHM



Theory

The Banker's algorithm is a resource allocation & deadlock avoidance algorithm

developed by Edsger Dijkstra that tests for safety by simulating the allocation of pre-

determined maximum possible amounts of all resources, and then makes a "safe-state" check

to test for possible deadlock conditions for all other pending activities, before deciding

whether allocation should be allowed to continue.

The algorithm was developed in the design process for the THE operating system and

originally described (in Dutch) in EWD108[1]. The name is by analogy with the way that

bankers account for liquidity constraints.

The Banker's algorithm is run by the operating system whenever a process requests

resources.The algorithm prevents deadlock by denying or postponing the request if it

determines that accepting the request could put the system in an unsafe state (one where

deadlock could occur).

Resources

For the Banker's algorithm to work, it needs to know three things:

How much of each resource each process could possibly request

How much of each resource each process is currently holding

How much of each resource the system has available

Some of the resources that are tracked in real systems are memory, semaphores and interface

access.

Example

Assuming that the system distinguishes between four types of resources, (A, B, C and D), the

following is an example of how those resources could be distributed. Note that this example

shows the system at an instant before a new request for resources arrives. Also, the types and


http://en.wikipedia.org/wiki/Interface_(computer_science)

http://en.wikipedia.org/wiki/Semaphore_(programming)

http://en.wikipedia.org/wiki/Memory_(computers)


http://en.wikipedia.org/wiki/Liquidity

http://en.wikipedia.org/wiki/Banker's_algorithm#_note-0%23_note-0

http://en.wikipedia.org/wiki/Dutch_language


http://en.wikipedia.org/wiki/THE_(operating_system)

http://en.wikipedia.org/wiki/Resource_(computer_science)

http://en.wikipedia.org/wiki/Edsger_Dijkstra

http://en.wikipedia.org/wiki/Algorithm

http://en.wikipedia.org/wiki/Deadlock

http://en.wikipedia.org/wiki/Resource_allocation


number of resources are abstracted. Real systems, for example, would deal with much larger

quantities of each resource.

Available system resources:

A B C D

3 1 1 2

Processes (currently allocated resources):

A B C D

P1 1 2 2 1

P2 1 0 3 3

P3 1 1 1 0

Processes (maximum resources):

A B C D

P1 3 3 2 2

P2 1 2 3 4

P3 1 1 5 0

Safe and Unsafe States

A state (as in the above example) is considered safe if it is possible for all processes to finish

executing (terminate). Since the system cannot know when a process will terminate, or how

many resources it will have requested by then, the system assumes that all processes will

eventually attempt to acquire their stated maximum resources and terminate soon afterward.

This is a reasonable assumption in most cases since the system is not particularly concerned

with how long each process runs (at least not from a deadlock avoidance perspective). Also,

if a process terminates without acquiring its maximum resources, it only makes it easier on

the system.

Given that assumption, the algorithm determines if a state is safe by trying to find a

hypothetical set of requests by the processes that would allow each to acquire its maximum

resources and then terminate (returning its resources to the system). Any state where no such

set exists is an unsafe state.



Example

We can show that the state given in the previous example is a safe state by showing that it is

possible for each process to acquire its maximum resources and then terminate.

1. P1 acquires 2 A, 1 B and 1 D more resources, achieving its maximum

o The system now still has 1 A, no B, 1 C and 1 D resource available

2. P1 terminates, returning 3 A, 3 B, 2 C and 2 D resources to the system

o The system now has 4 A, 3 B, 3 C and 3 D resources available

3. P2 acquires 2 B and 1 D extra resources, then terminates, returning all its resources

o The system now has 5 A, 3 B, 6 C and 6 D resources

4. P3 acquires 4 C resources and terminates

o The system now has all resources: 6 A, 4 B, 7 C and 6 D

5. Because all processes were able to terminate, this state is safe

Note that these requests and acquisitions are hypothetical. The algorithm generates them to

check the safety of the state, but no resources are actually given and no processes actually

terminate. Also note that the order in which these requests are generated – if several can be

fulfilled – doesn't matter, because all hypothetical requests let a process terminate, thereby

increasing the system's free resources.

For an example of an unsafe state, look at what would happen if process 2 were holding 1

more unit of resource B at the beginning.

Requests

When the system receives a request for resources, it runs the Banker's algorithm to determine

if it is safe to grant the request. The algorithm is fairly straight forward once the distinction

between safe and unsafe states is understood.

1. Can the request be granted?

o If not, the request is impossible and must either be denied or put on a waiting

list



2. Assume that the request is granted

3. Is the new state safe?

o If so grant the request

o If not, either deny the request or put it on a waiting list

Whether the system denies an impossible or unsafe request or makes it wait is an operating

system specific decision.

Continuing the previous examples, assume process 3 requests 2 units of resource C.

1. There is not enough of resource C available to grant the request

2. The request is denied

On the other hand, assume process 3 requests 1 unit of resource C.

1. There are enough resources to grant the request

2. Assume the request is granted

o The new state of the system would be:

Available system resources: A B C D

Free 3 1 0 2


A B C D

P1 1 2 2 1

P2 1 0 3 3

P3 1 1 2 0


A B C D

P1 3 3 2 2



P2 1 2 3 4

P3 1 1 5 0

1. Determine if this new state is safe

1. P1 can acquire 2 A, 1 B and 1 D resources and terminate

2. Then, P2 can acquire 2 B and 1 D resources and terminate

3. Finally, P3 can acquire 3 C resources and terminate

4. Therefore, this new state is safe

2. Since the new state is safe, grant the request

Finally, assume that process 2 requests 1 unit of resource B.

1. There are enough resources

2. Assuming the request is granted, the new state would be:

Available system resources:

A B C D

Free 3 0 1 2


A B C D

P1 1 2 2 1

P2 1 1 3 3

P3 1 1 1 0


A B C D

P1 3 3 2 2

P2 1 2 3 4

P3 1 1 5 0

1. Is this state safe? Assuming P1, P2, and P3 request more of resource B and C.

o P1 is unable to acquire enough B resources

o P2 is unable to acquire enough B resources

o P3 is unable to acquire enough C resources



o No process can acquire enough resources to terminate, so this state is not safe

2. Since the state is unsafe, deny the request

Algorithm

* The algorithm for the process is...........

1. Start.

2. Wait for the request.

3. If the request is for allocation then

i. Obtain the request.

ii. Check for safe state.

iii. If safe state detected then allocate resources.

Else put the request in the waiting stack.

Else (for deallocation)

i.Deallocate the resources.

ii. Process the request of the process in the

wait stack.

4. Stop.

Program

/* Program to demonstrate the working of the BANKERS ALGORITHM.

* This program gives a general idea of how the operating system process allocates

resources to the requesting processes.

* Here it is assumed that request are collected in a 'req_queue' whose type is stored in

'req_type'.

* It has been assumed that there are 3 processes which can request for 4 different types

of resources say A,B,C & D.



* The program works with certain assumed values as shown below.........

AVAILABLE RESOURCE MATRIX.

| A | B | C | D| |___|____|____|___|_ | 3 | 1 | 1 | 2|

CURRENTLY ALLOCATED RESOURCES.

| A | B | C | D | ___|___|____|____|____| P1| 1 | 2 | 2 | 2 | ___|___|____|____|____| P2| 1 | 0 | 3 | 3 | ___|___|____|____|____| P3| 1 | 1 | 1 | 0 | ___|___|____|____|____|

MAXIMUM REQUIRED RESOURCES.

| A | B | C | D | ___|___|___|___|___| P1| 3 | 3 | 2 | 2 | ___|___|___|___|___| P2| 1 | 2 | 3 | 4 | ___|___|___|___|___| P3| 1 | 1 | 1 | 0 | ___|___|___|___|___|

* This module can be compiled using 'cc bankersalgorithm.c' and executed using './a.out'

//inculsion.#include<stdio.h>

//macro definition#define cls() printf("\033[H\033[J")#define delay() for(h=0;h<30000;h++){for(k=0;k<30000;k++){}}

//function prototype.void getrequest(int);int issafe();void allocate(int);void deallocate(int);void display();

//global matrixes as shown above.int available_res[4],cur_allocated_res[3][4],max_req_res[3][4],request[4];



int main(){ int req_queue[10],wait_queue[10],req_type[10],i,j,h,k;

//inserting the assumed values. available_res[0]=3; available_res[1]=1; available_res[2]=1; available_res[3]=2;

cur_allocated_res[0][0]=1;cur_allocated_res[0][1]=2;cur_allocated_res[0][2]=2;cur_allocated_res[0][3]=1;



max_req_res[0][0]=3; max_req_res[0][1]=3; max_req_res[0][2]=2; max_req_res[0][3]=2;

max_req_res[1][0]=1; max_req_res[1][1]=2; max_req_res[1][2]=3; max_req_res[1][3]=4;

max_req_res[2][0]=1; max_req_res[2][1]=1; max_req_res[2][2]=1; max_req_res[2][3]=0;//assuming the request.

req_queue[0]=0;req_queue[1]=1;req_queue[2]=2;req_queue[3]=0;req_queue[4]=2;req_queue[5]=1;

req_type[0]=0;req_type[1]=0;req_type[2]=0;req_type[3]=1;req_type[4]=1;req_type[5]=1;

display(); i=0;j=0;

while(i<6) { cls(); printf("\n\t\t\tWaiting for the request.............\n");

delay(); printf("\n\tRequest obtained from the process P%d ",req_queue[i]+1); if(req_type[i]==0) { printf("for resource allocation.\n"); printf("\nGetting request.....\n");

getrequest(req_queue[i]);



printf("\nChecking safe state.....\n"); delay(); if(issafe()) { printf("\nSafe state detected....\nAllocating resources .......\n"); allocate(req_queue[i]); } else { printf("\nUnsafe state detected....\nInserting the process into waiting queue.\n"); j=j+1; wait_queue[j]=req_queue[i]; } }

else { printf("for resource deallocation.\n"); deallocate(req_queue[i]); printf("\nDeallocation done.\n\n%d processes in the wait queue\n",j); if(j>0) { while(j>0) { printf("\nConsidering the waiting queue process P%d\n",wait_queue[j]+1); getrequest(wait_queue[j]); printf("\nChecking safe state.\n"); delay(); if(issafe()) { printf("\nSafe state detected\nResources allocated\n"); allocate(wait_queue[j]); j--; } else { break; } } } } delay(); i++; }}



void getrequest(int i){ int j; for(j=0;j<4;j++) { request[j]=max_req_res[i][j]-cur_allocated_res[i][j]; }}

int issafe(){ int j; for(j=0;j<4;j++) { if(request[j]>available_res[j]) { return 0; } } return 1;}

void allocate(int i){ int j;

for(j=0;j<4;j++) { cur_allocated_res[i][j]=cur_allocated_res[i][j]+request[j]; available_res[j]=available_res[j]-request[j]; }}

void deallocate(int i){ int j;

for(j=0;j<4;j++) { available_res[j]=available_res[j]+cur_allocated_res[i][j]; cur_allocated_res[i][j]=0; }}

void display(){ int i,j;



char a[3];

cls(); printf("\n\n\n\n\n\n\n\n"); printf("_____________________________________________________________________________________"); printf("\n\n\n\n\t\t\t\tBANKERS ALGORITHM.\n"); printf("\t\t\t\t__________________\n\n\n"); printf("\n\n\n\n\t\tPRESS ENTER TO CONTINUE.................."); fgets(a,2,stdin); cls();

printf("\n\n\t\t\t\tDETAILS."); printf("\n\t\t\t\t________");

printf("\n\n\t\tNO OF PROCESSES:\tP1 P2 P3"); printf("\n\n\t\tNO OF RESOURCES:\tA B C D");

printf("\n\n\t\t\tThe status .............");

printf("\nThe available resources are.\n\t\tA B C D\n\t\t");

for(i=0;i<4;i++) { printf("%d ",available_res[i]); } printf("\nThe currently allocated resources are...\n\t\t A B C D\n\t\t");

for(i=0;i<3;i++) { printf("P%d ",i+1); for(j=0;j<4;j++) { printf("%d ",cur_allocated_res[i][j]); } printf("\n\t\t"); }

printf("\nThe maximum required resources are...\n\t\t A B C D\n\t\t");

for(i=0;i<3;i++) { printf("P%d ",i+1); for(j=0;j<4;j++) { printf("%d ",max_req_res[i][j]);



} printf("\n\t\t"); }

printf("\n\n\tPRESS ENTER TO START THE PROCESS...\n"); fgets(a,2,stdin);}

Output









FLOPPY SIZE

Program

/* Program to find the disk space details of the floppy disk.

* This program uses the function call 'statvfs()' to find the details.

* This program gives details about the 'TOTAL', 'FREE' and 'USED' spaces of the disk.

* To run this program initially a file named 'temp.c' should be copied on to the floppy disk.

* Then compile as usual (cc floppydisksize.c)and run the program(./a.out).

NOTE: In linux the path name for floppy drive is :/media/floppy/.......(After mounting)

*/

//inculsion#include<stdio.h>#include<sys/statvfs.h>

int main(){

//variables to store the disk spaces. unsigned long totalblocks,blocksize,freeblocks;

char * filename="/media/floppy/temp.c"; struct statvfs buf;

if(!statvfs(filename,&buf)) {

//retriving the total no. of blocks. totalblocks=buf.f_blocks;

//retriving the blocksize. blocksize=buf.f_bsize;

//retriving the free disk space.



freeblocks=buf.f_bfree;

printf("\n\tThe total disk size:\t%lu (bytes)\n",totalblocks*blocksize); printf("\n\tThe free disk space:\t%lu (bytes)\n",freeblocks*blocksize); printf("\n\tThe used disk space:\t%lu (bytes)\n",(totalblocks*blocksize)-(freeblocks*blocksize)); } else { printf("\nERROR:Cannot open the file specified.\n"); }}

Output

64 ./nw

336 .

FileSystem Size Used Avail Use % Mounted On

/dev/mapper/VolGroup00-Log Vo100

35G 3.2G 30G 10% /

/dev/hda1 99M 12M 82M 13% /boot

None 498M 0 498M 0% /dev/shm



PIPES

Theory

A pipe is a method of connecting the standard output of one process to the standard

input of another. Pipes are the eldest of the IPC tools, having been around since the earliest

incarnations of the UNIX operating system. They provide a method of one-way

communications (hence the term half-duplex) between processes.

This feature is widely used, even on the UNIX command line (in the shell).

When a process creates a pipe, the kernel sets up two file descriptors for use by the

pipe. One descriptor is used to allow a path of input into the pipe (write), while the other is

used to obtain data from the pipe (read). At this point, the pipe is of little practical use, as the

creating process can only use the pipe to communicate with itself.

While a pipe initially connects a process to itself, data traveling through the pipe

moves through the kernel. Under Linux, in particular, pipes are actually represented

internally with a valid inode. Of course, this inode resides within the kernel itself, and not

within the bounds of any physical file system. This particular point will open up some pretty

handy I/O doors for us, as we will see a bit later on.

At this point, the creating process typically forks a child process. Since a child

process will inherit any open file descriptors from the parent, we now have the basis for

multiprocess communication (between parent and child). It is at this stage, that a critical

decision must be made. In which direction do we desire data to travel? Does the child process

send information to the parent, or vice-versa? The two processes mutually agree on this issue,

and proceed to ``close'' the end of the pipe that they are not concerned with.

To access a pipe directly, the same system calls that are used for low-level file I/O

can be used (recall that pipes are actually represented internally as a valid inode).



To send data to the pipe, we use the write() system call, and to retrieve data from the

pipe, we use the read() system call. Remember, low-level file I/O system calls work with file

descriptors! However, keep in mind that certain system calls, such as lseek(), do not work

with descriptors to pipes.

To create a simple pipe with C, we make use of the pipe() system call. It takes a

single argument, which is an array of two integers, and if successful, the array will contain

two new file descriptors to be used for the pipeline.

SYSTEM CALL: pipe();

PROTOTYPE: int pipe( int fd[2] );

RETURNS: 0 on success

-1 on error: errno = EMFILE (no free descriptors)

EMFILE (system file table is full)

EFAULT (fd array is not valid)

NOTES: fd[0] is set up for reading, fd[1] is set up for writing

The popen() function creates a pipe between the calling program and the

command to be executed. The arguments topopen() are pointers to null-terminated strings.

The com-mand argument consists of a shell command line. The modeargument is an I/O

mode, either r for reading or w for writing. The value returned is a stream pointer such that

one can write to the standard input of the command, if the I/Omode is w, by writing to the

file stream and one can read from the standard output of the command, if the I/O mode is r,

by reading from the file stream.

The pclose() function closes a stream opened by popen() by closing the pipe. It

waits for the associated process to terminate and returns the termination status of the process

running the command language interpreter. This is the value returned by waitpid(2).


http://bama.ua.edu/cgi-bin/man-cgi?waitpid+2


SIMPLE PIPES OR LOWLEVEL PIPES

Program

/* Program to demonstrate the creation and use of simple/low level pipe.

* This program creates a pipe that connects the child process with its parent process.

* Here the child process writes 'REQUEST FROM CHILD PROCESS.' on to the pipe

which is read by the parent process.

* The function 'fork()' is a system call used to create a child process.

* This module can be compiled using 'cc simplepipe.c' and executed using './a.out'

//inculsion#include<stdio.h>#include<sys/types.h>

int main(){

//array to store the pipe pointers returned by the pipe() function. int pipe_pointer[2];

//variable to store the child process id. pid_t child; char message[50];

//creating a pipe pipe(pipe_pointer);

//creating a child process. child=fork();

if(child==0) { printf("\nThe child process is writing.\n");

//closing the read pointer. close(pipe_pointer[0]);

//writing on to the pipe. write(pipe_pointer[1],"REQUEST FROM CHILD PROCESS.",sizeof("REQUEST FROM CHILD PROCESS.")); } else {



printf("\nThe parent process is reading.\n");

//closing the write pointer. close(pipe_pointer[1]);

//reading from the pipe. read(pipe_pointer[0],message,sizeof(message));

printf("\nThe parent has read:\n\n** %s **\n",message); }

close(pipe_pointer[0]); close(pipe_pointer[1]);}

Output



FORMATTED PIPE

/* Program to demonstrate the creation and use of formatted pipe.

* This program creates a formatted pipe which is connected to the system process

denoted by the command 'CMD'.

* The pipe is established for reading and the read content is displayed.

* This module can be compiled using 'cc formattedpipe.c' and executed './a.out'.*/

//inculsion part#include<stdio.h>#include<string.h>

#define CMD "cal"

int main(){ FILE *ptr; char message[100]; char cmd[20];

strcpy(cmd,CMD);//creating a formatted pipe.

ptr=popen(cmd,"r"); while( fgets(message,sizeof(message),ptr)!=NULL) { printf("%s",message); }

//closing the pipe. pclose(ptr);}



Output



SHARED MEMORY

Theory

In computing, shared memory is a memory that may be simultaneously accessed by

multiple programs with an intent to provide communication among them. Depending on

context, programs may run on the same physical processor or on separate ones. Using

memory for communication inside a single program, for example among its multiple threads,

is generally not referred to as shared memory.

In computer software, shared memory is a method of inter-process communication

(IPC), i.e. a way of exchanging data between programs running at the same time. One

process will create an area in RAM which other processes can access.

Since both processes can access the shared memory area like regular working

memory, this is a very fast way of communication (as opposed to other mechanisms of IPC

such as named pipes, Unix sockets or CORBA). On the other hand, it is less powerful, as for

example the communicating processes must be running on the same machine (whereas other

IPC methods can use a computer network).

IPC by shared memory is mainly used on Unix systems.

POSIX provides a standardized API for using shared memory, POSIX Shared

Memory. This uses the function shm_open from sys/mman.h.

Shared Memory is an efficeint means of passing data between programs. One

program will create a memory portion which other processes (if permitted) can access.


http://en.wikipedia.org/wiki/POSIX


http://en.wikipedia.org/wiki/Computer_network

http://en.wikipedia.org/wiki/CORBA

http://en.wikipedia.org/wiki/Unix_socket

http://en.wikipedia.org/wiki/Named_pipe

http://en.wikipedia.org/wiki/RAM


http://en.wikipedia.org/wiki/Inter-process_communication

http://en.wikipedia.org/wiki/Thread

http://en.wikipedia.org/wiki/Computing


In the Solaris 2.x operating system, the most efficient way to implement shared

memory applications is to rely on the mmap() function and on the system's native virtual

memory facility. Solaris 2.x also supports System V shared memory, which is another way to

let multiple processes attach a segment of physical memory to their virtual address spaces.

When write access is allowed for more than one process, an outside protocol or mechanism

such as a semaphore can be used to prevent inconsistencies and collisions.

A process creates a shared memory segment using shmget()|. The original owner of a

shared memory segment can assign ownership to another user with shmctl(). It can also

revoke this assignment. Other processes with proper permission can perform various control

functions on the shared memory segment using shmctl(). Once created, a shared segment can

be attached to a process address space using shmat(). It can be detached using shmdt() (see

shmop()). The attaching process must have the appropriate permissions for shmat(). Once

attached, the process can read or write to the segment, as allowed by the permission

requested in the attach operation. A shared segment can be attached multiple times by the

same process. A shared memory segment is described by a control structure with a unique ID

that points to an area of physical memory. The identifier of the segment is called the shmid.

The structure definition for the shared memory segment control structures and prototypews

can be found in <sys/shm.h>.

Accessing a Shared Memory Segment

shmget() is used to obtain access to a shared memory segment. It is prottyped by:

int shmget(key_t key, size_t size, int shmflg);

The key argument is a access value associated with the semaphore ID. The size

argument is the size in bytes of the requested shared memory. The shmflg argument specifies

the initial access permissions and creation control flags.

When the call succeeds, it returns the shared memory segment ID. This call is also

used to get the ID of an existing shared segment (from a process requesting sharing of some

existing memory portion).



The following code illustrates shmget():

#include <sys/types.h>#include <sys/ipc.h> #include <sys/shm.h>

... key_t key; /* key to be passed to shmget() */ int shmflg; /* shmflg to be passed to shmget() */ int shmid; /* return value from shmget() */ int size; /* size to be passed to shmget() */

... key = ... size = ...shmflg) = ...

if ((shmid = shmget (key, size, shmflg)) == -1) { perror("shmget: shmget failed"); exit(1); } else { (void) fprintf(stderr, "shmget: shmget returned %d\n", shmid); exit(0); }...

Controlling a Shared Memory Segment

shmctl() is used to alter the permissions and other characteristics of a shared memory segment. It is prototyped as follows:

int shmctl(int shmid, int cmd, struct shmid_ds *buf);

The process must have an effective shmid of owner, creator or superuser to perform this command. The cmd argument is one of following control commands:

SHM_LOCK -- Lock the specified shared memory segment in memory. The process must have the effective ID of superuser to perform this command.

SHM_UNLOCK -- Unlock the shared memory segment. The process must have the effective ID of superuser to perform this command.

IPC_STAT -- Return the status information contained in the control structure and place it in the buffer pointed to by buf. The process must have read permission on the segment to perform this command.

IPC_SET



-- Set the effective user and group identification and access permissions. The process must have an effective ID of owner, creator or superuser to perform this command.

IPC_RMID -- Remove the shared memory segment.

The buf is a sructure of type struct shmid_ds which is defined in <sys/shm.h>

Program

Server

/*Program to demonstrate the use of shared memory in interprocess communication.

* This program acts as a server which waits for a message from the client process.

* The process is implemented using a shared memory space called 'shared_location'.

* The 'message' part of this space stores the message while the 'written' part is used to

indicate whether the server has read the message or the client has written the

message.(0->read,1->written).

* This module should be compiled and executed first.

* This module is compile using 'cc shmserver.c' and executed using './a.out'*/

//inculsion#include<stdio.h>#include<unistd.h>#include<string.h>

#include<sys/types.h>#include<sys/ipc.h>#include<sys/shm.h>

//structure definition for acquiring a shared location.struct shared_location{ int written; char message[30];};

int main(){ int shmid,running;



void *address; struct shared_location * ptr;

//for getting a shared location shmid=shmget((key_t)1234,sizeof(struct shared_location),0666|IPC_CREAT);

//optional if required for error checking. if(shmid<=0) { printf("\nERROR:\tCannot allocate shared space.\n"); exit(0); }

//attaching the shared location to this process. address=shmat(shmid,(void *)0,0);

//optional if required for error checking. if(address==(void*)0) { printf("\nEROOR:\tShared location cannot be attached.\n"); }

//type casting so as to convert the obyained location into our format. ptr=(struct shared_location*)address;

ptr->written=0; strcpy(ptr->message,"Hi I am server."); running=1;

while(running) { printf("\nWaiting for the client to enter the message.\n"); while(ptr->written==0) { } if(ptr->written==1) { printf("The client has entered the message: %s\n",ptr->message); } ptr->written=0; if(strcmp(ptr->message,"end")==0) { running=0; } }

//detaching the shared location. shmdt(address);



//deleting the shared location. shmctl(shmid,IPC_RMID,NULL);}

Output

Client

Program

/* Program to demonstrate the use of shared memory in interprocess communication.

* This module acts as a client which sends messages to the server process.

* In this the message entered into the message part of the 'shared_location' structure and

the 'written' field is set to 1.

* The remaining process is similar to that of the server process.

* This module can be compiled using 'cc shmclient.c -o b' and executed using './b'

//inculsion



#include<stdio.h>#include<unistd.h>#include<string.h>

#include<sys/types.h>#include<sys/ipc.h>#include<sys/shm.h>

//structure definition for the shared location.struct shared_location{ int written; char message[30];};//the functions and other terms used have similar meanings to that used in the server module //but they don't bear any specific relationship.

int main(){ int shmid,running; void *address; struct shared_location * ptr;

shmid=shmget((key_t)1234,sizeof(struct shared_location),0666|IPC_CREAT); if(shmid<=0) { printf("\nERROR:\tCannot allocate shared memory.\n"); exit(0); }

address=shmat(shmid,(void*)0,0); if(address==(void*)0) { printf("\nERROR:\tCannot attach the shared location\n"); exit(0); }

ptr=(struct shared_location*)address; running=1;

while(running) { printf("\nWaiting for the server\n"); while(ptr->written==1) { } printf("\nEnter your message.(type 'end' to exit)\n");



scanf("%s",ptr->message); ptr->written=1; if(strcmp(ptr->message,"end")==0) { running=0; } } address=shmat(shmid,(void *)0,0); shmdt(address);}

Output



SOME SAMPLE PROGRAMS

1.Program for executing LINUX commands through C program using system command

#include<stdio.h>main(){printf("\nDirectory Listing\n");system("ls -l");printf("Directory Listing Completed");}

Using exec command

#include<stdio.h>main(){printf("\nThe Directory Listing\n");execl("/bin/ls","ls","-l",NULL);printf("This Line will not be printed");}

2.Program to fork a child process and display details of parent & child processes

#include<sys/types.h>main(){int pid;pid=fork();if(pid==0){printf("I am child,My id is %d\n & my parents id is %d\n\n",getpid(),getppid());}else{printf("I am parent,My id is %d\n\n",getpid());printf("My child is %d\n\nMy Parent is %d",pid,getppid());}}



3.Program to call a new process using EXEC function from a child process

#include<sys/types.h>main(){int pid;printf("Program begins\n\n");pid=fork();

if(pid==0){

printf("I am child,My id is %d\n & my parents id is %d\n\n",getpid(),getppid());execl("f2",0);printf("Child Terminated");}else{printf("I am parent,My id is %d\n\n",getpid());printf("My child is %d\n\nMy Parent is %d",pid,getppid());}}

// Create another simple program. Compile it to f2( redirect output to f2). f2 will be executed by the above written program.

3. Program to demonstrate interprocess communication between a parent process and a child process.

//This is to and fro communication through a single pipe.

#include<stdio.h>#include<sys/types.h>

main(){int pid,fd[2];char buf[50];pipe(fd);pid=fork();if(pid==0){

printf("%d %d",pid,getppid());



printf("Enter the data for the parent");fgets(buf,sizeof(buf),stdin);write(fd[1],buf,sizeof(buf));sleep(20);read(fd[0],buf,sizeof(buf));printf("Got From Parent");puts(buf);

}else{

sleep(10);printf("In Child %d %d ",pid,getppid());read(fd[0],buf,sizeof(buf));printf("From Child");puts(buf);printf("I am Parent");printf("Enter message for Child");fgets(buf,sizeof(buf),stdin);write(fd[1],buf,sizeof(buf));

}}

5.Suppose we are given a number N which is quite large. We need to find all its factors. We decide to have some computation in parallel so we divide the N by the range of numbers from 2 to √N/2 and √N/2 +1. We fork two child processes to work over each of these ranges. Write a program to implement the above scheme using fork(). The parent should output only distinct factors.

#include<stdio.h>#include<sys/types.h>#include<unistd.h>

void firstfact(int n);void secondfact(int n);int i,j=0;main(){int fd1[2],fd2[2],n,j=0,i,pid1,pid2;int factor[20];pipe(fd1);pipe(fd2);pid1=fork();if(pid1){

pid2=fork(); //child1



if(pid2==0){

read(fd1[0],&n,sizeof(n));firstfact(n);

}//parentelse{scanf("%d",&n);write(fd1[1],&n,sizeof(n));write(fd2[1],&n,sizeof(n));}

}

//child2else{

read(fd2[0],&n,sizeof(n)); secondfact(n);

}}

void firstfact(int n){

for(i=2;i<(sqrt(n)/2);i++){if(n%i==0)

{//printf("child");

printf("\n%d >>>>child1",i); }

}

}void secondfact(int n){

for(i=((sqrt(n/2)+1);i<=(n/2);i++){

if(n%i==0){



//printf("parent");printf("\n%d >>>child2",i);}

}

}

6. Write a program to detect deadlock when a number of processes are running. The number of available resources, number of resources allocated to processes are accepted..

#include<stdio.h>

void read_alloc(int A[10][10],int m , int n ){

int i ,j ;for(i=0;i<n;i++){printf("for process %d the no: of allocated resources of .....\n",i);for(j=0;j<m;j++){printf("type%d:",j);

scanf ("%d",&A[i][j]);}}

}void read_reqst(int RQ[10][10],int m,int n){

int i ,j ;for (i=0;i<n;i++){printf("for process %d the no: of required resources of .....\n",i);

for(j=0;j<m;j++){printf("type%d:",j);

scanf ("%d",&RQ[i][j]);}}

}void read_avail(int A[10],int m ){ int i ;

printf("Enter the available resources of ........\n");



for (i=0;i<m ;i++){printf("Type %d ",i);scanf("%d",&A[i]);}

}void calc_deadlock(int A[10][10],int RQ[10][10],int AVAIL[10],int m,int n ){

int w[10],f[10],i,j,fg=0;for(i=0;i<m;i++)w[i]=AVAIL[i];for(i=0;i<n;i++){

fg=0;for(j=0;j<m;j++){if (A[i][j]!=0){fg=1;

break;}}

if (fg==0)f[i]=1;else

f[i]=0;}for(i=0;i<n;i++){

fg=0;for(j=0;j<n;j++){if (RQ[i][j]>w[j]){

fg=1; break;

}}if(fg==0 && f[i]==0){for(j=0;j<m;j++)w[j]=w[j]+A[i][j];f[i]=1;i=0;}

}



fg=0;for(i=0;i<n;i++){

if (f[i]==0){

printf(" the system is in deadlock by the process %d ....",i);getchar();fg=1;break;}}

if (fg==0){printf(" there is no deadlock");getchar();}

}

int main(){int m , n , A[10][10],AVAIL[10],RQ[10][10];system("clear");printf("enter the total number of processes running:");scanf("%d",&n);printf (" enter the total no: of resource types :");scanf ("%d",&m);read_alloc(A,m,n);system("clear");read_reqst(RQ,m,n);system("clear");read_avail(AVAIL,m);calc_deadlock(A,RQ,AVAIL,m,n);getchar();}

7.Write a program to send and receive messages through message queue

Sending Program

//Message Queue....Sending Data...

#include<stdio.h>#include<string.h>#include<stdlib.h>#include<unistd.h>#include<sys/types.h>



#include<sys/ipc.h>#include<sys/msg.h>typedef struct msgbuf{

long mtype;char data[30];

}message;int main(){

message send,rec;key_t key=3151; //else use FTOK function to generate a unique key value

int msgid=msgget(key,IPC_CREAT|0666);if(msgid==-1){

fprintf(stderr,"Error Creating Or Opening mq\n");return EXIT_FAILURE;

}do{

fprintf(stdout,"Enter Some Valid Data To Send");fgets(send.data,30,stdin);send.mtype=1;if(msgsnd(msgid,(void *)& send,30,1)==-1){

fprintf(stderr,"Error Writting To mq\n");return EXIT_FAILURE;

}}while(strncmp(send.data,"quit",4)!=0);

return EXIT_SUCCESS;}

Receiving Program

//Message Queue....Receiving Data...

#include<stdio.h>#include<string.h>#include<stdlib.h>#include<unistd.h>#include<sys/types.h>#include<sys/ipc.h>#include<sys/msg.h>typedef struct msgbuf{



long mtype;char data[30];

}message;

int main(){

message send,rec;student s;int i;key_t key=3151;sleep(20);printf("In Process 2");

int msgid=msgget(key,IPC_CREAT|0666);if(msgid==-1){

fprintf(stderr,"Error Creating Or Opening mq\n");return EXIT_FAILURE;

}sleep(20);int j=0;do{

j++;if(msgrcv(msgid,(void *)&rec,30,1,0)==-1){

fprintf(stderr,"Error Writting To mq\n");break;

}fprintf(stdout,"Receiver Got %s\n",rec.data);

}while(strncmp(send.data,"quit",4)!=0);

}

8.Suppose we have 4 matrices A , B, C and D , each of size N X N , we need to compute the matrix product A X B, A X C , A X D . Write a pgm to compute the desired result using shared memory mechanism.

//MATRIX MULTIPLICATION(SHM1.C)#include<stdio.h>#include<sys/shm.h>#include<sys/stat.h>



#include<string.h>#include<sys/types.h>#include<unistd.h>#define size 4096

//CONVERTING STARTING ADDRESS OF SHARED MEMORY TO STRINGvoid itoa(char *str,int n){ int i=100000,j=0; for(j=0;j<6;++j)

{ str[j]=n/i+48; n=n%i; i=i/10;}str[j]='\0';

}

//READ MATRIX FROM KEYBOARD AND STORE TO SHARED MEMORYvoid read_matrix(int address,int A[10][10],int r,int c,int *shared_mem){

int i,j;for(i=0;i<r;++i){

printf("\n");for(j=0;j<c;++j){ scanf("%d",&A[i][j]); shared_mem[address]=A[i][j]; address++;}

}}

// MATRIX MULTIPLICATION

void multiply(int A[10][10],int B[10][10],int r1,int c1,int r2,int c2){

int i,j,k,C[10][10];for(i=0;i<r1;++i){

for(j=0;j<c1;++j){



C[i][j]=0;for(k=0;k<r2;++k)C[i][j]+=A[i][k]*B[k][j];

}}

printf("The result of A X B from process 1 is ..............\n");for(i=0;i<r1;++i){

printf("\n");for(j=0;j<c2;++j) printf("%8d",C[i][j]);

}}

int main(){

int sh_mem_id, *shared_mem;int r1,r2,c1,c2,r3,c3;int address=8,A[10][10],B[10][10],C[10][10];char str[10];pid_t child;

//INITIALIZE SHARED MEMORYsh_mem_id=shmget(IPC_PRIVATE,size,IPC_CREAT|IPC_EXCL|S_IRUSR|

S_IWUSR|S_IROTH|S_IWOTH);shared_mem=(int *)shmat(sh_mem_id,0,0);//ATTACH MEMORY

//CONVERT ADDRESS TO STRINGitoa(str,sh_mem_id);

system("clear");printf("Enter the rows and columns of matrix A.....\n");scanf("%d %d",&r1,&c1);

//STORE ROW AND COLUMN TO SHARED MEMORYshared_mem[0]=r1;shared_mem[1]=c1;

printf("\nEnter the elements of the matrix A....\n");read_matrix(address,A,r1,c1,shared_mem);

//INCREMENT SHARED MEMORY ADDRESSaddress=address+(r1*c1);

//FOR MATRIX B



system("clear");printf("enter the rows and columnsof matrix B....\n");scanf("%d %d",&r2,&c2);shared_mem[2]=r2;shared_mem[3]=c2;printf("enter the elementsof matrix B....\n");read_matrix(address,B,r2,c2,shared_mem);address=address+(r2*c2);

//FOR MATRIX Csystem("clear");printf("enter the rows and columnsof matrix C....\n");scanf("%d %d",&r3,&c3);shared_mem[4]=r3;shared_mem[5]=c3;printf("enter the elementsof matrix C....\n");read_matrix(address,C,r3,c3,shared_mem);address=address+(r3*c3);

//FOR MATRIX D system("clear");printf("enter the rows and columnsof matrix D.....\n");scanf("%d %d",&r3,&c3);shared_mem[6]=r3;shared_mem[7]=c3;printf("enter the elementsof matrix D...\n");read_matrix(address,C,r3,c3,shared_mem);address=address+(r3*c3);

//FORK A CHILDchild=fork();if(child ==0){

sleep(10);//INVOKE ANOTHER PROGRAM SHM2(EXE),PASS ARGUMENT- STR

execlp("./shm2","shm2",str,NULL);}multiply(A,B,r1,c1,r2,c2);shmdt(shared_mem);//DETACH SHARED MEMORYprintf("closing process 1...............\n");

}

//Process1 reads matrices from keyboard and stores to shared memory. AXB is simple computation without using shared memory. Write another program (shm2.c) The Shared



memory id is passed to this program through exec function. Exec takes only string arguments. So id value is converted to string.Shm2.c is compiled to shm2 and is called from process1.You have to run only process1. Locations 0 to 7 of shared memory contain number of rows and columns of 4 matrices. Actual matrix elements are stored from location 8 onwards.………………………………………………………………………………………………………………………………………………………………………………………….

shm2.c

//SHM2.C//COMPILE THIS TO SHM2

#include<stdio.h>#include<sys/shm.h>#include<sys/stat.h>#include<string.h>#include<sys/types.h>#include<unistd.h>#include<stdlib.h>

//READ THE MATRIX FROM SHARED MEMORYvoid read_from_shm(int A[10][10],int *shared_mem,int add,int r,int c){

int i,j;for(i=0;i<r;++i){

for(j=0;j<c;++j){ A[i][j]=shared_mem[add]; add++;}

}}

void multiply(int A[10][10],int B[10][10],int r1,int c1,int r2,int c2){

int i,j,k,C[10][10];for(i=0;i<r1;++i){

for(j=0;j<c1;++j){

C[i][j]=0;for(k=0;k<r2;++k)



C[i][j]+=A[i][k]*B[k][j];}

}

for(i=0;i<r1;++i){

printf("\n");for(j=0;j<c2;++j) printf("%8d",C[i][j]);

}}

int main(int argc,char *argv[]){

int *shared_mem,sh_mem_id;int r1,c1,r2,c2,r3,c3,add=8;int A[10][10],C[10][10],D[10][10];pid_t child;

//GET STARTING ADDRESS OF SHARED MEMORY FROM COMMAND LINE ARGUMENT

sh_mem_id=atoi(argv[1]);shared_mem=(int *)shmat(sh_mem_id,0,0);//ATTACH MEMORY

system("clear");//GET ROW& COLUMN FROM SHARED MEMORYr1=shared_mem[0];c1=shared_mem[1];//READ MATRIX Aread_from_shm(A,shared_mem,add,r1,c1);add=add+(r1*c1);

//SKIP MATRIX Br2=shared_mem[2];c2=shared_mem[3];add=add+(r2*c2);

//READ MATRIX Cr3=shared_mem[4];c3=shared_mem[5];read_from_shm(C,shared_mem,add,r3,c3);add=add+(r3*c3);printf("\n The Result of A X C from process 2.......\n");

multiply(A,C,r1,c1,r3,c3);



//READ MATRIX Dr3=shared_mem[6];c3=shared_mem[7];read_from_shm(D,shared_mem,add,r3,c3);sleep(3);printf("\n.. The Result of A X D from process 2..............\n");multiply(A,D,r1,c1,r3,c3);

printf("closing process 2.......\n");

//DETACH MEMORY shmdt(shared_mem);

//REMOVE MEMORYshmctl(sh_mem_id,IPC_RMID,0);

}

9. Implement Producer Consumer Problem

//CONSUMER PROGRAM

#include <stdio.h>#include <string.h>#include <unistd.h>#include <fcntl.h>

#define BUF_SIZE 30

int main(){ char write_fifo[] = "readFIFO"; char read_fifo[] = "writeFIFO";

//Check if the FIFO exists. If not, try to create it. if( access(write_fifo, F_OK)==-1 )

{ int result = mkfifo(write_fifo, 0777); if( result!=0 )

{ fprintf(stderr, "FIFO creation failed."); return 1;



} } if( access(read_fifo, F_OK)==-1 ){ int result = mkfifo(read_fifo, 0777); if( result!=0 ) { fprintf(stderr, "FIFO creation failed."); return 1; } } int r_pipe = open(read_fifo, O_RDONLY); int w_pipe = open(write_fifo, O_WRONLY);

if( w_pipe==-1 ) { fprintf(stderr, "Error opening %s\n", write_fifo); return 2; } if( r_pipe==-1 ) { fprintf(stderr, "Error opening %s\n", read_fifo); return 2; }

int bytes=0, i; char w_buffer[BUF_SIZE], r_buffer[BUF_SIZE]; do { //Read the string from the pipe. memset(r_buffer, '\0', sizeof(r_buffer)); read(r_pipe, r_buffer, sizeof(r_buffer)); fprintf(stdout, "I got %s\n", r_buffer); //Process the string; strcpy(w_buffer, r_buffer); for(i=0;i<strlen(w_buffer);++i) w_buffer[i] = w_buffer[i]+1;

//Write the string back into the pipe. bytes = write(w_pipe, w_buffer, strlen(w_buffer)); if( bytes==-1 ) fprintf(stderr, "Write error in FIFO!\n"); }while( strncmp(r_buffer, "quit", 4)!=0 );

close(w_pipe);



close(r_pipe);

fprintf(stdout, "WORKING Process finished [PID=%d]\n", (int)getpid() );

return 0;}

//PRODUCER PROGRAM

#include <stdio.h>#include <string.h>#include <unistd.h>#include <fcntl.h>

#define BUF_SIZE 30

int main(){ char write_fifo[] = "writeFIFO"; char read_fifo[] = "readFIFO";

//Check if the FIFO exists. If not, try to create it. if( access(write_fifo, F_OK)==-1 ){ int result = mkfifo(write_fifo, 0777); if( result!=0 ){ fprintf(stderr, "FIFO creation failed."); return 1; } } if( access(read_fifo, F_OK)==-1 ){ int result = mkfifo(read_fifo, 0777); if( result!=0 ){ fprintf(stderr, "FIFO creation failed."); return 1; } } int w_pipe = open(write_fifo, O_WRONLY); int r_pipe = open(read_fifo, O_RDONLY); if( w_pipe==-1 ){ fprintf(stderr, "Error opening %s\n", write_fifo); return 2; } if( r_pipe==-1 ){



fprintf(stderr, "Error opening %s\n", read_fifo); return 2; }

int bytes; char w_buffer[BUF_SIZE], r_buffer[BUF_SIZE];

do{ fprintf(stdout, "Enter something to be sent for PROCESSING :"); fgets(w_buffer, BUF_SIZE-1, stdin); w_buffer[strlen(w_buffer)-1] = '\0';

//Write the string into the pipe. bytes = write(w_pipe, w_buffer, strlen(w_buffer)); if( bytes<0 ) fprintf(stderr, "Error writing to pipe! Data lost??"); //Read string from pipe, after processing. memset(r_buffer, '\0', sizeof(r_buffer)); read(r_pipe, r_buffer, sizeof(r_buffer)); fprintf(stdout, "The string after processing is :%s\n", r_buffer); }while( strncmp(w_buffer, "quit", 4)!=0 );

close(w_pipe); close(r_pipe);

fprintf(stdout, "IO Handler Process finished [PID=%d]\n", (int)getpid() ); return 0;}

//Producer program produces items and writes to a FIFO. Consumer reads this FIFO and processes the items. The processed items are written to another FIFO. This is read by the producer.

GENERAL INSTRUCTIONS

For programs that are sender-receiver or client-server type(ftp, mac, smtp, ipc using sockets, messageQ, named pipes)g++ <sender.c> -o senderg++ <receiver.c> -o recv

then run in 2 terminals(always server/receiver first) as:./recv <port>./sender <IP> <port>

if its not a NW pgm(eg: msgQs, named pipes) just run as:



./recv

./sender

compiling RPC:

there are 3 files initially, which we code... finger.x, client.c, server.c

compile in the following order...

do this in both the client and server systems

rpcgen -C finger.x (thats a C, not c)gcc -c client.c -o clientgcc -c server.c -o servergcc -c finger_clnt.c -o f_cgcc -c finger_svc.c -o f_sgcc -c finger_xdr.c -o f_x

In the server system, do:gcc -o fs server f_s f_x

In the client system, do:gcc -o fc client f_c f_x

Now run as before,./fs <port>./fc <IP> <port>

For threaded programs, compile withg++ <program.cpp> -lpthread

For dining philosopher using ncurses lib, g++ dining.cpp -lpthread -lcursesif that doesn't workg++ -I/usr/include/ncurses dining.cpp -lpthread



NETWORKING



SOCKET PROGRAMMING

Theory

Sockets provide point-to-point, two-way communication between two processes.

Sockets are very versatile and are a basic component of interprocess and intersystem

communication. A socket is an endpoint of communication to which a name can be bound. It

has a type and one or more associated processes.

Sockets exist in communication domains. A socket domain is an abstraction that

provides an addressing structure and a set of protocols. Sockets connect only with sockets in

the same domain. Twenty three socket domains are identified (see <sys/socket.h>), of which

only the UNIX and Internet domains are normally used Solaris 2.x Sockets can be used to

communicate between processes on a single system, like other forms of IPC.

The UNIX domain provides a socket address space on a single system. UNIX domain

sockets are named with UNIX paths. Sockets can also be used to communicate between

processes on different systems. The socket address space between connected systems is

called the Internet domain.

Internet domain communication uses the TCP/IP internet protocol suite.

Socket types define the communication properties visible to the application.

Processes communicate only between sockets of the same type. There are five types of

socket.

A stream socket

-- provides two-way, sequenced, reliable, and unduplicated flow of data with no

record boundaries. A stream operates much like a telephone conversation. The socket



type is SOCK_STREAM, which, in the Internet domain, uses Transmission Control

Protocol (TCP).

A datagram socket

-- supports a two-way flow of messages. A on a datagram socket may receive

messages in a different order from the sequence in which the messages were sent.

Record boundaries in the data are preserved. Datagram sockets operate much like

passing letters back and forth in the mail. The socket type is SOCK_DGRAM, which,

in the Internet domain, uses User Datagram Protocol (UDP).

A sequential packet socket

-- provides a two-way, sequenced, reliable, connection, for datagrams of a fixed

maximum length. The socket type is SOCK_SEQPACKET. No protocol for this type

has been implemented for any protocol family.

A raw socket

provides access to the underlying communication protocols.

These sockets are usually datagram oriented, but their exact characteristics depend on the

interface provided by the protocol.

Socket Creation and Naming

int socket(int domain, int type, int protocol) is called to create a socket in the

specified domain and of the specified type. If a protocol is not specified, the system

defaults to a protocol that supports the specified socket type. The socket handle (a

descriptor) is returned. A remote process has no way to identify a socket until an address

is bound to it. Communicating processes connect through addresses. In the UNIX

domain, a connection is usually composed of one or two path names. In the Internet

domain, a connection is composed of local and remote addresses and local and remote

ports. In most domains, connections must be unique.

int bind(int s, const struct sockaddr *name, int namelen) is called to bind a path or

internet address to a socket. There are three different ways to call bind(), depending on

the domain of the socket.



For UNIX domain sockets with paths containing 14, or fewer characters, you can:

#include <sys/socket.h>

...

bind (sd, (struct sockaddr *) &addr, length);

If the path of a UNIX domain socket requires more characters, use:

#include <sys/un.h>

...

bind (sd, (struct sockaddr_un *) &addr, length);

For Internet domain sockets, use

#include <netinet/in.h>

...

bind (sd, (struct sockaddr_in *) &addr, length);

In the UNIX domain, binding a name creates a named socket in the file system. Use unlink()

or rm () to remove the socket.

Connecting Stream Sockets

Connecting sockets is usually not symmetric. One process usually acts as a server and the

other process is the client. The server binds its socket to a previously agreed path or address.

It then blocks on the socket. For a SOCK_STREAM socket, the server calls int listen(int s,

int backlog) , which specifies how many connection requests can be queued. A client initiates

a connection to the server's socket by a call to int connect(int s, struct sockaddr *name, int

namelen) . A UNIX domain call is like this:

struct sockaddr_un server;

...

connect (sd, (struct sockaddr_un *)&server, length);

while an Internet domain call would be:

struct sockaddr_in;

...



connect (sd, (struct sockaddr_in *)&server, length);

If the client's socket is unbound at the time of the connect call, the system automatically

selects and binds a name to the socket. For a SOCK_STREAM socket, the server calls

accept(3N) to complete the connection.

int accept(int s, struct sockaddr *addr, int *addrlen) returns a new socket descriptor which is

valid only for the particular connection. A server can have multiple SOCK_STREAM

connections active at one time.

Stream Data Transfer and Closing

Several functions to send and receive data from a SOCK_STREAM socket. These are

write(), read(), int send(int s, const char *msg, int len, int flags), and int recv(int s, char *buf,

int len, int flags). send() and recv() are very similar to read() and write(), but have some

additional operational flags.

The flags parameter is formed from the bitwise OR of zero or more of the following:

MSG_OOB

-- Send "out-of-band" data on sockets that support this notion. The underlying

protocol must also support "out-of-band" data. Only SOCK_STREAM sockets

created in the AF_INET address family support out-of-band data.

MSG_DONTROUTE

-- The SO_DONTROUTE option is turned on for the duration of the operation. It is

used only by diagnostic or routing programs.

MSG_PEEK

-- "Peek" at the data present on the socket; the data is returned, but not consumed, so

that a subsequent receive operation will see the same data.

A SOCK_STREAM socket is discarded by calling close().



Datagram sockets

A datagram socket does not require that a connection be established. Each message carries

the destination address. If a particular local address is needed, a call to bind() must precede

any data transfer. Data is sent through calls to sendto() or sendmsg(). The sendto() call is like

a send() call with the destination address also specified. To receive datagram socket

messages, call recvfrom() or recvmsg(). While recv() requires one buffer for the arriving

data, recvfrom() requires two buffers, one for the incoming message and another to receive

the source address.

Datagram sockets can also use connect() to connect the socket to a specified destination

socket. When this is done, send() and recv() are used to send and receive data.

accept() and listen() are not used with datagram sockets.

TRANSFER CONTROL PROTOCOL(TCP)

Server

Algorithm

The activity involved in a tcp server are.......... 1.Create a socket.

2.Bind it to the operating system.

3.Listen over it.

4.Accept connections.

5.Read/Write processes.

6.Close the socket.



Program

/*Program to demonstrate the creation and usage of tcp socket.

* This module acts as the tcp server which listens to a socket and accepts connection.

* The server initially reads a message from the client and then writes a message to it.

* This module should be compiled using the command. 'c++ tcpserver.cpp' and execute

'./a.out'.*/

//inculsion.#include<iostream>#include<stdio.h>

#include<sys/types.h>#include<netinet/in.h>#include<netdb.h>

int main(){

//variables to store the socket id. int serversocket,clientsocket;

//variables to store the network host addresses. sockaddr_in serveraddr,clientaddr;

//variable to store address length. socklen_t len; char message[50];

//creating a socket. serversocket=socket(AF_INET,SOCK_STREAM,0);

//steps to include the host address bzero((char*)&serveraddr,sizeof(serveraddr)); serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5030); serveraddr.sin_addr.s_addr=INADDR_ANY;

//binding the socket to the operating system. bind(serversocket,(sockaddr*)&serveraddr,sizeof(serveraddr));

bzero((char*)&clientaddr,sizeof(clientaddr)); len=sizeof(clientaddr);



//listening over the socket. listen(serversocket,5);

printf("\nWaiting for client connectivity.\n");

//accepting the connection. clientsocket=accept(serversocket,(sockaddr*)&clientaddr,&len);

printf("\nClient connectivity received.\n");

printf("\nReading message from the client.\n");

//reading activity. read(clientsocket,message,sizeof(message));

printf("\nThe client has send:\t%s\n",message);

printf("\nSending message to the client.\n");

//writing activity. write(clientsocket,"YOUR MESSAGE RECEIVED.",sizeof("YOUR MESSAGE RECEIVED."));

close(clientsocket); close(serversocket);}

Output



Client

Algorithm

The different processes involved in a udp client process are........

1.Create a datagram socket.

2.Receive/Send message to the server.

3.Close the socket.

Program

/* Program to demonstrate the creation and usage of datagram sockets.

* This module acts as a udp client which sends and receives messages from a udp server.

* This module should be compiled into different folder using the command 'c++

udpclient.cpp -o b' and execute using './b'

* For execution the 'udpserver' module should be executed first then this module.



int main(){

//variable to store the socket_id. int clientsocket;

//variable to store the address. sockaddr_in serveraddr;

//variableto store the address length. socklen_t len;

//variable to store the network byte order address. hostent *server; char message[50];

//socket creation.



clientsocket=socket(AF_INET,SOCK_DGRAM,0);//steps involved in the server address creation.

bzero((char*)&serveraddr,sizeof(serveraddr)); len=sizeof(serveraddr); serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5015); server=gethostbyname("127.0.0.1"); bcopy((char*)server->h_addr,(char*)&serveraddr.sin_addr.s_addr,sizeof(server->h_addr)); printf("\nPRESS ENTER TO START THE CONNECTION PROCESS.\n"); fgets(message,2,stdin);

printf("\nSending message for server connection\n");//sending message.

sendto(clientsocket,"HI I AM CLIENT...",sizeof("HI I AM CLIENT...."),0,(sockaddr*)&serveraddr,sizeof(serveraddr)); printf("\nReceiving message from server.\n");

//receiving messages. recvfrom(clientsocket,message,sizeof(message),0,(sockaddr*)&serveraddr,&len);

printf("\nMessage received:\t%s\n",message);

close(clientsocket);}

Output



USER DATAGRAM PROTOCOL(UDP)

Server

Algorithm

* The different process involved in an udp server process are.......


2.Bind the socket to the operating system.

3.Receive/Sending processes.

4.Close the socket.

Program

/* Program to demonstrate the creation and use of datagram socket.

* This module act as udp server which waits for client connection

* This server initially receives message from the client and then sends back a reply.

* This module should be comipled using the command 'c++ tcpserver.cpp' and execute './a.out'.



int main(){

//variable to store the socket_id. int serversocket;

//variable to store the network addresses. sockaddr_in serveraddr,clientaddr;



//variable to store the address length. socklen_t len; char message[50];

//socket creation. serversocket=socket(AF_INET,SOCK_DGRAM,0);

//steps involved in defining the serveraddress. bzero((char*)&serveraddr,sizeof(serveraddr)); serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5015); serveraddr.sin_addr.s_addr=INADDR_ANY;

//binding the socket to the operating system. bind(serversocket,(sockaddr*)&serveraddr,sizeof(serveraddr));

printf("\nWaiting for the client connection\n");


//receiving message from the client. recvfrom(serversocket,message,sizeof(message),0,(sockaddr*)&clientaddr,&len);

printf("\nConnection received from client.\n");

printf("\nThe client has send:\t%s\n",message);

printf("\nSending message to the client.\n");

//sending message to the client. sendto(serversocket,"YOUR MESSAGE RECEIVED.",sizeof("YOUR MESSAGE RECEIVED."),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

close(serversocket);}

Output



Client

Algorithm

* The different processes involved in a udp client process are........


2.Receive/Send message to the server.

3.Close the socket.

Program

/* Program to demonstrate the creation and usage of datagram sockets.

* This module acts as a udp client which sends and receives messages from a udp server.

* This module should be compiled into different folder using the command 'c++ udpclient.cpp -o b' and execute using './b'

* For execution the 'udpserver' module should be executed first then this module.

//inculsion.#include<iostream>#include<stdio.h>#include<sys/types.h>



#include<netinet/in.h>#include<netdb.h>

int main(){

//variable to store the socket_id. int clientsocket;

//variable to store the address. sockaddr_in serveraddr;

//variableto store the address length. socklen_t len;

//variable to store the network byte order address. hostent *server; char message[50];

//socket creation. clientsocket=socket(AF_INET,SOCK_DGRAM,0);

//steps involved in the server address creation. bzero((char*)&serveraddr,sizeof(serveraddr)); len=sizeof(serveraddr); serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5015); server=gethostbyname("127.0.0.1"); bcopy((char*)server->h_addr,(char*)&serveraddr.sin_addr.s_addr,sizeof(server->h_addr)); printf("\nPRESS ENTER TO START THE CONNECTION PROCESS.\n"); fgets(message,2,stdin); printf("\nSending message for server connection\n");

//sending message. sendto(clientsocket,"HI I AM CLIENT...",sizeof("HI I AM CLIENT...."),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

printf("\nReceiving message from server.\n");

//receiving messages. recvfrom(clientsocket,message,sizeof(message),0,(sockaddr*)&serveraddr,&len);

printf("\nMessage received:\t%s\n",message);


Output





MACPROTOCOLS

Theory

The Media Access Control (MAC) data communication protocol sub-layer, also

known as the Medium Access Control, is a part of the data link layer specified in the seven-

layer OSI model (layer 2). It provides addressing and channel access control mechanisms that

make it possible for several terminals or network nodes to communicate within a multipoint

network, typically a local area network (LAN) or metropolitan area network (MAN). A MAC

protocol is not required in full-duplex point-to-point communication. In single channel point-

to-point communications full-duplex can be emulated. This emulation can be considered a

MAC layer.

The MAC sub-layer acts as an interface between the Logical Link Control sublayer

and the network's physical layer.

The MAC layer provides an addressing mechanism called physical address or MAC

address. This is a unique serial number assigned to each network adapter, making it possible

to deliver data packets to a destination within a subnetwork, i.e. a physical network without

routers, for example an Ethernet network.

Media access control is often used as a synonym to multiple access protocol, since the MAC

sublayer provides the protocol and control mechanisms that are required for a certain channel

access method. This makes it possible for several stations connected to the same physical

medium to share it. Examples of shared physical medium are bus networks, ring networks,

hub networks, wireless networks and half-duplex point-to-point links.

SLIDING WINDOW PROTOCOL


http://en.wikipedia.org/wiki/Half-duplex

http://en.wikipedia.org/wiki/Wireless_networks

http://en.wikipedia.org/wiki/Hub_network

http://en.wikipedia.org/wiki/Ring_network

http://en.wikipedia.org/wiki/Bus_network

http://en.wikipedia.org/wiki/Physical_medium

http://en.wikipedia.org/wiki/Physical_medium

http://en.wikipedia.org/wiki/Channel_access_method

http://en.wikipedia.org/wiki/Channel_access_method

http://en.wikipedia.org/wiki/Multiple_access

http://en.wikipedia.org/wiki/Router

http://en.wikipedia.org/wiki/Subnetwork

http://en.wikipedia.org/wiki/Network_adapter

http://en.wikipedia.org/wiki/MAC_address

http://en.wikipedia.org/wiki/MAC_address

http://en.wikipedia.org/wiki/Physical_layer

http://en.wikipedia.org/wiki/Logical_Link_Control

http://en.wikipedia.org/wiki/Duplex_(telecommunications)#Emulation_of_full_duplex_in_shared_physical_media

http://en.wikipedia.org/wiki/Point-to-point

http://en.wikipedia.org/wiki/Full-duplex

http://en.wikipedia.org/wiki/Metropolitan_area_network

http://en.wikipedia.org/wiki/Local_area_network

http://en.wikipedia.org/wiki/Terminal_(telecommunication)

http://en.wikipedia.org/wiki/Channel_access

http://en.wikipedia.org/wiki/Seven-layer_OSI_model

http://en.wikipedia.org/wiki/Seven-layer_OSI_model

http://en.wikipedia.org/wiki/Data_link_layer

http://en.wikipedia.org/wiki/Data_communication_protocol


In the simplex, stop and wait protocols, data frames were transmitted

in one direction only. In most practical solutions, there is a need for transmitting data in both

directions. One way of achieving full-duplex data transmission is to have two separate

communication channels and use each one for simplex data traffic. If this is done, we have

two separate physical circuits, each with a “forward” channel (for data) and a” reverse”

channel (for acknowledgements).In both cases the bandwidth of the reverse channel is almost

wasted.

A better idea is to use same circuit for data in both directions. In this model data

frames from A to B are intermixed with the acknowledgement frames from A to B.By

looking at the kind field in the header of an incoming frame, the receiver can tell whether the

frame is data or acknowledgement. When a data frame arrives, instead of immediately

sending a separate control frame, the receiver retrains itself and waits until the network layer

passes it the next packet. The acknowledgement is attached to the outgoing data frame. The

technique of temporarily delaying outgoing acknowledgements so that they can be hooked

onto the next outgoing data frame known as piggybacking. The principal advantage of using

piggybacking over having distinct acknowledgement frames is a better use of the available

channel bandwidth.

Bidirectional protocols that belongs to a class called sliding window

protocols. They differ among themselves in terms of efficincy, complexity,and buffer

requirements. All sliding window protocols ,each outbound frame contains a sequence

number ,ranging from 0 up to some maximum. The essence of all sliding window protocols

is that at any instant of time ,the sender maintains a set of sequence numbers corresponding

to frames it is permitted to send . These frames are said to fall within the sending window,

the receiver also maintains a receiving window corresponding to the set of frames it is

permitted to accept.

A One- Bit Sliding Window Protocol

A sliding window protocol with a maximum window size of 1.Such a

protocol uses a stop-and-wait since the sender transmits a frame and waits for its

acknowledgement before sending the next one. The starting machine fetches the first packet



from its network layer, builds a frame from it, and sends it. The acknowledgement field

contains the number of the last frame received without error. If this number agrees with the

sequence number of the frame the sender is trying to send ,the sender knows it is done with

the frame stored in buffer and can fetch the next packet from its network layer. If the

sequence number disagrees, it must continue trying to send the same frame Whenever a

frame is received, a frame also sent back.

A Protocol Using Go Back N

Two basic approaches are available for dealing with errors in the

presence of pipelining. One way, called go back n ,is for the receiver simply to discard all

subsequent frames ,sending no acknowledgements for the discarded frames. In other words,

the data link layer refuses to accept any frame except the next one it must give to the network

layer

A Protocol Using Selective Repeat

In this protocol, both sender and receiver maintain a window of acceptable

sequence numbers. The sender’s window size starts out at 0 and grows to some predefined

maximum. The receiver’s window, in contrast, is always fixed in size and equal to maximum.

The receiver has a buffer reserved for each sequence number within its fixed window.

Whenever a frame arrives, its sequence number is checked by the function between to see if

falls within the window. If so and if it has not already been received, it is accepted and

stroed.This action is taken without regard to whether or not it contains the next packet

expected by the network layer.



GOBACKN PROTOCOLS

Server

Algorithm

* The algorithm for this process is as............................

1. Start.

2. Establish connection (recommended UDP)

3. Accept the window size from the client(should be <=40)

4. Accept the packets from the network layer.

5. Calculate the total frames/windows required.

6. Send the details to the client(totalpackets,totalframes.)

7. Initialise the transmit buffer.

8. Built the frame/window depending on the windowsize.

9. Transmit the frame.

10. Wait for the acknowledgement frame.

11. Check for the acknowledgement of each packet and repeat the process

from the packet for which the first negative acknowledgement is

received.

Else continue as usual.

12. Increment the framecount and repeat steps 7 to 12 until all packets are

transmitted.

13. Close the connection.

14. Stop.



Program

/* Program to demonstrate the working of 'GO BACK N PROTOCOL'.

* This module act as a server which initially establishes a connection with the client,

sends packets to it (using sliding window protocol),receives acknowledgement and

retransmits the packets for which negative acknowledgement is received (using go

back n protocol).

* It uses an UDP connection for the whole process.

* It uses two structures viz. 'frame' to design the frames/window to be transmitted and

'ack' to accept the acknowledgement.

* Here -1 is referred to as negative acknowledgement while all the other integers as

positive acknwoledgement.

* The initial process are similar to that defined in the sliding window server process.

//inculsion#include<iostream>#include<stdio.h>


#define cls() printf("\033[H\033[J")

//structure definition for designing the packet.struct frame{ int packet[40];};

//structure definition for accepting the acknowledgement.struct ack{ int acknowledge[40];};

int main(){



int serversocket; sockaddr_in serveraddr,clientaddr; socklen_t len; int windowsize,totalpackets,totalframes,framessend=0,i=0,j=0,k,buffer,l; ack acknowledgement; frame f1; char req[50];

serversocket=socket(AF_INET,SOCK_DGRAM,0);

bzero((char*)&serveraddr,sizeof(serveraddr)); serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5018); serveraddr.sin_addr.s_addr=INADDR_ANY;

bind(serversocket,(sockaddr*)&serveraddr,sizeof(serveraddr));


//connection establishment. printf("\nWaiting for client connection.\n"); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len); printf("\nThe client connection obtained.\t%s\n",req);

//sending request for windowsize. printf("\nSending request for window size.\n"); sendto(serversocket,"REQUEST FOR WINDOWSIZE.",sizeof("REQUEST FOR WINDOWSIZE."),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//obtaining windowsize. printf("\nWaiting for the windowsize.\n"); recvfrom(serversocket,(char*)&windowsize,sizeof(windowsize),0,(sockaddr*)&clientaddr,&len); cls(); printf("\nThe windowsize obtained as:\t%d\n",windowsize);

printf("\nObtaining packets from network layer.\n"); printf("\nTotal packets obtained:\t%d\n",(totalpackets=windowsize*5)); printf("\nTotal frames or windows to be transmitted:\t%d\n",(totalframes=5));

//sending details to client. printf("\nSending total number of packets.\n"); sendto(serversocket,(char*)&totalpackets,sizeof(totalpackets),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len);



printf("\nSending total number of frames.\n"); sendto(serversocket,(char*)&totalframes,sizeof(totalframes),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len); printf("\nPRESS ENTER TO START THE PROCESS.\n"); fgets(req,2,stdin); cls();

//starting the process of sending while( i<totalpackets) {

//initialising the transmit buffer. bzero((char*)&f1,sizeof(f1)); printf("\nInitialising the transmit buffer.\n"); printf("\nThe frame to be send is %d with packets:\t",framessend); buffer=i; j=0;

//Builting the frame. while(j<windowsize && i<totalpackets) { printf("%d ",i); f1.packet[j]=i; i++; j++; } printf("\nSending frame %d\n",framessend);

//sending the frame. sendto(serversocket,(char*)&f1,sizeof(f1),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//Waiting for the acknowledgement. printf("\nWaiting for the acknowledgement.\n"); recvfrom(serversocket,(char*)&acknowledgement,sizeof(acknowledgement),0,(sockaddr*)&clientaddr,&len); cls();

//Checking acknowledgement of each packet. j=0; k=0; l=buffer; while(j<windowsize && l<totalpackets) { if(acknowledgement.acknowledge[j]==-1) { printf("\nNegative acknowledgement received for packet: %d\n",f1.packet[j]);



printf("\nRetransmitting from packet: %d.\n",f1.packet[j]); i=f1.packet[j]; k=1; break; } j++; l++; }

if(k==0) { printf("\nPositive acknowledgement received for all packets within the frame: %d\n",framessend); }

framessend++; printf("\nPRESS ENTER TO PROCEED......\n"); fgets(req,2,stdin); cls(); }

printf("\nAll frames send successfully.\n\nClosing connection with the client.\n"); close(serversocket);}

Output



Client

Algorithm

* The algorithm for this module process is as........................

1. Start.

2. Establish a connection.(recommended UDP)

3. Send the windowsize on server request.

4. Accept the details from the server(totalpackets,totalframes).

5. Initialise the receive buffer with the expected packets.

6. Accept the frame/window from the server.

7. Check for validity of the packets and construct the acknowledgement

frame depending on the validity.(Here the acknowledgement is

accepeted from the users)

8. Depending on the acknowledgement frame readjust the process.



9. Increment the framecount and repeat steps 5-9 until all

packets are received.


11. Stop.

Program

/* Program to demonstrate the working of 'GO BACK N PROTOCOL'.

* This module acts as a client which establishes a connection with the server, sends the

window size , accepts the frames and then sends acknowledgement for each packet

within the given frame.

* The connection used is UDP and the window size is taken from the user(should

be<=40)

* It uses two structures viz. 'frame' for accepting the frames send by the server and 'ack'

for sending the acknowledgement.

* Here the acknowledgement for each packet is accepted from the user. The user can

enter -1 for negative acknowledgement or any other integer for positive

acknowledgement.

* NOTE:-> This module can be compiled using the command 'c++ gobackn_server.cpp -o b'

and executed using the command './b'

Always compile and execute the server module first.

//inclusion.#include<iostream>#include<stdio.h>





//structure definition for accepting the packets.struct frame{ int packet[40];};

//structure definition for constructing the acknowledgement framestruct ack{ int acknowledge[40];};

int main(){ int clientsocket; sockaddr_in serveraddr; socklen_t len; hostent * server; frame f1; int windowsize,totalpackets,totalframes,i=0,j=0,framesreceived=0,k,buffer,l; ack acknowledgement; char req[50];

clientsocket=socket(AF_INET,SOCK_DGRAM,0);

bzero((char*)&serveraddr,sizeof(serveraddr)); serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5018); server=gethostbyname("127.0.0.1"); bcopy((char*)server->h_addr,(char*)&serveraddr.sin_addr.s_addr,sizeof(server->h_addr));

//establishing the connection. printf("\nSending request to the client.\n"); sendto(clientsocket,"HI I AM CLIENT.",sizeof("HI I AM CLIENT."),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

printf("\nWaiting for reply.\n"); recvfrom(clientsocket,req,sizeof(req),0,(sockaddr*)&serveraddr,&len); printf("\nThe server has send:\t%s\n",req);

//accepting window size from the user. printf("\nEnter the window size:\t"); scanf("%d",&windowsize);

//sending the window size. printf("\n\nSending the window size.\n");



sendto(clientsocket,(char*)&windowsize,sizeof(windowsize),0,(sockaddr*)&serveraddr,sizeof(serveraddr)); cls();

//collecting details from server. printf("\nWaiting for the server response.\n"); recvfrom(clientsocket,(char*)&totalpackets,sizeof(totalpackets),0,(sockaddr*)&serveraddr,&len); printf("\nThe total packets are:\t%d\n",totalpackets); sendto(clientsocket,"RECEIVED.",sizeof("RECEIVED."),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

recvfrom(clientsocket,(char*)&totalframes,sizeof(totalframes),0,(sockaddr*)&serveraddr,&len); printf("\nThe total frames/windows are:\t%d\n",totalframes); sendto(clientsocket,"RECEIVED.",sizeof("RECEIVED."),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

//starting the process. printf("\nStarting the process of receiving.\n"); while(i<totalpackets) {

//initialising the receive buffer. printf("\nInitialising the receive buffer.\n"); printf("\nThe expected frame is %d with packets: ",framesreceived); j=0; buffer=i; while(j<windowsize && i<totalpackets) { printf("%d ",i); i++; j++; }

printf("\n\nWaiting for the frame.\n");//accepting the frame.

recvfrom(clientsocket,(char*)&f1,sizeof(f1),0,(sockaddr*)&serveraddr,&len); printf("\nReceived frame %d\n\nEnter -1 to send negative acknowledgement for the following packets.\n",framesreceived);

//constructing the acknowledgement frame. j=0; l=buffer; k=0; while(j<windowsize && l<totalpackets) {



printf("\nPacket: %d\n",f1.packet[j]); //accepting acknowledgement from the user.

scanf("%d",&acknowledgement.acknowledge[j]);

if(acknowledgement.acknowledge[j]==-1) { if(k==0) { i=f1.packet[j]; k=1; } } j++; l++; } framesreceived++;

//sending acknowledgement to the server. sendto(clientsocket,(char*)&acknowledgement,sizeof(acknowledgement),0,(sockaddr*)&serveraddr,sizeof(serveraddr)); cls(); }

printf("\nAll frames received successfully.\n\nClosing connection with the server.\n"); close(clientsocket);}

Output





SELECTIVE REPEAT REQUEST PROTOCOL

Server

Algorithm

* The algorithm for this process is as............................

1. Start.

2. Establish connection (recommended UDP)

3. Accept the window size from the client(should be <=40)

4. Accept the packets from the network layer.

5. Calculate the total frames/windows required.

6. Send the details to the client(totalpackets,totalframes.)

7. Initialise the transmit buffer.

8. Built the frame/window depending on the windowsize.



9. Transmit the frame.

10. Wait for the acknowledgement frame.

11. Check for the acknowledgement of each packet and repeat the

process for the packet for which the negative acknowledgement isreceived.

Else continue as usual.

12. Increment the frame count and repeat steps 7 to 12 until all packets are

transmitted.


14.Stop.

Program

/* Program to demonstrate the working of 'SELECTIVE REPEAT PROTOCOL'.

* This module act as a server which initially establishes a connection with the client, sends

packets to it (using sliding window protocol),receives acknowledgement and retransmits

the packets for which negative acknowledgement is received (using selective repeat

protocol).

* It uses an UDP connection for the whole process.

* It uses two structures viz. 'frame' to design the frames/window to be transmitted and

'ack' to accept the acknowledgement.

* Here -1 is referred to as negative acknowledgement while all the other integers as

positive acknowledgement.

* The initial process are similar to that defined in the sliding window server process.

* NOTE: -> This module can be compiled using the command 'c++

selectiverepeat_server.cpp' and executed using './a.out'

-> The server module should be compiled and executed first.






//structure definition for designing the packet.struct frame{ int packet[40];};

//structure definition for accepting the acknowledgement.struct ack{ int acknowledge[40];};

int main(){ int serversocket; sockaddr_in serveraddr,clientaddr; socklen_t len; int windowsize,totalpackets,totalframes,framessend=0,i=0,j=0,k,l,m,n,repacket[40]; ack acknowledgement; frame f1; char req[50];




bzero((char*)&clientaddr,sizeof(clientaddr));



len=sizeof(clientaddr);





//sending details to client. printf("\nSending total number of packets.\n"); sendto(serversocket,(char*)&totalpackets,sizeof(totalpackets),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len); printf("\nSending total number of frames.\n"); sendto(serversocket,(char*)&totalframes,sizeof(totalframes),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len); printf("\nPRESS ENTER TO START THE PROCESS.\n"); fgets(req,2,stdin); cls();

j=0; l=0; //starting the process of sending while( l<totalpackets) {

//initialising the transmit buffer. bzero((char*)&f1,sizeof(f1)); printf("\nInitialising the transmit buffer.\n"); printf("\nThe frame to be send is %d with packets:\t",framessend);

//Builting the frame.



for(m=0;m<j;m++) {

//including the packets for which negative acknowledgement was received. printf("%d ",repacket[m]); f1.packet[m]=repacket[m]; }

while(j<windowsize && i<totalpackets) { printf("%d ",i); f1.packet[j]=i; i++; j++; } printf("\nSending frame %d\n",framessend);

//sending the frame. sendto(serversocket,(char*)&f1,sizeof(f1),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//Waiting for the acknowledgement. printf("\nWaiting for the acknowledgement.\n"); recvfrom(serversocket,(char*)&acknowledgement,sizeof(acknowledgement),0,(sockaddr*)&clientaddr,&len); cls();

//Checking acknowledgement of each packet. j=0; k=0; m=0; n=l; while(m<windowsize && n<totalpackets) { if(acknowledgement.acknowledge[m]==-1) { printf("\nNegative acknowledgement received for packet: %d\n",f1.packet[m]); k=1; repacket[j]=f1.packet[m]; j++; } else { l++; } m++; n++; }

if(k==0)



{ printf("\nPositive acknowledgement received for all packets within the frame: %d\n",framessend); }

framessend++; printf("\nPRESS ENTER TO PROCEED......\n"); fgets(req,2,stdin); cls(); }


Output



Client

Algorithm

* The algorithm for this module process is as........................

1. Start.

2. Establish a connection.(recommended UDP)

3. Send the windowsize on server request.

4. Accept the details from the server(totalpackets,totalframes).

5. Initialise the receive buffer with the expected packets.

6. Accept the frame/window from the server.

7. Check for validity of the packets and construct the acknowledgement frame

depending on the validity.(Here the acknowledgement is accepeted from the

users)



8. Depending on the acknowledgement frame readjust the process.

9. Increment the framecount and repeat steps 5-9 until all packets are received.


11. Stop.

Program

/* Program to demonstrate the working of 'SELECTIVE REPEAT PROTOCOL'.

* This module acts as a client which establishes a connection with the server, sends the

windowsize, accepts the frames and then sends acknowledgement for each packet wihin

the given frame.

* The connection used is UDP and the window size is taken from the user(should be<=40)

* It uses two structures viz. 'frame' for accepting the frames send by the server and 'ack' for

sending the acknowledgement.

* Here the acknowledgement for each packet is accepted from the user. The user can enter -1

for negative acknowledgement or any other integer for positive acknowledgement.

* NOTE: This module can be compiled using the command 'c++ selectiverepeat_server.cpp –

o b' and executed using the command './b'

-> Always compile and execute the server module first.




//structure definition for accepting the packets.struct frame{ int packet[40];



};

//structure definition for constructing the acknowledgement framestruct ack{ int acknowledge[40];};

int main(){ int clientsocket; sockaddr_in serveraddr; socklen_t len; hostent * server; frame f1; int windowsize,totalpackets,totalframes,i=0,j=0,framesreceived=0,k,l,m,repacket[40]; ack acknowledgement; char req[50];



//establishing the connection. printf("\nSending request to the client.\n"); sendto(clientsocket,"HI I AM CLIENT.",sizeof("HI I AM CLIENT."),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

printf("\nWaiting for reply.\n"); recvfrom(clientsocket,req,sizeof(req),0,(sockaddr*)&serveraddr,&len); printf("\nThe server has send:\t%s\n",req);

//accepting window size from the user. printf("\nEnter the window size:\t"); scanf("%d",&windowsize);

//sending the window size. printf("\n\nSending the window size.\n"); sendto(clientsocket,(char*)&windowsize,sizeof(windowsize),0,(sockaddr*)&serveraddr,sizeof(serveraddr)); cls();





//starting the process. printf("\nStarting the process of receiving.\n"); j=0; l=0; while(l<totalpackets) {

//initialising the receive buffer. printf("\nInitialising the receive buffer.\n"); printf("\nThe expected frame is %d with packets: ",framesreceived); for(m=0;m<j;m++) {

//readjusting for packets with negative acknowledgement. printf("%d ",repacket[m]); } while(j<windowsize && i<totalpackets) { printf("%d ",i); i++; j++; }

printf("\n\nWaiting for the frame.\n");//accepting the frame.

recvfrom(clientsocket,(char*)&f1,sizeof(f1),0,(sockaddr*)&serveraddr,&len); printf("\nReceived frame %d\n\nEnter -1 to send negative acknowledgement for the following packets.\n",framesreceived);

//constructing the acknowledgement frame. j=0; m=0; k=l;



while(m<windowsize && k<totalpackets) { printf("\nPacket: %d\n",f1.packet[m]);

//accepting acknowledgement from the user. scanf("%d",&acknowledgement.acknowledge[m]);

if(acknowledgement.acknowledge[m]==-1) { repacket[j]=f1.packet[m]; j++; } else { l++; } m++; k++; } framesreceived++;

//sending acknowledgement to the server. sendto(clientsocket,(char*)&acknowledgement,sizeof(acknowledgement),0,(sockaddr*)&serveraddr,sizeof(serveraddr)); cls(); }


Output



SLIDING WINDOW PROTOCOL



Server

Algorithm

* The algorithm for the sliding window server is as..........

1.Start

2.Establish connection with the client.(UDP/TCP recommended UDP)

3.Accept the window size from the client.

4.Accept the packets from the network layer.

5.Combine packets to form frame/window.(depending on window size.)

6.Initialise the transmit buffer.

7.Send the frame and wait for the acknowledgement.

8.If a negative acknowledgement is received repeat the transmission of the

previous frame.

Else increment the frame to be transmitted.

9.Repeat steps 5 to 8 until all packet are transmitted successfully.

10.Close the connection.

11.Stop.

Program

/* Program to demonstrate the working of 'SLIDING WINDOW PROTOCOL'

* This module act as a server module which transmits the packets to the client.

* The server initially establishes connection with the client then accepts the window

size(should be always<=40).

* Then it calculates the total no. of packets by multiplying the window size with 5

(assumption: totalpackets=windowsize*5).

* Then frames are prepared depending upon the window size,transmits it to the client and

waits for the acknowledgement.

* If a negative (-1) acknowledgement is received the frame is transmitted again, else the next



frame is transmitted.

NOTE: Here only a single acknowledgement is considered for all the packets within a given

frame.

*NOTE: -> Compile this module using the command 'c++

slidingwindowserver.cpp'. To execute use './a.out'.

-> Compile and execute the server module first.

//inclusion.#include<iostream>#include<stdio.h>



//structure definition for defining the frame.struct frame{ int packet[40];};

int main(){ int serversocket; sockaddr_in serveraddr,clientaddr; socklen_t len; int windowsize,totalpackets,totalframes,framessend=0,i=0,j=0,buffer,acknowledgement; frame f1; char req[50];











//sending details to client. printf("\nSending total number of packets.\n"); sendto(serversocket,(char*)&totalpackets,sizeof(totalpackets),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len); printf("\nSending total number of frames.\n"); sendto(serversocket,(char*)&totalframes,sizeof(totalframes),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); recvfrom(serversocket,req,sizeof(req),0,(sockaddr*)&clientaddr,&len); printf("\nPRESS ENTER TO START THE PROCESS.\n"); fgets(req,2,stdin); cls();

//starting the process of sending while(framessend<totalframes) { printf("\nInitialising the transmit buffer.\n"); printf("\nThe frame to be send is %d with packets:\t",framessend); j=0; buffer=i;

//preparing the frame. while(j<windowsize && i<totalpackets) {



printf("%d ",i); f1.packet[j]=i; i++; j++; } printf("\nSending frame %d\n",framessend);

//sending frame. sendto(serversocket,(char*)&f1,sizeof(f1),0,(sockaddr*)&clientaddr,sizeof(clientaddr)); printf("\nWaiting for the acknowledgement.\n");

//waiting for the acknowledgement. recvfrom(serversocket,(char*)&acknowledgement,sizeof(int),0,(sockaddr*)&clientaddr,&len); cls();

//cheching the acknowledgement. if(acknowledgement==-1) { printf("\nNegative acknowledgement received for frame %d\n",framessend); printf("\nRetransmitting the frame.\n"); i=buffer; }

else { printf("\nPositive acknowledgement received for frame %d.\n",framessend); framessend++; } printf("\nPRESS ENTER TO PROCEED......\n"); fgets(req,2,stdin); cls(); }


Output



Client

Algorithm



* The algorithm for the client process is as............

1.Start.

2.Establish a connection with the server.(recommended UDP.)

3.Send the window size on server request.

4.Accept the details from the server.(totalpackets,totalframes.)

5.Initialise the receive buffer with the expected frame and packets.

6.Accept the frame and check for its validity.

7.Send positive or negative acknowledgement as required.

8.Repeat steps 5 to 7 until all packets are received.

9.Close the connection with the server.

10.Stop.

Program

/* Program to demonstrate the working of 'SLIDING WINDOW PROTOCOL.'

* This module act as client which accepts the packets from the server.

* The client initially establishes a connection with the server and then on request from the server sends the window size to the server.

NOTE: Here the window size is taken from the user. The user can input any valid number <=40.

* It also collects details such as the total packets and total frames from the server.

* It then receives the frames from the server for which it sends acknowledgement.

NOTE: Here the acknowledgement is accepted from the user. The user can input -1 for negative acknowledgement and 1 or any other number for positive acknowledgement.




#include<sys/types.h>#include<netinet/in.h>#include<netdb.h>#define cls() printf("\033[H\033[J")

//structure definition for accepting the frame.struct frame{ int packet[40];};

int main(){ int clientsocket; sockaddr_in serveraddr; socklen_t len; hostent * server; frame f1; int windowsize,totalpackets,totalframes,i=0,j=0,framesreceived=0,acknowledgement,buffer; char req[50];



printf("\nSending request to the client.\n"); sendto(clientsocket,"HI I AM CLIENT.",sizeof("HI I AM CLIENT."),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

//accepting the window request. printf("\nWaiting for reply.\n"); recvfrom(clientsocket,req,sizeof(req),0,(sockaddr*)&serveraddr,&len); printf("\nThe server has send:\t%s\n",req);

//taking the window size from the user. printf("\nEnter the window size:\t"); scanf("%d",&windowsize);

//sending the window size. printf("\n\nSending the window size.\n"); sendto(clientsocket,(char*)&windowsize,sizeof(windowsize),0,(sockaddr*)&serveraddr,sizeof(serveraddr));



cls();



//starting the process. printf("\nStarting the process of receiving.\n"); while(framesreceived<totalframes) {

//initialising the receive buffer. printf("\nInitialising the receive buffer.\n"); printf("\nThe expected frame is %d with packets: ",framesreceived); j=0; buffer=i; while(j<windowsize && i<totalpackets) { printf("%d ",i); i++; j++; }

printf("\n\nWaiting for the frame.\n");

//receiving the frame. recvfrom(clientsocket,(char*)&f1,sizeof(f1),0,(sockaddr*)&serveraddr,&len); printf("\nReceived frame %d\n\nEnter -1 to send negative acknowledgement\n",framesreceived);

//taking acknowledgement from the user. scanf("%d",&acknowledgement); if(acknowledgement==-1) { i=buffer; } else {



framesreceived++; }

//sending acknowledgement to the server. sendto(clientsocket,(char*)&acknowledgement,sizeof(int),0,(sockaddr*)&serveraddr,sizeof(serveraddr)); cls(); }


Output



FILE TRANSFER PROTOCOL

Theory



The FTP protocol is used to access files by FTP, the internet”s file transfer protocol.

Ftp has been around more than two decades and is well entrenched. Numerous FTP servers

all over the world allow people anywhere on the internet to log in and download whatever

files have been placed on the FTP server. The Web does not change this; it just makes

obtaining files by FTP easier, as FTP has a somewhat arcane interface.

It is possible to access a local file as a web page, either by using the file protocol or

more simply by just naming it. This approach is similar to using FTP but does not require

having a server. Of course, it works only for files not remote ones.

Server

Algorithm

* The algorithm for ftp server can be summerised as...................

1. Start.

2. Establish a tcp socket.

3. Listen over the socket.

4. Accept a connection.

5. Obtain the filename from the client.

6. Read the file.

7. Send it to the client.


9. Stop.

Program

/* Program to demonstrate the implementation of ftp protocol.

* This module act as a ftp module, which accepts the filename, reads the file and sends it to



the client.

* This module establishes a tcp connection with the client.

* NOTE:

1. The file to be transfered should be in the same directory where this module is stored.

2. If the file does not exist the program might terminate abnormally.

3. The error handling routine has not been provided. It is assumed that everything would be

perfect.

* This program can be compiled using 'c++ simpleftpserver.cpp' and executed './a.out'

//inculsion.#include<iostream>#include<stdio.h>#include<string.h>


int main(){ int serversocket,clientsocket; sockaddr_in serveraddr,clientaddr; socklen_t len; FILE *ptr; char filename[20]; char file[2048],temp[500];

bzero(filename,sizeof(filename)); bzero(file,sizeof(file));

serversocket=socket(AF_INET,SOCK_STREAM,0);



bzero((char*)&clientaddr,sizeof(clientaddr));



len=sizeof(clientaddr);

listen(serversocket,5); printf("\nWaiting for the connection\n"); clientsocket=accept(serversocket,(sockaddr*)&clientaddr,&len); printf("\nConnection obtained.\n");

read(clientsocket,filename,sizeof(filename));

printf("\nThe read filename is:\t%s\n",filename); printf("\nReading the file.\n");

ptr=fopen(filename,"r"); while(fgets(temp,sizeof(temp),ptr)!=NULL) { strcat(file,temp); } fclose(ptr);

printf("\nSending the file.\n"); write(clientsocket,file,sizeof(file));

close(clientsocket); close(serversocket);}

Output



Client

Algorithm

* The algorithm for the process can be summerised as...............

1. Start.

2. Establish a tcp connection.

3. Connect to the ftp server.

4. Send the filename.

5. Read the filecontents.

6. Create a file as required.


8. Stop.

Program

/* Program to demonstrate the implementation of ftp protocol.

* This module act as the ftp client which sends the filename and receives the file from the

server.

* This module is designed with a view to represent the ftp process with simplicity, so it only

sends and receives data.



* It can be compiled using 'c++ simpleftpclient.cpp -o b' and executed './b'

#include<iostream>#include<stdio.h>


#define FILENAME "sample.c"

int main(){ int clientsocket; sockaddr_in serveraddr; hostent * server; FILE * ptr; char file[2048];

bzero(file,sizeof(file));

clientsocket=socket(AF_INET,SOCK_STREAM,0);

bzero((char*)&serveraddr,sizeof(serveraddr));

serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5015); server=gethostbyname("127.0.0.1"); bcopy((char*)server->h_addr,(char*)&serveraddr.sin_addr.s_addr,sizeof(server->h_addr));

printf("\nTrying to connect to the server.\n"); connect(clientsocket,(sockaddr*)&serveraddr,sizeof(serveraddr)); printf("\nConnected to the server.\n");

write(clientsocket,FILENAME,sizeof(FILENAME)); printf("\nSending filename.\n");

read(clientsocket,file,sizeof(file));

printf("\nThe file is:\n%s",file); ptr=fopen(FILENAME,"w"); fprintf(ptr,"%s",file); fclose(ptr); close(clientsocket);}



Output



SIMPLE MAIL TRANSFER PROTOCOL

Theory

SMTP is a relatively simple, text-based protocol, where one or more recipients of a

message are specified (and in most cases verified to exist) and then the message text is

transferred. It is a client-server protocol, where the client transmits an email message to the

server. Either an end-user's email client, a.k.a. MUA (Mail User Agent), or a relaying server's

MTA (Mail Transfer Agents) can act as an SMTP client.

An email client knows the outgoing mail SMTP server from its configuration. A

relaying server typically determines which SMTP server to connect to by looking up the MX

(Mail eXchange) DNS record for each recipient's domain name (the part of the email address

to the right of the at (@) sign). Conformant MTAs (not all) fall back to a simple A record in

the case of no MX. Some current mail transfer agents will also use SRV records, a more

general form of MX, though these are not widely adopted. (Relaying servers can also be

configured to use a smart host.)

The SMTP client initiates a TCP connection to server's port 25 (unless overridden by

configuration). It is quite easy to test an SMTP server using the telnet program (see below).

SMTP is a "push" protocol that does not allow one to "pull" messages from a remote

server on demand. To do this a mail client must use POP3 or IMAP. Another SMTP server

can trigger a delivery in SMTP using ETRN


http://en.wikipedia.org/wiki/ETRN

http://en.wikipedia.org/wiki/Internet_Message_Access_Protocol

http://en.wikipedia.org/wiki/Post_Office_Protocol

http://en.wikipedia.org/wiki/E-mail_client

http://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol#Sample_communications

http://en.wikipedia.org/wiki/Telnet

http://en.wikipedia.org/wiki/TCP_and_UDP_port

http://en.wikipedia.org/wiki/Transmission_Control_Protocol

http://en.wikipedia.org/wiki/Smart_host

http://en.wikipedia.org/wiki/MX_record

http://en.wikipedia.org/wiki/SRV_record

http://en.wikipedia.org/wiki/A_record

http://en.wikipedia.org/wiki/Email_address

http://en.wikipedia.org/wiki/Domain_name

http://en.wikipedia.org/wiki/Domain_Name_System

http://en.wikipedia.org/wiki/MX_record

http://en.wikipedia.org/wiki/Mail_Transfer_Agent

http://en.wikipedia.org/wiki/Email_client

http://en.wikipedia.org/wiki/Server_(computing)

http://en.wikipedia.org/wiki/Client_(computing)

http://en.wikipedia.org/wiki/Client-server

http://en.wikipedia.org/wiki/Text-based_(computing)


Server

Algorithm

* The different steps involved in the process are..........

1. Start the process.

2. Establish an UDP connection and wait for request.

3. Accept SMTP REQUEST from the client and send replyas 220:SERVICE READY.

4. Accept HELO REQUEST for which send reply as 250:REQUEST COMMAND

COMPLETED.

5. Accept MAIL TO: command for which send reply as 250:REQUEST COMMAND

COMPLETED.

6. Accept RCPT TO: command for which send reply as 250:REQUEST COMMAND

COMPLETED.

7 .Accept DATA: command for which send reply as 354:START MAIL INPUT.

8. Accept the mail contents,search for the correspondin recipient server and transmit mail to

it.

9 .If transmission is successful send reply as 250:REQUEST COMMAND COMPLETED.

10. Accept QUIT: command from the client for which send reply 221:SERVICE CLOSING.


12. Stop.

Program

/* Program to demonstrate the working of smtp protocol..............

* This program module acts as SMTP server which accepts the mail from the client and then

sends(acts as sending) it to the corresponding recipient server.

* This module establishes a UDP connection with the client and uses it for sending the

corresponding commands.

* NOTE: This module just immitate as a SMTP server.



* Compile this module as usual and execute it using the command './a.out'

//inculsion#include<iostream>#include<stdio.h>#include<string.h>


#define cls() printf("\033[H\033[J");

int main(){ int serversocket; sockaddr_in serveraddr,clientaddr; socklen_t len; char request[50]; char from[50]; char to[50]; char mail[100];


bzero((char*)&serveraddr,sizeof(serveraddr));

serveraddr.sin_family=AF_INET; serveraddr.sin_port=htons(5015); serveraddr.sin_addr.s_addr=INADDR_ANY;


bzero((char*)&clientaddr,sizeof(clientaddr)); len=sizeof(clientaddr); cls();

//waiting for the request. printf("\nWaiting for the request from the client.\n"); recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); printf("The request received is:\t%s",request);

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin);



printf("\nSending the 220:SERVICE READY COMMAND.\n"); strcpy(request,"220:SERVICE READY."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,len);

//waiting for the first command

printf("Waiting for the next request."); recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); cls(); printf("\nThe client has send:\t%s\n",request);

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin); printf("\nSending the POSITIVE COMPLETION REPLY:250 REQUEST COMMAND COMPLETED.\n"); strcpy(request,"250:REQUEST COMMAND COMPLETED."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//waiting for second command. printf("\nWaiting for the next request.\n"); recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); cls(); printf("\nThe client has send:\t%s\n",request); strcpy(from,request);

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin); printf("\nSending the POSITIVE COMPLETION REPLY:250\n"); strcpy(request,"250:REQUEST COMMAND COMPLETED."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//waiting for the third command. printf("\nWaiting for the next request.\n"); recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); cls(); printf("\nThe client has send:\t%s\n",request); strcpy(to,request);

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin); printf("\nSending the POSITIVE COMPLETION REPLY:250\n"); strcpy(request,"250:REQUEST COMMAND COMPLETED."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//waiting for the fourth command. printf("\nWaiting for the next request.\n");



recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); cls(); printf("\nThe client has send:\t%s\n",request);

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin); printf("\nSending the 354:START MAIL INPUT.\n"); strcpy(request,"354:START MAIL INPUT."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//waiting for the fifth command. printf("\nWaiting for the mail\n"); recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); strcpy(mail,request);

cls(); printf("\n\n\n\t\t\tTHE DETAILS INCLUDE:\n"); printf("\n\n\t\t%s",from); printf("\n\n\t\t%s",to); printf("\n\n\t\tMAIL:%s",mail); printf("\n\n\nSEARCHING FOR THE RECIPIENT AND MESSAGE PASSED FOR SENDING.");

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin); printf("\nSending the POSITIVE COMPLETION REPLY:250\n"); strcpy(request,"250 REQUEST COMMAND COMPLETED."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//waiting for the quit command. printf("\nWaiting for the next request.\n"); recvfrom(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,&len); cls(); printf("\nThe client has send:\t%s\n",request);

printf("\nPRESS ENTER TO SEND THE RESPONSE.\n"); fgets(request,2,stdin); printf("\nSending the 221:SERVICE CLOSING.\n"); strcpy(request,"221:SERVICE CLOSING."); sendto(serversocket,request,sizeof(request),0,(sockaddr*)&clientaddr,sizeof(clientaddr));

//closing cls(); printf("\n\n\nSERVER SHUTTING DOWN.\n"); close(serversocket);}



Output



+



Client

Algorithm

* The different steps involved in the process are...................

1.Start the process.

2.Read the required mail contents from the user.

3.Establish an UDP connection with the server.

4.Send SMTP REQUEST to the server and wait for positive reply.

5.Send the HELO command and wait for positive reply.

6.Send the MAIL FROM: command and wait for positive reply.

7.Send the RCPT TO: command and wait for positive reply.

8.Send the DATA: command and wait for positive reply.

9.Send the mail and wait for positive reply.

10.Send QUIT: command and wait for closing reply.

11.Close the connection.

12.Stop.

Program

/* Program to demonstrate the working of smtp protocol................

* This program module act as a SMTP client which works in co_ordination with an SMTP

server.

* This program establishes an UDP connection with the server and performs the required

functions.

* This module reads the mail contents from the user and sends it to a smtp server for

transmission.

* This module is compiled as 'c++ smtpclient.cpp -o b' and execute using './b' command.



//inculsion#include<iostream>#include<stdio.h>#include<string.h>



int main(){ int clientsocket; sockaddr_in serveraddr; socklen_t len; hostent *server; char from[50]; char to[50]; char mail[100]; char request[50];



len=sizeof(serveraddr); printf("\nEnter the FROM address:\n"); fgets(from,sizeof(from),stdin);

printf("\nEnter the TO address:\n"); fgets(to,sizeof(to),stdin);

printf("\nEnter the MAIL:\n"); fgets(mail,sizeof(mail),stdin);

cls();



//smtp request printf("\nPRESS ENTER TO BEGIN THE FIRST PROCESS.\n"); fgets(request,2,stdin);

printf("\nSending SMTP REQUEST to the server.\n"); strcpy(request,"SMTP REQUEST."); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

printf("\nWaiting for the server response.\n"); recvfrom(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,&len); cls(); printf("\nThe server has send:\t%s\n",request);

//sending helo request printf("\nPRESS ENTER TO SEND THE FIRST COMMAND.\n"); fgets(request,2,stdin);

printf("\nSending the HELO command\n"); strcpy(request,"HELO"); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));


//sending mail from command. printf("\nPRESS ENTER TO BEGIN THE SECOND COMMAND.\n"); fgets(request,2,stdin);

printf("\nSending the MAIL FROM request.\n"); strcpy(request,"MAIL FROM:"); strcat(request,from); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));


//sending rcpt command. printf("\nPRESS ENTER TO BEGIN THE THIRD COMMAND.\n"); fgets(request,2,stdin);

printf("\nSending the RCPT TO request.\n");



strcpy(request,"RCPT TO:"); strcat(request,to); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));


//sending data command. printf("\nPRESS ENTER TO BEGIN THE FOURTH COMMAND.\n"); fgets(request,2,stdin);

printf("\nSending the DATA request.\n"); strcpy(request,"DATA:"); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));


//sending mail. printf("\nPRESS ENTER TO BEGIN SENDING THE MAIL.\n"); fgets(request,2,stdin);

printf("\nSending the mail.\n"); strcpy(request,mail); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));


//sending the quit command. printf("\nPRESS ENTER TO BEGIN THE LAST COMMAND.\n"); fgets(request,2,stdin);

printf("\nSending the QUIT request.\n"); strcpy(request,"QUIT:"); sendto(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,sizeof(serveraddr));

printf("\nWaiting for the server response.\n"); recvfrom(clientsocket,request,sizeof(request),0,(sockaddr*)&serveraddr,&len);



cls(); printf("\nThe server has send:\t%s\n",request);

printf("\n\nCLIENT CLOSING DOWN.\n\n");


Output





REMOTE PROCEDURE CALL

Theory

When a process on machine 1 calls a procedure on machine 2, the calling process on

1 is suspended and execution of called procedure takes place on 2.Information can be

transported from the caller to callee in the parmeters and can come back in the procedure

result.No message passing is visible to the programmer. This technique is known as

RPC(Remote Procedure Call) and has become the basis for many networking applications.

Traditionally, the calling procedure is known as the client and the called procedure is known

as the server, and we will use those names here too.

The idea behind RPC is to make a remote procedure call lok as much as possible like

local one. In the simplest form, to call a remoter procedure, the client program must be bound

with a small library procedure, called the client stub, that represents the server procedure in

the server stub. These procedures hide the fact that the procedure call from the client to sever

is not local.

Program



/********************** finger.x **************************/

struct finger_out{

char message[1024];

};

program FINGER{

version FINGER_VERSION{

finger_out MyFinger() = 1;

} = 1;

} = 0x21230000;

/********************** client.c **************************/

#include <rpc/rpc.h>

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include "finger.h"

void err_quit(char *msg)

{

printf("%s\n", msg);

exit(1);

}

int main(int argc, char* argv[])

{

CLIENT *c1;

finger_out *outp;



if(argc!=2)

err_quit("usage: client <hostname>");

c1 = clnt_create(argv[1], FINGER, FINGER_VERSION, "tcp");

if( (outp=myfinger_1(NULL, c1))==NULL )

err_quit(clnt_sperror(c1, argv[1]));

printf("result: %s\n", outp->message);

exit(0);

}

/********************** server.c **************************/

#include <rpc/rpc.h>

#include <stdio.h>

#include <stdlib.h>

#include "finger.h"

finger_out* myfinger_1_svc(void *dummy, struct svc_req *rqstp)

{

static finger_out fo;

char buffer[1024];

system("finger > result.txt");

FILE *fp = fopen("result.txt", "r");

int i=0;

while( !feof(fp) ){

buffer[i++] = fgetc(fp);

}

buffer[i] = '\0';

strcpy(fo.message, buffer);

system("rm -f result.txt");

return &fo;



}

Output

compiling RPC:

there are 3 files initially, which we code... finger.x, client.c, server.c

compile in the following order...

do this in both the client and server systems

rpcgen -C finger.x (thats a C, not c)

gcc -c client.c -o client

gcc -c server.c -o server

gcc -c finger_clnt.c -o f_c

gcc -c finger_svc.c -o f_s

gcc -c finger_xdr.c -o f_x

In the server system, do:

gcc -o fs server f_s f_x

In the client system, do:

gcc -o fc client f_c f_x

Now run as before,

./fs <port>

./fc <IP> <port>



COMMON GATEWAY INTERFACE

Theory

The traditional way to handle forms and other interactive Web pages is a system

called the CGI(Common Gateway Interface).It is a standardized interface to allow web

servers to talk to backend programs and scripts that can accept input and generate html pages

in response. Usually these backends are scripts written in the Perl scripting language because

perl scripts are easier and faster to write than programs.By convention they live in a directory

called cgi-bin, which is invisible in the URL.Sometimes another scripting language, Python

is used instead of Perl.

As an example of how CGI often works, consider the case of a product from the

Truly Great Products Company that comes without a warranty registration card. Instead the

customer is told to go to www.tgpc.com to register online.On that page there is e hyperlink

that says :

Click here to register your product

This link points to a Perl script, say,www.tgpc.com/cgi-bin/reg.perl.


http://www.tgpc.com/


When this script is invoked with no parameters, it sends back an html page containing

the registration form.When the user fills in the form and clicks on submit, a message is sent a

back to this script contai8ning the values filled by the user.The perl script than parses the

parameters, makes an entry in the database for the new customer, and sends back an html

page providing a registration number and the telephone number for the help desk.

SAMPLE QUESTIONS

1. Implementation of dinning philosophers problem by multiprogramming using threads

2. Implementation of dinning philosophers problem using Semaphores

3. Implementation of dinning philosophers problem using Shared memory

4. Program to generate disk usage status report for a give UNIX/DOS formatted floppy

disk giving details like free space availability ets

5. Implementation of bankers algorithm

6. Implementation of interprocess communication using mailboxes

7. Implementation of interprocess communication using pipes

8. Implementation of PC to PC file transfer using serial port

9. Implementation of PC to PC file transfer using modem

10. S/W simulation of MAC protocols

Go Back N

Selective repeat

Sliding windows

11. Implementation of subset of SMTP using UDP



12. Implementation of subset of FTP using TCP/IP

13. Implementation of finger utility using RPC

14. Generation and processing of HTML using CGI


Os Lab Manual

Documents

linux kernel

linux applications

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startto use vi

networkos lab manual

study of red hat linux

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